E) Health risks to seafarers

E.8 Dangerous Aquatic Organisms

Details

JAROSLAW KRZYŻAK AND KRZYSZTOF KORZENIEWSKI

Edited by Jon Magnus Haga

Introduction  (by editor)

Individuals in or on water run the risk of exposure to the marine life. Particular risks to health results from exposure to predators, venomous or stinging fish and sea snakes.

Read more about dangerous aquatic organisms in Marine creatures dangerous for divers in tropical waters by Jarosław Krzyżak and Krzysztof Korzeniewski published in the International Maritime Health. Excerpts of the article is included in this chapter with the consent of the authors and the journal.

Excerpts from Marine creatures dangerous for divers in tropical waters

Predator sharks (selachimorpha)

Researchers have identified approximately 350 shark species, of which only about 20 are considered to be dangerous to humans. The smallest shark (Sqaliolus laticaudus) is only 15 cm long, while the biggest one — the whale shark — can reach the length of up to 20 m and the weight of 12 tons.

Sharks can be found in all seas and oceans around the world but are generally most prevalent in tropical waters. Many shark species are able to reach estuaries and are often spotted in shallow coastal waters. Sharks were found to have the largest brains of all fish. Apart from the senses of sight, smell, hearing, taste and touch they also have two other species-specific senses. These are the sense of electrical currents and the sense of pressure changes, the first one is mediated by special electroreceptors and the other by the lateral line. In dark waters, sharks can see 10 times better than humans.

Sharks are widely believed to be one of the most dangerous animal species in the world, which is partly the effect of the film series “Jaws” by Stephen Spielberg. In fact, only 27 of all the living shark species have been known to attack people or boats, of which no more than 10 species are considered dangerous to humans. The risk of a shark attack is much higher in shallow waters — the animals most often attack swimmers, surfers, snorkelers and spearfishers. At deep depths (> 20 m) the risk is much lower. A total of 150–200 shark attacks on humans are recorded each year, but less than 6% of the attacks are fatal. An analysis of the shark attack rate from 1960–2015 for 14 countries demonstrated the rate of merely one shark attack per one million people, but found that around 10% of the attacks involved scuba divers.

Sharks have a poor sense of sight and are more attracted to the smell of blood or vibrations than the mere presence of a human in the water. In fact, their excellent sense of smell compensates for their poor eyesight and enables them to sense their victims from long distances. Sharks are able to detect electrical signals produced by the living creatures. If they are injured or scared they tend to be aggressive. Shark attacks can be either provoked by the behaviour of a scuba diver, when a shark tries to defend itself, or unprovoked, when a shark attack is unexpected and occurs for no clear reason. In general, a shark attack is more likely to occur under the following conditions: when the water temperature is > 20°C, when there is blood in the water and in areas where the number of prey is limited.

In order to minimize the risk of getting attacked by a shark, swimmers and divers are recommended to follow a few simple rules. You should avoid swimming or diving at night or dusk as it is the time when sharks are most active and usually go hunting. You must not get into the water if you have an open bleeding wound (this also applies to menstruating women). Avoid waters which are fished and where fishing nets are emptied. If you see a shark approaching you, remain calm and be careful. Try not to make quick movements or to escape as it might provoke an attack. You should rather try to withdraw calmly without losing the sight of the shark. Never try to feed sharks as it may also provoke an attack. Be careful not to come into contact with the rough skin of a shark, it may cause an injury, and the bleeding may in turn provoke an attack. In order to minimize the risk of a potential attack stay calm and try not to move, perhaps the shark will swim away.

If you are attacked, you should hit the shark hard in the nose, eyes or the gills — this may scare it away. Another effective method of scaring the shark off is to direct a stream of air bubbles from the regulator towards the shark or to swim directly towards the approaching animal — this usually makes the shark turn away making it possible to avoid a direct contact with the shark. Shark bite injuries are usually quite severe and result in massive tissue loss — a shark tears off pieces of flesh from the victim with its sharp teeth. Massive bleeding that follows a shark attack can attract other predators. In case of a shark attack, the victim should be removed from the water as quickly as possible. The bleeding must be controlled, the wound dressed, and the victim should be taken to hospital immediately. A vast majority of shark attacks casualties die of a haemorrhagic shock.

Barracudas (sphyraenidae)

There are about 20 known species of the barracuda. All of the barracuda species are predators but some are so small that they are not dangerous to humans. Interestingly, people living in the West Indies fear barracudas even more than they fear sharks and in some parts of the world it is the barracuda, and not the shark, which is called the ‘the king of the coral reef’. The fish is considered to be one the most dangerous marine predators. Barracudas resemble large eels. Their average length is 1–1.5 m, but some species can grow up to 2.5 m.

Barracudas have long sharp teeth with which they can inflict major injuries and in some cases even bite off a person’s fingers or the whole hand. Barracuda normally reside near the coral reefs and in rock crevices. They usually attack to defend their territory rather than satisfy their hunger. They are known to form schools, which are dangerous to other marine animals. They show no fear of humans and are often seen to stay close to scuba divers. Unprovoked barracuda attacks are rare.

An interesting fact is that the fish is attracted by bright colours and glittering objects such as scuba gear. For this reason, a barracuda may, for example, mistake a glittering watch for pray and attack a diver causing severe injuries. Barracuda bites take a long time to heal and usually require in-patient treatment.

Moray eels (muraenidae)

There are approximately 20 genera of the moray eel. Some may reach the length of up to 3 m, the width of over 30 cm, and the weight of up to 30 kg. They have a long, eel-shaped, slightly flattened body and very wide and strong jaws. They can be found in the coral reefs where they normally reside under the rocks or in crevices.

Moray eels rarely attack humans. The attacks are usually provoked by people, e.g., if a diver comes too close and puts their hand inside a crevice where a moray eel is hiding, the fish is very likely to attack in order to defend its territory.

You should not feed, touch or approach moray eels as this can scare the fish and provoke an attack. Moray eels often look out for their prey in shallow waters and therefore it is possible to come across the fish while wading in the sea close to the rocks or the reefs.

Triggerfish (balistidae)

Scientists have identified more than 25 different species of the triggerfish. The fish can be found in all tropical waters. It is considered to be the most aggressive fish inhabiting the coral reef. Triggerfish is a solitary species. It has large and sharp teeth adapted for crushing corals and therefore its bite can cause a severe injury. The green giant triggerfish is the largest species of the triggerfish genus, and can reach the length of up to 90 cm. The animals show no fear of scuba divers and can attack them if they approach their nest. The triggerfish is found at the depth of up to 50 m.

The serranid fish (serranidae)

This extremely large fish can be found in the tropical waters of the Indo-Pacific Ocean and the Caribbean Sea. There are approximately 400 different species of the serranid fish belonging to 67 genera. Some species are small, while others can be very large, e.g., the giant grouper. Epinephelinae are the largest of the Serranidae family, their average length is 1.5–2.5 m, but some can grow up to 3.5 m and weigh as much as 300 kg. The serranid fish should be treated as potentially dangerous to humans because of its large size, wide jaws and sharp teeth. They show no fear of scuba divers. They must not be fed as they can bite a diver on the hand.

The surgeonfishes (acanthuidae)

These brightly coloured fishes are commonly found in tropical waters of the coral reefs. The size of the different species of the surgeonfish ranges from 15 cm to more than 1 m, but their average length is around 50 cm. There are around 80 species belonging to the surgeonfish family. They form schools and can be found at the depth of up to 100 m.

The surgeonfish is a territorial species which tends to be aggressive towards other fish of their own species. Although they are not predatory, they may potentially be dangerous to scuba divers because of their extremely sharp spines on each side of their tail that can cause a severe injury to anyone who tries to touch or hold the fish in a careless manner. If it is scared and cannot retreat, the fish can attack a human using its scalpel-like spines. The fish can inflict deep lacerated wounds by moving its tail.

Venomous fish

A vast majority of venomous fish produce and use their toxins for self-defense. The venomous spines or barbs, at the base of which venom glands are located, can reach the length of up to 30 cm in some species. The greater weever, for example, which can be found along the coastline of the Mediterranean Sea and the east coasts of the Atlantic Ocean have their venomous spines located on each of their gill covers and their dorsal fin. The fish can inflict extremely painful puncture wounds. Most species of the venomous fish are known to lead a sedentary lifestyle and are usually found in shallow coastline waters. When a person is wading in the shallow waters, they may accidentally step on a venomous marine creature and sustain a puncture wound on the sole of their foot. For this reason, it is not safe to walk barefoot on the beach or in the waters rich in marine life. Instead, swimmers are recommended to wear specially designed water shoes to prevent possible injuries.

Rays (batoidea)

Rays belong to one of the largest groups of marine animals. There are seven recognized families of Batoidea, of which two possess venomous spines — these are Dasyatidae, commonly known as stingrays, and Myliobatidae including eagle and manta rays. Rays inhabit calm and shallow waters such as lagoons and can be found on the sandy seabed of the coral reefs.

The most common rays include: the common stingray (Dasyatis pastinaca), which lives in the Mediterranean Sea and the Black Sea, the southern stingray (Hypanus americanus) inhabiting the Gulf of Mexico and the Caribbean Sea, and the spotted eagle ray (Aetobatus narinari) which can be found across all tropical seas and oceans.

Stingrays spend most of their time partly buried in the sand on the ocean floor, with only their eyes and a part of their tail sticking out. Stingrays will usually only attack to defend themselves when they are disturbed or accidentally stepped on. They attack by whipping their tail which is equipped with a venom spine at its end. The stingrays usually sting people in their feet and the lower extremities less commonly on other parts of the body. The pain starts immediately or within 10 min of the sting. It is sharp, excruciating or throbbing. The wound itself is either a laceration or a puncture wound. The removal of the stingray spine causes further tissue damage. The sting site becomes swollen and the surrounding skin turns white, then blue and eventually red. A person stung by a stingray may experience signs and symptoms which are indicative of poisoning, such as blood-tinged sputum, vomiting, diarrhoea, sweating, tachycardia, muscle paralysis. A sting by a stingray may be fatal.

The scorpionfishes (scorpaenidae)

The family of the Scorpaenidae is large and includes around 100 species which inhabit both tropical and temperate seas and oceans. The Scorpaenidae includes one of the world’s most venomous fishes, which can normally be found close to coral reefs. The largest of the species grow up to 1 m long. Most of the fish have camouflage coloration.

Because of the differences in the structure of their venom glands they are divided into the lionfish (Pterois) and the scorpionfish (Scorpaena). They can be found in shallow waters, close to the coral reefs, the ocean bed and sandy beaches. They show no fear of people. Their venomous spines are hidden beneath their elongated fins.

Because of their camouflage coloration the scorpionfish are difficult to spot, especially in shallow waters, where they normally reside. When disturbed they take a defensive position and prepare for an attack by erecting their dorsal spines and spreading their other fins. Both the lionfish and the scorpionfish have up to 20 sharp spines with venom glands located at their bases. The lionfish spines are long and straight while the scorpionfish have shorter and thicker spines.

When a person gets stung by either of the two species, they will immediately feel acute throbbing pain which radiates from the sting site all through the affected limb and lasts for up to several hours. The injured site turns white and then blue and an inflammatory response occurs. The symptoms which are associated with a sting by a scorpionfish or a lionfish include vomiting, diarrhoea, arthralgia, delirium, convulsions, shortness of breath, arrhythmia, hypotonia and in extreme cases cardiac arrest.

The stonefishes (synanceiidae)

The fish belonging to the Synanceiidae family, commonly known as the stonefish, lives in shallow waters of the coral reefs. They can be found inside cracks, caves and crevices or buried in the sand on the ocean floor. They are considered to be one of the most venomous and therefore dangerous marine animals. They grow up to 40 cm long, on average. They are found in the Red Sea, the Indian Ocean and the Pacific as well as in the coastal regions of Australia. They have 13 short but thick dorsal fin spines at the base of which their multiple venom glands are located.

People usually get stung as they accidentally step on the fish which is lying motionless on the ocean floor often partially buried in the sand. The injuries caused by the stonefish are much more serious than those inflicted by the scorpionfish. The pain can last for many days and it can be so excruciating that it may result in a loss of consciousness. A swelling and an inflammatory response usually occurs at the sting site; in some cases muscular paralysis may ensue. Other signs and symptoms of a sting by a stonefish include: lymphadenopathy, arthralgia, vomiting, delirium, convulsions, shortness of breath, arrhythmia and eventually death in some cases.

If stung by a stonefish, a victim must immediately leave the water and seek medical attention as quickly as possible. The treatment is long and can take several months, but even if it is successful, the poisoning can cause permanent health damage.

The weevers (trachinidae)

The fish belonging to the Trachinidae family are one of the most venomous marine creatures inhabiting the temperate seas and oceans. The species is distributed in warm waters along the east coast of the Atlantic Ocean, i.e., along the coasts of Norway, the British Isles as well as along the coasts of the Mediterranean Sea and the Black Sea.

The fish inhabits the muddy ocean floor where it often buries itself in the sand. It can be found both in deep and shallow waters (at the depth of only 1 m) and therefore it might be dangerous for swimmers or those wading in the water along the coast as well as for scuba divers.

Its venom apparatus consists of a venomous spine above the eye, long spines on each of their gill covers, 5–7 dorsal fin spines and 2 anal fin spines all connected with venom glands located at their bases. Its venom shows both neurotoxic and chemotoxic properties.

The sting causes excruciating pain which radiates all through the affected limb; the pain is most intense after 30 min of the sting. Sometimes the pain is so severe that a victim of a sting can lose consciousness. Redness and swelling occur around the sting site, which persist for around 10 days.

An infection of the affected site may lead to tissue necrosis. The common signs and symptoms of a weever sting include: excitement, tremors, sweating, vomiting, arthralgia and in more severe cases: shortness of breath and cyanosis, arrhythmia, delirium, disturbance of consciousness and convulsions. A sting by the weever fish can cause death in extreme cases. The treatment and the convalescence are long and can take up to several months.

The stargazers (uranoscopidae)

The stargazer is a relatively small fish, reaching the length of 40 cm. The species inhabit the east coastline of the Atlantic Ocean (from Portugal to the Republic of South Africa), the Mediterranean Sea and the Black Sea. The fish resides on the ocean floor and spends its time buried in the sand.

The stargazers are active during daytime. Some species have a worm-shaped lure, which they use to attract their prey’s attention. The venomous apparatus of a stargazer consists of two large venom spines located on their gill covers above their pectoral fins.

A sting by the stargazer causes a painful injury and swelling of the affected site. In some cases the pain is so intense that it may lead to a loss of consciousness. The common signs and symptoms associated with the stargazer sting include: shivers, sweating, dizziness, arthralgia, shortness of breath, arrhythmia, convulsions and loss of consciousness. A sting inflicted by the Atlantic stargazer (Uranoscopus scaber) can cause death.

The rabbitfishes (signidae)

The rabbitfish, also known as the spinefoot, are a small species (their average length is 35 cm) commonly found in the Red Sea, the Indo-Pacific and Polynesia. They resemble the surgeonfish.

The venomous apparatus of the rabbitfish consists of 24 spines connected with venom glands located at their bases. The signs and symptoms which occur after getting stung by the rabbitfish are similar to those associated with a sting by the scorpionfish and usually include: acute excruciating pain, cyanosis, arthralgia, shortness of breath, arrhythmia and convulsions. Although quite serious, the signs and symptoms are not life-threatening.

Other species of venomous fish which are distributed in warm waters include: catfish, gafftopsail catfish, chimarea, toadfish, dragonets (e.g., spotted dragonet), snake eels (e.g., Ophichths semicinctus). The wounds inflicted by these species are usually quite painful and cause local signs and symptoms including redness, swelling, infection at the sting site, occasionally tissue necrosis and hard-to-heal wounds.

The electrical rays (torpedinidae)

Torpedinidae is a family of electric rays. They are not particularly dangerous to scuba divers, however, a close encounter with the fish can be very unpleasant. The fish is equipped with electric organs and is capable of generating electricity which they either use for self-defence or to capture their prey. They are primarily found along the coastline of the Mediterranean Sea, the Indian Ocean, the Pacific and the Atlantic Ocean as well.

The best known species of the electric rays include: the leopard torpedo (Torpedo panther), the common torpedo (Torpedo maculata), the Atlantic torpedo (Torpedo nobiliana) and the Brazilian electric ray (Narcine brasiliensis).

Electric rays have flat, disc-shaped body. They are usually brightly coloured with darker spots on the top of their body; they have small retracted eyes, two dorsal fins and a well-developed caudal fin. They have two electric organs which are placed on both sides of their head. The largest species are capable of generating an electric shock of up to 300 volt.

The electric rays differ in size; the smallest species are no more than 20 cm long, while the largest ones can grow up to the length of 180 cm and can weigh a few dozen kilograms. They are solitary bottom dwellers which spend most of their time buried in the sand or mud.

Approaching or touching the animal may provoke an electric discharge, which can be very unpleasant and may even immobilize a diver for a short period. The recovery is swift and the electric shock from the ray causes no long-term complications.

Cnidarians

Cnidarians encompass a broad category of marine species which belong to the group of Coelenterata and include jellyfishes (Scyphozoa), sea anemones (Actiniaria) and corals (Anthozoa).

Jellyfish (scyphozoa)

Jellyfish (scyphozoa) are potentially dangerous to swimmers and scuba divers because of their venomous properties. Their venom apparatus consists of numerous nematocysts which are small elongated venom-filled capsules. When attacking their prey or trying to defend themselves they discharge thread-like spines from the nematocysts and inject the venom into the body of their prey or an attacker.

Some jellyfish have tentacles of more than 15 m long. For this reason, if a diver sees anything which might potentially be a jellyfish, they should stay away. Even beached and dead jellyfish can inflict severe stings. In most cases, a sting by a jellyfish, corals or sea anemones causes an inflammatory response — with redness or a burn occurring locally.

Some jellyfish (e.g., Dactylometra, Chyropsalmus or Carybdea) are particularly venomous; their sting can cause generalized signs and symptoms as well as severe skin lesions including tissue necrosis. Such stings are hard to heal.

The Portuguese man-of-war (Physalia physalis) can be potentially dangerous to scuba divers who go diving in the Indian Ocean or the Atlantic Ocean. Although it is often mistaken for jellyfish, it is in fact a colonial hydrozoan which lives on the surface of the ocean.

The Portuguese man-of-war has purple-blue pneumatophore and extremely venomous tentacles which are up to several meters long. The stings inflicted by the tentacles are painful and extremely dangerous as they can cause a severe poisoning, and in extreme cases even lead to death of an affected person.

The sea wasps (Chironex fleckeri) are known to have caused around 60 deaths in the Great Barrier Reef off the coast of Australia. The sea wasp is considered to be one of the most venomous jellyfish in the world. Its bell is relatively small, only around 20 cm in diameter, but the creature has several dozen long transparent tentacles. Its venom is so potent that it can kill a person within minutes.

Another dangerous jellyfish that can be found in tropical waters along the coasts of Australia is the Irukandji jellyfish (Carukia barnesi), a small species of the jellyfish which is the size of a human finger. Its sting can result in the Irukandji syndrome associated with catecholamine release.

A sting from cnidarian species can cause a variety of signs and symptoms, including the anaphylactic shock.

When swimming or diving in waters where cnidarians are distributed, you should always be wearing a diving suit that protects your skin from jellyfish stings. The recommended first aid for a jellyfish sting (urticaria or contact dermatitis) is to rinse the affected area with vinegar. On some tropical beaches, you will even find bottles of vinegar to be used as first aid to treat stings. Obviously, not all jellyfish stings can be treated with vinegar only. If you are stung by the Portuguese man-of-war, vinegar should not be used as it can cause nematocysts to activate and trigger a stronger inflammatory response. In severe cases, when the sting is life-threatening, the only treatment option will be to give the victim cardiopulmonary resuscitation; CPR should be performed by qualified medics. Administration of antivenom is an effective treatment option; however, it is only available for stings by a limited number of sea stingers, e.g., the sea wasp.

Sea anemones (actiniaria)

Sea anemones are either sedentary or semi-sedentary species in the class of Hexacorallia. The latter species are capable of moving slowly on their pedal disc with which they attach to hard surfaces. They live singly and are known for their vivid colors which they owe to carotenoid pigments.

Some species live in symbiosis with other animals, e.g., small fish. Sea anemones are well adapted to a wide range of habitats and can be found throughout the world across all seas and oceans and at various depths. Yet, a vast majority of the species inhabit tropical waters. Sea anemones have cylindrical body which varies in size from a few millimeters to as much as 1.5 m in diameter.

Anemones have a ring of tentacles growing around its central mouth and multiple stinging cells which they use in self-defense and to hunt prey. Sea anemones are predators, they use venom to paralyze their prey and next their tentacles to move the prey into the mouth. The tentacles are also used for catching the passing plankton.

Corals (anthozoa)

Corals are marine invertebrates which belong to the class of Cnidaria. The species have a structure of a polyp. Polyps form colonies which usually grow in shallow waters along the coast but some species can be found as deep as 6000 m. Attached to the ocean floor, they inhabit tropical or sub-tropical waters that are well-oxygenated and rich in sunlight. There are more than seven thousand different species of corals that can be classified into two broad subclasses:

Hexacorallia and Octocorallia. Singly living species vary in size from several millimeters to more than 10 cm, but the largest ones can grow up to 1.5 m in diameter. Coral polyps produce limestone which forms the structure of the ecosystem commonly known as the coral reef. Most species are sessile creatures (they lack the ability of self-locomotion) but some may be surprisingly mobile. Most corals feed on zooplankton, but larger species are capable of catching bigger prey, such as crustaceans, mollusks and small fish. They paralyze and catch the prey using stinging cells which are located on their tentacles. Many species of crustaceans, starfish and fish feed on corals [34].

Molluscs and echinoderms

Both swimmers and divers are at risk of exposure to venomous molluscs, snails and cephalopods (which are equipped with a venom-producing apparatus) and sea urchins.

Gastropods (gastropoda)

Marine species of gastropods have colorful and beautifully sculptured spiral shells which are desired by shell collectors. Many tropical snails, however, produce toxic venom, which can cause a severe poisoning or in extreme cases even death.

Cone snails and terebra snails have a harpoon-like tooth loaded with venom which they fire into the prey. Once the prey has been stung, the venom is injected into its body under high pressure. Although murex snails and Aplysia species are not equipped with a venom apparatus, they are capable of producing toxic secretions in their salivary glands to overpower their prey. Both cone and terebra snails inflict puncture wounds.

If you are stung, the sting site turns white at first and then cyanosis, itching, numbness, intense pain and a burning sensation follow. The localized symptoms may soon progress into generalized ones including muscle paralysis, difficulty breathing and arrhythmia, and in extreme cases death. Gastropod stings should be managed in the same way as stings by venomous fish.

The most venomous species of marine gastropods include the textile cone (Conus textile), the geography cone (Conus geographus) and terebra (Terebra maculata). The species are widely distributed in the Red Sea, the Indian Ocean and the Pacific Ocean. Murex haustellum, the species classified in the family of murrex snails, which is capable of producing toxic salivary secretions is primarily found in the Mediterranean Sea and the Black Sea.

Octopuses (octopoda)

All octopuses are equipped with venom apparatus that is capable of producing highly toxic secretions that enter the victim’s body through a puncture wound inflicted by the animal’s horn beak. The wound is usually quite small, but it may bleed heavily and be associated with a burning or itching sensation spreading all through the affected limb.

The octopus bite causes redness, swelling and a rise in body temperature. In severe cases signs and symptoms of a poisoning may ensue, including a headache, vomiting, difficulty breathing and arrhythmia, the last two symptoms can be potentially life-threatening. Injuries inflicted by octopuses as well as a poisoning by an octopus should be managed in the same way as stings by venomous fish.

The blue-ringed octopus, a small species with an arm span of only up to 20 cm, is considered one of the most dangerous marine animals as its toxin can be deadly to humans. When disturbed, the octopus can become aggressive and attack an intruder. It is known to attack and kill animals which are much bigger and stronger. The blue-ringed octopus is found in the Pacific Ocean, especially along the northern costs of Australia. Each year, several people are reported to die from a sting by this marine creature.

Octopus vulgaris, the giant Pacific octopus with an arm span of more than 6 m, is venomous both to marine animals as well as to humans. It mainly inhabits tropical waters but some species can also be found in the Black Sea, the Mediterranean Sea or the Caribbean Sea.

Sea urchins (echinoidea)

Sea urchins are one of the most common species of echinoderms. Sea urchins are found in both tropical and temperate climates. The long-spined urchins are considered the most dangerous because their sharp venomous spines can easily puncture the human skin and break off inside the body.

Sea urchins are venomous and their sting can cause both localized and systemic poisoning. A sting by a sea urchin is painful and the pain can radiate all through the affected limb. In extreme cases a person who has been stung by a sea urchin may experience difficulty breathing, fits or seizures, face muscles paralysis, partial paralysis of other body parts or a loss of consciousness. The severity of signs and symptoms will depend on the species of the sea urchin and the number of stings. Deaths from sea urchin stings are extremely rare.

The stings are managed in the same way as stings by other venomous fish. The removal of broken spines may be difficult and may require a surgical procedure. The black long spine urchin (Diadema setosum) is a typical long-spined sea urchin with the body of 10 cm in diameter and extremely long and sharp spines that can reach the length of more than 30 cm. The species can be found throughout the Indo-Pacific and in the Red Sea.

Sea snakes

Marine snakes belong to the Elapidae family and include approximately 50 different species. Although they are marine animals, some can be found near estuaries. Sea snakes are primarily found in tropical waters of the Indo-Pacific Ocean. They are adapted to a variety of habitats. The yellow-bellied sea snake, for example, is known to be drifting deep sea, moving extremely long distances with the ocean currents but some species are found in shallow coastline waters.

Marine snakes are one of the most venomous animals in the world. Some sea snakes have venom which is several times more potent than that of the Indian cobra. The mortality from a sea snake bite has been estimated at 15–30%. Fortunately, a majority of marine snakes have an underdeveloped venom apparatus and are generally not aggressive towards people, and tend to stay away from swimmers and scuba divers. Still, a direct contact with the animals should be avoided as their bite may be life-threatening. Most species are colourful and do not exceed the length of 1 m, but the largest sea snakes can grow up to around 2 m. Marine snakes are most dangerous to fishermen. A bite can occur when fishers are emptying the fishing nets or while they are wading in shallow waters. The signs and symptoms of sea snake envenomation develop quite slowly. In some cases, no signs or symptoms will occur, and a person may not even know that they had been bitten.

However, after a bite by a more venomous snake, signs and symptoms usually begin within 30 to 90 min. Sea snake venom contains a neurotoxin affecting the nervous system. The initial symptoms of envenomation might include excitement and agitation in some cases or anxiety and restlessness in other. The victim can feel mild pain at the bite site. Haemolysis, rhabdomyolysis and a respiratory failure will often ensue. Tongue stiffness, muscle numbness weakness and pain can also occur. Muscle paresis and paralysis gradually spread upwards from the lower extremities towards the torso and then the head. This results in trismus, facial and eye muscles paralysis. Eventually complete muscle paralysis and kidney damage occur followed by bradycardia, difficulty breathing, cyanosis, convulsions, vomiting, loss of consciousness and eventually death which is due to the paralysis of the respiratory muscles. In most cases, a bite by a sea snake will leave no visible marks on the skin of the victim but it will cause certain systemic signs and symptoms resulting from the neurotoxic effects of venom. A bite by a sea snake is a medical emergency, the victim will need to get prompt medical assistance and will generally require in-hospital treatment (dialysis, mechanical ventilation, maintaining fluid and electrolyte balance).

The beaked sea snake, the yellow-lipped sea krait and the annulated sea snake also known as the blue-banded sea snake (Hydrophis cyanocinctus) are typical representatives of marine snakes.

The baked sea snake (enhydrina schistose)

This highly venomous sea snake is considered to be the most dangerous of all marine snake species. The species is known to be aggressive and is responsible for the majority of deaths from sea snakes bites in humans. It grows up to the length of around 2 m and is found all throughout the Indian Ocean including in the Persian Gulf, the warm waters of the Malay Archipelago, the northern coasts of Australia and the coasts of New Guinea.

The annulated sea snake (hydrophis cyanocintus)

Although it is generally less dangerous than the beaked sea snake, its bite may also be potentially life-threatening to scuba divers. Its maximum length is approximately 130 cm; the largest animals can grow up to 150 cm. It is often found in shallow coastline waters overgrown with mangrows. During the wet season the species travel inland — sometimes they can be spotted a few kilometers away from the shore. It is commonly distributed in the Indian Ocean, from the Persian Gulf to Japan and Australia.

The blue-ringed sea krait (liticauda laticaudata)

The colorful blue-ringed sea krait is one of the most common sea snake. It has a black head with characteristic yellowish patches. Its average length is around 1 m. Although the species is not aggressive towards humans and its bites are rarely reported, the snakes can be dangerous as they have very potent toxic venom. The species can be found in the waters of the Indian Ocean — along the coasts of India, the Malay Archipelago, northern coasts of Australia and New Guinea, the Philippines and the Salomon Islands.

The yellow-lipped sea krait (laticauda colubrina)

The yellow-lipped sea krait, also known as the banded sea krait or the colubrine sea krait, is one of the most common species of the sea snakes inhabiting the coral reefs of the Indo-Pacific. It has characteristic black rings all throughout the length of its body and vertically flattened paddle-like tail which is adapted for swimming. The upper surface of the snake’s body has a grayish color, while the belly is yellowish. The black rings narrow or are interrupted at the bottom part of the snake’s body.

The yellow-lipped sea krait is one the few sea snakes which regularly comes ashore, especially at dusk and during the night. On average, it grows up to 140 cm long. The yellow-lipped sea krait has extremely potent toxic venom, which the snake uses to paralyze their prey. Fortunately, the snake is not aggressive towards humans. Nevertheless, you must remain extremely cautious whenever getting close to the species.

The yellow-bellied sea snake (pelamis platurus)

The yellow-bellied sea snake is yet another marine snake which can potentially be dangerous to humans. It is the only pelagic sea snake and as such it spends its entire life away from the shallow waters of the coastline. It can be found in tropical waters across the Indian Ocean and the Pacific.

The snake is bicolored — black on the upper surface of its body and yellow at the belly with the two colors sharply demarcating from each other. Its length rarely exceeds 1 m. Bites in humans are extremely rare, but the snake’s venom is particularly potent and highly toxic.

The olive-brown sea snake (aipysurus laevis)

The olive-brown sea snake is commonly found along the coasts of New Guinea, Indonesia, New Caledonia and the northern coasts of Australia. Their body is thick and massive, the largest adults can exceed 1.8 m long. It has a flattened, paddle-like tail with slightly frayed edges. The snake is not aggressive and will not attack until provoked, but its bite can be dangerous to humans as its venom is highly toxic.

 

REFERENCES:

  1. Krzyżak J, Korzeniewski K. Medicine for divers [in Polish]. Publishing House 4Font, Poznań 2020, pp. 674–707.
  2. Gatti CM, Chung K, Oehler E, et al. Screening for predictors of chronic ciguatera poisoning: an exploratory analysis among hospitalized cases from French Polynesia. Toxins (Basel). 2021; 13(9), doi: 10.3390/toxins13090646, indexed in Pubmed: 34564650.
  3. Neves CK, Goldani LZ. Ciguatera fish poisoning in Brazilian traveler to Caribbean. Braz J Infect Dis. 2019; 23(3): 200–202, doi: 10.1016/j.bjid.2019.06.004, indexed in Pubmed: 31301279.
  4. Caldicott D, Mahajani R, Kuhn M. The anatomy of a shark attack: a case report and review of the literature. Injury. 2001; 32(6): 445–453, doi: 10.1016/s0020-1383(01)00041-9.
  5. Ganske W, Sharma R, Kaminski S, et al. Shark-Related injuries in the United States: a national trauma data bank analysis. Am Surg. 2021 [Epub ahead of print]: 31348211024171, doi: 10.1177/00031348211024171, indexed in Pubmed: 34126790.
  6. Sprivulis P. Western Australia coastal shark bites: a risk assessment. Australas Med J. 2014; 7(2): 137–142, doi: 10.4066/AMJ.2014.2008, indexed in Pubmed: 24611078.
  7. Lippmann J. Fatal shark attacks on divers in Australia, 1960-2017. Diving Hyperb Med. 2018; 48(4): 224–228, doi: 10.28920/dhm48.4.224-228, indexed in Pubmed: 30517954.
  8. Korzeniewski K. [Land and marine fauna constituting a threat for recreational divers in the tropics]. Pol Merkur Lekarski. 2008; 25(147): 294–297, indexed in Pubmed: 19112854.
  9. Ballen GA. Nomenclature of the Sphyraenidae (Teleostei: Carangaria): a synthesis of fossil- and extant-based classification systems. Zootaxa. 2019; 4686(3): zootaxa.4686.3.5, doi: 10.11646/zootaxa.4686.3.5, indexed in Pubmed: 31719480.
  10. Smith DG, Bogorodsky SV, Mal AO, et al. Review of the moray eels (Anguilliformes: Muraenidae) of the Red Sea, with description of a new species. Zootaxa. 2019; 4704(1): zootaxa.4704.1.1, doi:10.11646/zootaxa.4704.1.1, indexed in Pubmed: 32229893.
  11. Riordan C, Hussain M, McCann J. Moray eel attack in the tropics: a case report and review of the literature. Wilderness Environ Med. 2004; 15(3): 194–197, doi: 10.1580/1080-6032(2004)15[194:meaitt]2.0.co;2.
  12. Matsuura K. Taxonomy and systematics of tetraodontiform fishes: a review focusing primarily on progress in the period from 1980 to 2014. Ichthyol Res. 2014; 62(1): 72–113, doi: 10.1007/s10228-014-0444-5.
  13. Rimmer M, Glamuzina B. A review of grouper (Family Serranidae: Subfamily Epinephelinae) aquaculture from a sustainability science perspective. Rev Aquac. 2017; 11(1): 58–87, doi: 10.1111/raq.12226.
  14. Sorenson L, Santini F, Carnevale G, et al. A multi-locus timetree of surgeonfishes (Acanthuridae, Percomorpha), with revised family taxonomy. Mol Phylogenet Evol. 2013; 68(1): 150–160, doi:10.1016/j.ympev.2013.03.014, indexed in Pubmed: 23542000.
  15. Brown TP. Diagnosis and management of injuries from dangerous marine life. MedGenMed. 2005; 7(3): 5, indexed in Pubmed: 16369231.
  16. Hornbeak KB, Auerbach PS. Marine envenomation. Emerg Med Clin North Am. 2017; 35(2): 321–337, doi: 10.1016/j.emc.2016.12.004, indexed in Pubmed: 28411930.
  17. Henn A, Pérignon A, Monsel G, et al. Marine envenomations in returning French travellers seen in a tropical diseases unit, 2008–13.J Travel Med. 2016; 23(2): tav022, doi: 10.1093/jtm/tav022, indexed in Pubmed: 26858271.
  18. Todd J, Edsell M. A diver’s guide to subaquatic envenomation in the Mediterranean. Diving Hyperb Med. 2019; 49(3): 225–228, doi: 10.28920/dhm49.3.225-228, indexed in Pubmed: 31523798.
  19. Alcoba G. [Sea bathing dangers: marine envenoming, trauma, and infections]. Rev Med Suisse. 2020; 16(693): 984–988, indexed in Pubmed: 32401438.
  20. Diaz JH. Marine scorpaenidae envenomation in travelers: epidemiology, management, and prevention. J Travel Med. 2015; 22(4): 251––258, doi: 10.1111/jtm.12206, indexed in Pubmed: 25884785.
  21. Prentice O, Fernandez WG, Luyber TJ, et al. Stonefish envenomation. Am J Emerg Med. 2008; 26(8): 972.e1–972.e2, doi: 10.1016/j.ajem.2008.01.055, indexed in Pubmed: 18926380.
  22. Gorman LM, Judge SJ, Fezai M, et al. The venoms of the lesser (Echiichthys vipera) and greater (Trachinus draco) weever fish: a review. Toxicon X. 2020; 6: 100025, doi: 10.1016/j.toxcx.2020.100025, indexed in Pubmed: 32550581.
  23. Fricke R. Two new species of stargazers of the genus Uranoscopus (Teleostei: Uranoscopidae) from the western Pacific Ocean. Zootaxa. 2018; 4476(1): 157–167, doi: 10.11646/zootaxa.4476.1.15, indexed in Pubmed: 30313350.
  24. Borsa P, Lemer S, Aurelle D. Patterns of lineage diversification in rabbitfishes. Mol Phylogenet Evol. 2007; 44(1): 427–435, doi: 10.1016/j.ympev.2007.01.015, indexed in Pubmed: 17383906.
  25. Jouiaei M, Yanagihara AA, Madio B, et al. Ancient venom systems: a review on cnidaria toxins. Toxins (Basel). 2015; 7(6): 2251–2271, doi: 10.3390/toxins7062251, indexed in Pubmed: 26094698.
  26. D’Ambra I, Lauritano C. A review of toxins from cnidaria. Mar Drugs. 2020; 18(10), doi: 10.3390/md18100507, indexed in Pubmed: 33036158.
  27. Silva Cavalcante MM, Ribeiro Rodrigues ZM, Hauser-Davis RA, et al. Health-risk assessment of Portuguese man-of-war (Physalia physalis) envenomations on urban beaches in S o Luís city, in the state of Maranh o, Brazil. Rev Soc Bras Med Trop. 2020; 53: e20200216, doi: 10.1590/0037-8682-0216-2020, indexed in Pubmed: 32997052.
  28. Piontek M, Seymour JE, Wong Y, et al. The pathology of venom and known biological mechanisms. Toxicon X. 2020; 6: 100026, doi: 10.1016/j.toxcx.2020.100026, indexed in Pubmed: 32550582.
  29. Carrette TJ, Underwood AH, Seymour JE. Irukandji syndrome: a widely misunderstood and poorly researched tropical marine envenoming. Diving Hyperb Med. 2012; 42(4): 214–223, indexed in Pubmed: 23258458.
  30. Little M, Pereira P, Seymour J. Differences in cardiac effects of venoms from tentacles and the bell of live: using non-invasive pulse wave Doppler. Toxins (Basel). 2020; 13(1), doi: 10.3390/toxins13010019, indexed in Pubmed: 33383955.
  31. Pereira JC, Szpilman D, Haddad Junior V. Anaphylactic reaction/angioedema associated with jellyfish sting. Rev Soc Bras Med Trop. 2018; 51(1): 115–117, doi: 10.1590/0037-8682-0044-2017, indexed in Pubmed: 29513832.
  32. Tibballs J. Australian venomous jellyfish, envenomation syndromes, toxins and therapy. Toxicon. 2006; 48(7): 830–859, doi: 10.1016/j.toxicon.2006.07.020, indexed in Pubmed: 16928389.
  33. O’Reilly GM, Isbister GK, Lawrie PM, et al. Prospective study of jellyfish stings from tropical Australia, including the major box jellyfish Chironex fleckeri. Med J Aust. 2001; 175(11-12): 652–655, doi: 10.5694/j.1326-5377.2001.tb143765.x, indexed in Pubmed: 11837877.
  34. Frazão B, Vasconcelos V, Antunes A. Sea anemone (Cnidaria, Anthozoa, Actiniaria) toxins: an overview. Mar Drugs. 2012; 10(8): 1812–1851, doi: 10.3390/md10081812, indexed in Pubmed: 23015776.
  35. McIntosh JM, Jones RM. Cone venom–from accidental stings to deliberate injection. Toxicon. 2001; 39(10): 1447–1451, doi: 10.1016/s0041-0101(01)00145-3.
  36. Prator CA, Murayama KM, Schulz JR. Venom variation during prey capture by the cone snail, Conus textile. PLoS One. 2014; 9(6): e98991, doi: 10.1371/journal.pone.0098991, indexed in Pubmed: 24940882.
  37. Yotsu-Yamashita M, Mebs D, Flachsenberger W. Distribution of tetrodotoxin in the body of the blue-ringed octopus (Hapalochlaena maculosa). Toxicon. 2007; 49(3): 410–412, doi: 10.1016/j.toxicon.2006.10.008, indexed in Pubmed: 17188731.
  38. Fingerhut LC, Strugnell JM, Faou P, et al. Shotgun proteomics analysis of saliva and salivary gland tissue from the common octopus octopus vulgaris. J Proteome Res. 2018; 17(11): 3866–3876, doi: 10.1021/acs.jproteome.8b00525, indexed in Pubmed: 30220204.
  39. Bédry R, de Haro L, Bentur Y, et al. Toxicological risks on the human health of populations living around the Mediterranean Sea linked to the invasion of non-indigenous marine species from the Red Sea: A review. Toxicon. 2021; 191: 69–82, doi: 10.1016/j.toxicon.2020.12.012, indexed in Pubmed: 33359388.
  40. Wang Bo, Wang Q, Wang C, et al. A comparative analysis of the proteomes and biological activities of the venoms from two sea snakes, Hydrophis curtus and Hydrophis cyanocinctus, from Hainan, China. Toxicon. 2020; 187: 35–46, doi: 10.1016/j.toxicon.2020.08.012, indexed in Pubmed: 32871160.
  41. Kularatne SAM, Hettiarachchi R, Dalpathadu J, et al. Enhydrina schistosa (Elapidae: Hydrophiinae) the most dangerous sea snake in Sri Lanka: three case studies of severe envenoming. Toxicon. 2014; 77: 78–86, doi: 10.1016/j.toxicon.2013.10.031, indexed in Pubmed: 24239658.
  42. Kumar SS, Ragunanthanan S, Ramesh D, et al. Case reports of two interesting patients with sea snake envenomation. J Assoc Physicians India. 2020; 68(12): 78–81, indexed in Pubmed: 33247651.
  43. Kishida T, Toda M, Go Y, et al. Population history and genomic admixture of sea snakes of the genus Laticauda in the West Pacific. Mol Phylogenet Evol. 2021; 155: 107005, doi: 10.1016/j.ympev.2020.107005, indexed in Pubmed: 33160037.
  44. Tan CH, Wong KY, Tan KYi, et al. Venom proteome of the yellow-lipped sea krait, Laticauda colubrina from Bali: Insights into subvenomic diversity, venom antigenicity and cross-neutralization by antivenom. J Proteomics. 2017; 166: 48–58, doi: 10.1016/j.jprot.2017.07.002, indexed in Pubmed: 28688916.
  45. Lillywhite HB, Sheehy CM, Brischoux F, et al. Pelagic sea snakes dehydrate at sea. Proc Biol Sci. 2014; 281(1782): 20140119, doi: 10.1098/rspb.2014.0119, indexed in Pubmed: 24648228.
  46. Laustsen AH, Gutiérrez JM, Rasmussen AR, et al. Danger in the reef: Proteome, toxicity, and neutralization of the venom of the olive sea snake, Aipysurus laevis. Toxicon. 2015; 107(Pt B): 187–196, doi: 10.1016/j.toxicon.2015.07.008, indexed in Pubmed: 26169672.
  47. Fuehrer J, Kong EL, Murphy-Lavoie HM. Sea Snake Toxicity. StatPearls [Internet]. Treasure Island, Florida: StatPearls Publishing. 2021 Jan 11, indexed in Pubmed: 30422568.
  48. Watters MR, Stommel EW. Marine neurotoxins: envenomations and contact toxins. Curr Treat Options Neurol. 2004; 6(2): 115–123, doi: 10.1007/s11940-004-0021-8, indexed in Pubmed: 14759344

E.7 Vibration

Details

FROM SECOND EDITION BY DOMINIQUE JÉGADEN

Introduction

Mechanical vibration is a ubiquitous source of pollution on board ships. Vibration is defined as the variation over time in movement or position of a mechanical system, with an amplitude that is alternately larger and smaller than a reference value. The parameters involved in vibration are frequency of vibration (in Hertz/Hz), amplitude or displacement (m), speed (m/s), acceleration and direction of displacement (m/s2).

Some studies consider impedance, which is the dynamic force to which the structure is exposed over speed (Z = F/v  N s/m).

“Jerk” (m/s3) can also be defined as the derivative of acceleration with respect to time.

It is considered that:

- very low frequency vibrations correspond to frequencies of between 0 and 2 Hz

- low frequency vibrations correspond to frequencies of between 2 and 20 Hz

- high frequency vibrations correspond to frequencies of between 20 and 1000 Hz and more.     

They can be either continuous or periodic, and can occur randomly or transiently.

There are three types of conditions under which people are exposed to vibration:

  • Vibration transmitted to the whole body in all directions;
  • Vibration via the extremities, such as the hands, arms or head.
  • Vibration transmitted to the trunk via the lower limbs of a standing person, the pelvis of a seated person or the bed in the case of someone who is lying down.

The latter is the situation that is encountered on board ships, and therefore this is the focus of this chapter.

On board ships, personnel are subjected to whole-body vibration (wbv) on all three axes (horizontal, vertical and lateral). Acceleration is generally between 0.006 and 0.6 m/s2 along each axis in response to movements of the ship, and are very variable depending on sea conditions, wind direction and the position of the subject on board .

Given the complexity of the phenomenon, there are no satisfactory threshold exposure values. An evaluation of exposure of individuals to whole-body vibration is given in international standard ISO 2631.

Equivalent acceleration

Annoyance

Less than 0.3 m/s²

No discomfort

Between 0.3 and 0.6 m/s²

Slightly uncomfortable

Between 0.6 and 1.0 m/s²

Relatively uncomfortable

Between 1 and 1.6 m/s²

Uncomfortable

Between 1.6 and 2.5 m/s²

Very uncomfortable

More than 2.5 m/s²

Extremely uncomfortable

Relationship between various levels of discomfort and equivalent acceleration (ISO 2631-1:1997)

To evaluate the severity of vibration exposure, the acceleration equivalent (aeq) is calculated, which is the effective acceleration value measured at the point of entry into the body along the three orthogonal directions (x, y, z). The acceleration signal is weighted for frequency and direction in order to take into account human sensitivity to these parameters. An equivalent value over 8 hours (aeq(8h)) is obtained by multiplying the acceleration equivalent as measured by the square root of the ratio of daily actual exposure/8 hours.

In 2002 the EU adopted a Directive concerning minimum health and safety requirements regarding the exposure of workers to the risks arising from vibration. This Directive defines:

  • a level of exposure action value (EAV) set at aeq(8h) = 0.5 m/s2 over 8 hours. If this value is exceeded, employers are asked to assess and monitor the risks, to reduce vibration levels, to inform and train workers and to arrange health surveillance.
  • a daily exposure limit value (ELV) set at aeq(8h) = 1.15 m/s2, above which it is considered that regular exposure to vibration presents such a risk to health that vibration levels should immediately be reduced.

Vibration exposure on board ships

Vibration exposure on board sea vessels may arise from the following sources:

            - the propeller (periodic vibration)

            - the engine and ancillary machinery (periodic vibration)

            - the sea it self (random vibration)

Installation of ever more powerful propulsion systems on ships with high tonnage with a single driveshaft increases the discrepancy between the rigidity of the driveshaft and the flexibility of the ship’s structure. These phenomena have been responsible for increasing  vibration exposure on board ships. If two sources of excitation are close in frequency, a beat phenomenon emerges, and the frequency of this beat is likely to cause a resonant response.    

Structural factors

On ships, there are structures that resonate with forced vibration, for example:

            - the entire driveshaft, which is liable to respond laterally or longitudinally to excitation from the propeller or propulsion system, and thus in turn excites the structure of the double bottom;

            - the entity made up of a diesel propulsion engine and the structure of the double bottom that supports it. This entity responds to excitation in the form of forces and movements caused by the functioning of the engine, and is likely to make the structure of the hull vibrate.

Other “passive” resonators may be excited, such as the deck, partitions, mast, radar equipment etc.

The force transmitted from the propeller to the driveshaft causes vibration, and, in addition, the changes in the wake due to propeller actions, also influences the vibration of the driveshaft and pressure on the hull.

The fluctuations in the wake influences the propeller and the force the propeller transmit to the drive shaft as well as fluctuations in pressure on the hull. If cavitation occurs, the amplitude of pressure fluctuations on the hull will increase.

These fluctuations of pressure are linked to the following:

  • variations in propeller thrust: When the propeller provides thrust, the rear of each blade undergoes depression with respect to ambient pressure, and the front undergoes overpressure.
  • the number, surface area and thickness of the blades. Pressure fluctuation is a linear function of mean blade thickness and reduces rapidly as the number of blades increases.
  • presence of a variable pocket of steam on the surface of the blade and in its wake, as a result of Cavitation is responsible for most vibration problems found on board ships, following excessive pressure fluctuations on the rear underside. Cavitation is equivalent to an increase in blade thickness, and as such causes an increase in pressure fluctuations.

The fundamental frequency of propellers is around 20 Hz for fixed-blade propellers of between 5 and 6 metres in diameter, and 10 Hz for propellers between 8 and 10 metres in diameter.

If the response frequency of the propeller blades is very high (in the audible frequency range), “singing propellers” may be heard. This can be troublesome for the crew.

Engine vibration is caused by alternating piston/crankshaft motion. Excitation caused by free forces and moments within the engine can have an effect on the vibration response of the ship’s structure and even the girder structure, particularly in medium-sized ships with 2-stroke engines.

Engines generally vibrate at between 3 and 30 Hz.

The level of vibration depends, of course, on the type of engine, and particularly the engine speed.

Vibration caused by sea conditions

Vibration of the whole ship:

The swell causes random very low frequency vibration (less than 2 Hz) of the whole ship, both longitudinally (pitching) and transversely (rolling). The frequency of this vibration is between 0.01 Hz in very calm seas and 1.5 Hz in bad weather. It is generally between 0.1 and 0.3 Hz. Acceleration ranges between 0.005 and 0.8 m/s2, sometimes reaching 1 m/s2. These values vary depending on sea conditions and the position of the subject on board the vessel (Kingma) [1].

This vibration causes seasickness.

Ship girder vibrations caused by sea conditions:

These are usually considered to be of two types:

  • “Whipping”, which is caused by the hydrodynamic impact to the front of the ship, and which is a transient phenomenon that causes the ship girder to vibrate. Whipping usually occurs when the ship is forging ahead and when there is relative movement of the stem that is great enough to cause impact:
    • “slamming”, when impact occurs to a flat part on the bottom of the ship, when it falls back to the sea after emerging.
    • “slapping”, which occurs when there are impacts on the flat surface of the stem when it has not emerged from the water.
    • large waves (“green sea”).
  • “Springing”, which is created by excitation caused by variable hydrodynamic force created by the swell, and which is effectively a phenomenon whereby the ship’s girder is made to vibrate freely.

In conclusion: ships are environments in which significant stress is caused by vibration. Such vibration can be of very low frequency, of low frequency, and to a lesser extent high-frequency (range is between 0.01 Hz and 80 Hz, with a maximum of between 3 and 30 Hz). These vibrations can be periodic or random.

Fig x.x  Summary diagram of vibration on board ships

Health effects of ship vibration

Vibration and its effect on the human body.

The human body as exposed to vibration may be reduced to suspended elements (head, thorax, pelvis) linked by shock absorber systems (ligaments, muscles, intervertebral discs).

The physiological and psychological effects of vibrations on humans are caused by significant relative deformation and displacement undergone by organs and tissues at certain frequencies.

The frequency of the sinusoidal movement of a freely oscillating system if it is subject to impetus and not damped is known as the eigenfrequency (or natural frequency). The eigenfrequency of the organ corresponds to the maximum transmission of movement applied to it, if the organ is considered to be an undamped system. (A system with unrestricted motion.)  If the system is damped (which is generally the case in the human body), maximum transmission of movement occurs at a particular frequency which is known as the resonant frequency.  By definition, the resonant frequency is lower than the eigenfrequency, but there is generally only a small difference between the two, as the organs of the human body generally are not heavily damped.

Some resonant frequencies for a subject who is exposed to vertical vibrations:

  • Head: 20-30 Hz. Visual disturbance is also observed between 60 and 90 Hz, which can be explained by resonance of the eyeballs.
  • Thorax: 3-7 Hz. This explains the respiratory problems that are observed at such frequencies.
  • Heart: 4-8 Hz. Chest pains have been described, which could correspond to heart-related pain.
  • Abdominal and thoracic organs: 4 to 9 Hz
  • Spine: 2-6 Hz (5 Hz)
  • Pelvis: 4-9 Hz

At frequencies of less than 2 Hz, the body reacts like a single mass. In a seated human body, the first resonant frequencies occur between 3 and 6 Hz; in a standing human, there are two maximum values, at 5-6 Hz and 12 Hz (Subashi ) [2].

Resonance occurs when transverse or front-to-back vibration occurs at frequencies of around 2 Hz. It is caused by flexion in the lumbar and thoracic spine, in the hip joints and by curvature of the head.

The perception threshold for vibration is around 0.01 m/s2.

Vibration perception depends on:

  • the region and surface area of the body in contact with the source of excitation;
  • the intensity, frequency and direction of the vibration;
  • the subject’s sensitivity;
  • the position and posture of the subject and whether he/she is tense or relaxed;
  • the dynamic interaction between the body and the structure via which the vibration is transmitted to the human body;
  • the distribution, mass and dynamic properties of any clothes and equipment the subject may be wearing/carrying;
  • the environment: noise, temperature, lighting, vision;
  • the activity engaged in (physical, mental, visual, oral);
  • psychological influences.

A change in posture can alter distribution of body mass and resonance linked to vibration. This can also mean that vibration transmission shifts to another part of the body. The effects may, for example, be different for someone who is standing than for someone who is sitting. Muscular activity can modify the effects of vibration on the organism (Huang and Griffin) [3]. 

Seasickness (motion sickness)

Introduction

In general, seasickness occurs when there is a conflict between visual information and vestibular and proprioception information. There is a central difficulty in integrating the various sensory messages concerning body movement (this is addressed in Reason and Brand’s “sensory rearrangement theory” [4], or there is a conflict between the inner model and the outer reality.

Seasickness is triggered by very low frequency vibrations (0-2 Hz). Seasickness can be defined as a reflexive autonomic crisis that is linked to movement and that is triggered or worsened by vestibular hypersensitivity, autonomic nervous system irritability or psychological predisposition.

The conditions that determine whether seasickness will arise are the movements of the ship. Frequency and acceleration vary depending on sea conditions and the tonnage of the ship. The frequency of vibration ranges from 0.01 Hz in a very calm sea to 1.5 Hz in bad weather. Acceleration ranges from 0.01 to 0.8g and sometimes 1g.  Regular repetition and duration of movement should also be taken into account. A movement that is regularly repeated is more harmful than a sudden, irregular movement.

Seasickness was known as far back as Hippokrates, and the symptom of nausea derives its name from the greek word for boat (naus) [5].

The intensity and duration of symptoms can vary greatly between individuals, depending on the individual and on the type, duration and extent of movement. Especially nausea and vomiting are common in seasickness. Other symptoms - due to autonomic activation - are cold sweating, paleness and increased salivation. More general symptoms include headache, drowsiness, apathy, a vague feeling of illness, anxiety and reduced cognitive performance. Persons suffering from seasickness may be observed as clumsy and off balance, and in pain. There is marked pallor, the nose is narrowed and the blood pressure falls.

There is loss of psychological strength, which is significant and often disabling, with significant reduction in performance, reduction in muscular strength and co-ordination.

At the same time, it is important to be aware that for people in an occupational setting, symptoms may go unrecognized and be interpreted as fatigue or boredom rather than seasickness.

Conditions that increase seasickness:

  • Sleep deprivation
  • Strong odours: smoke, paint, fuel, perfume, vomit
  • Heat
  • Confined spaces
  • Athmospheric conditions can influence how seasickness develop
  • Movement; change of body posture
  • Psychological condition: excess emotion
  • Contagion: when one person is ill, the people around him/her often are as well
  • Apprehension and fear: memories of a bad voyage make seasickness more likely on future voyages.

A recent study has shown that the risk of nausea is at its greatest at around 0.2 Hz (Golding) [5].

Generally, symptoms resolve within the first 24 hours at sea. If the conditions persist, habituation develops relatively quickly, within 72 hours (finding one’s “sea legs”). Some people do not become habituated, and such people are unfit for sea travel.

In exceptional cases, complications arise: examples are dehydration, reduced blood pressure, ketoacidosis.

Pathophysiology of seasickness

 The pathophysiology of seasickness is fairly well-known. Balance is a complex system, and information is conveyed by three sensory faculties:

            - the vestibular system

            - the visual system, particularly as concerns tracking

            - the body’s proprioception system, particularly involving the feet and lower neck.

Such information is transmitted to nerve centres in the brain, where they are compared with each other and checked against previously stored information for coherence, which leads to a tailored balance response.

It is certain that seasickness originates in the vestibular system. People who are deaf because of inner ear destruction and animals without labyrinths do not experience seasickness. Very low frequency vibration is within the range of frequencies that activates vestibular receptors. This is not vestibular over-stimulation, but rather a problem with central integration of data that disagree with other receptors, and this causes the symptoms.

Ship roll seems to have a particularly marked effect on the semicircular canals, and pitching affects the otoliths.

It seems as though the central nervous system commits to memory sensory information that correspond to a particular movement situation. If signals from the various sensory receptors are compatible with this internal model, there is no problem. If there is a discrepancy, there are two consequences:

  • the internal model is reorganised: A typical example is known as "mal de débarquement" (disembarkment syndrome), which occurs when a subject returns from a period at sea and continues to experience an illusion of ship movement. Symptoms reduce with repeated travel. The occurrence of seasickness reduces greatly with practice. There seems to be a significant correlation between susceptibility to seasickness and mal de débarquement (Gordon) [7,8].Some authors, like Hain [9] and Nachum [10] make the distinction between several degrees of mal de débarquement: « landsickness » between 0 and 48 hours, mal de debarquement (MDD) between 48 hours and one month, persistent mal de debarquement (persistent MDD) if the condition lasts more than one month. The latter condition, which mostly affects women over 40, may last up to ten years. The unpleasantness of the condition can become quite disabling in such cases.
  • a sequence of autonomic nervous system effects is begun. Symptoms are caused by the length and intensity of the sensory conflict. O’Hanlon and McCauley [11] and Bles et al. [12] have put forward the theory that only vertical movement causes seasickness (the “subjective vertical conflict theory”), which incorporates the principle that it is the internal representation of gravity that is disrupted when sensory conflict arises. Most sensitivity seems to arise at 0.2 Hz. In an interesting study published in 1998, Wertheim [13] showed that although vertical movement (lift) is a necessary condition for seasickness, rolling and pitching also play an important role. In this study, thirteen men and nine women were exposed to different situations: while the group exposed only to rolling had just one case of seasickness, vertical movement alone caused no cases, but the incidence of seasickness climbed to 50% when the three components were combined. It seems to be head movements, directly connected with the combination of rolling and pitching along with lifting movement, that give rise to the notorious sensory conflict.

Current research on seasickness

Current research into seasickness seem to head in two directions: on the one hand, seeking increased understanding of susceptibility to the condition, and on the other seeking to model the circumstances under which it arises.  Although it has long been known that some individuals are susceptible to seasickness, very recent studies have attempted to achieve a better understanding of it. To this end, a questionnaire was developed: the Motion Sickness Susceptibility Questionnaire.  Buyuklu et al. [14] report that, in a population in whom this test was administered, 75% of subjects who were defined as being susceptible to motion sickness were prone to seasickness, 90% to carsickness, 10% to airsickness and 5% to simulator sickness, which suggests to me that this test is possibly not ideally suited to a maritime setting. 10% of those who were classified as not susceptible complained of seasickness in extreme conditions. The team also showed that there was a significant difference between men and women, and that women were more sensitive. A fairly recent (2009) study by Meissner’s German team [15] found, for example, that there was a significant difference between cortisol levels and susceptibility to motion sickness in men (not significant) and women (very significant). The second area of research is modelling to predict occurrence of seasickness in various parts of a ship, using impressive mathematical formulae processed using powerful computers. Concepts introduced include MSI (Motion Sickness Incidence), which is the percentage of passengers who vomit within two hours, the formula for which includes vertical acceleration among other variables, and VI (Vomiting Incidence) which is the probability of vomiting among a passenger population. The shape of the ship, its speed, centre of gravity, its moment of inertia, sea conditions and wave directions, the distribution of passengers and facilities on board, are also entered into the formula. Of course, all this comes under the heading of naval architecture, but we should take note of an interesting article by B Haward et al. [16] who studied the emergence of various seasickness symptoms in the crew of a supply boat, taking into account susceptibility to seasickness, ship movement, and also fatigue and sleeping problems. The problems became critical when vertical acceleration (again) exceeded 0.6 m/s2.

Prevention of seasickness

BY ALF MAGNE HORNELAND

Individuals react differently in how susceptible they are to seasickness. Some have history of seasickness that have interfered with their functional ability, whilst others have only experienced mild symptoms not interfering with their performance. Those with a significant seasickness tendency could be offered medication, whilst those with only mild symptoms should be counseled about adaptation to environmental factors.

General advice to all about adapation to the environment[1]:

  • Stay midships on lower deck, if possible
  • Look at the horizon, or focus on distant objects, if possible
  • Be involved with activities of steering if possible
  • Avoid reading or looking at a screen

Medication

  • Transdermal scopolamine applied behind the ear at least 4 hours before exposure has effect up to 72 hours, when it should be changed if there still is a need. Individuals with persistent symptoms could use a double dose[2]. Scopolamine is generally well tolerated, but could have side effects like sedation, blurred vision, dry mouth, and, in susceptible or old individuals, urinary retention and confusion. Scopoloamine has been demonstrated effective compared to placebo in a meta-analysis[3] .
  • Antihistamines have been widely used for prevention of sea-sickness, but they usually cause more sedation than scopolamine. Many different substances have been used, like diphenhydramine, clorpheniramine, cyclizine, cinarrizine, dimenhydrinate and meclizine[4] [5] [6]. Non-sedating antihistamines are not effective against seasickness[7] [8].
  • In refractory situations, when scopolamine or antihistamines do not produce the desired effect, promethazine has been used, but not much is published beyond anecdotal evidence. Oral scopolamine could be an alternative, but is not available in all countries. In some cases diazepam or phenytoin have been used with effect.
  • Combinations of a sedating antihistamine with a central stimulant (ephedrine, caffeine, and even amphetamine) is possible to use in cases where sedation must be avoided. Several combinations are available over-the-counter.

 

Treatment of seasickness

BY ALF MAGNE HORNELAND

If preventive measures have not been effective, and symptomatic seasickness occurs, it is a high likelihood that orally given medicines will not be absorbed as normal because of gastric stasis and vomiting. The parenteral route should be used for medication. One should continue to use the preventive measures mentioned above, and in addition promethazine injected intramuscularly or given as rectal suppository could be useful – 25 mg every four to six hours as necessary[9].

Other health problems associated with whole-body vibration (wbv)

Vibration can cause many different symptoms in the human body, like:

  • General discomfort and fatigue
  • Reduced performance which could lead to workplace incidents
  • Musculoskeletal disease
    • Low back pain
    • Neck- and shoulder problems
    • Herniated discs
    • Early degeneration of the spine
  • Cardiovascular
  • Respiratory problems
  • Neurological effects
  • Endocrine and metabolic changes
  • Reproductive organ damage
  • Impairment of vision and balance
  • Increased nose-related hearing loss as compared to noise-exposure alone

A number of factors can increase the health effects in the human body, like prolonged sitting in constrained or poor postures, frequent twisting of the spine, twisted head postures, cold work temperatures and stress. Workplace design and task/work organization can influence the effects of exposure to whole-body vibration.

FATIGUE AND SLEEPING PROBLEMS

Along with seasickness, Haward et al [16]. have shown that fatigue and sleeping problems are strongly correlated with movement along all three axes, and the strongest correlation is with sleep quality. Hours spent asleep were negatively correlated with amplitude of movement.

On board ships, vibration of between 2 and 20 Hz is found, and as we have seen this is linked to the propulsion system and propellers. The intensity of this vibration is generally quite low. Depending on the RPM of the engine, this vibration can be amplified and, if this occurs, inconvenience is caused to those trying to write or read. This can also cause partitions to resonate, and can generate unpleasant noise which will increase general fatigue and exacerbate concentration problems. Many authors have attempted to quantify the reduction in performance experienced by people exposed to periodic and random vibration. Vibration makes a task more difficult and cumbersome. Vibration hampers precise movement and accurate prehension with hands and fingers.

Vibration also leads to an increase in reaction time, requiring greater concentration on the task in hand at the expense of attention to secondary tasks, which means that vigilance is reduced.

SPINE AND LOW BACK PAIN

Lower back pain is also associated with an increase in amplitude of ship movement. Törner et al. [17, 18] have reported that vertical acceleration of ±0,4m/s² and rolling of ±8 degrees on board trawlers is associated with an increase in cerebrospinal fluid pressure. Hoogendoorn's [19] work suggests that twisting movements of the spine are an independent factor responsible for lower back pain. Such movement is common on board as individuals seek to keep their balance as the ship moves, particularly on board small vessels. However, Törner has shown that knee movement acts as a buffer. In spite of this, compression forces may be increased while carrying materials on board, because of increased contraction when attempting to stabilize (Barzgari) [20]. Several authors (Törner) [18], (Wertheim) [21] have shown that oxygen consumption was increased in subjects standing on board ships while undertaking a lifting task, but that oxygen exchange was reduced, because of overall muscular tension, which increases fatigue levels. Conversely, Drerup [22] found no abnormalities in intervertebral discs in subjects exposed to whole-body vibration, in comparison with a control group.

In a subject who is exposed to this type of vibration, shifting body mass and maintaining posture (particularly in the case of random vibration such as whipping and springing jerks) leads to stimulation of muscular activity which compensates for the effects of vibration. If there are major jerks (acceleration greater than 2 m/s2), there can be trauma to the lower back, in the form of fractures or compression injuries, particularly to L3-L4 (Ayari) [22].

Holmlund et al.[23] have shown that impedance increases as a function of frequency, up to an initial maximum in the 4-6 Hz range, which particularly affects the spine. There is a second and third impedance maximum in frequency ranges 8-12 and 50-70 Hz.

Subjects exposed to medium-frequency whole-body vibration have been shown to have a higher incidence of lower back pain (Burdorf) [24].

Vibration can lead to microscopic trauma of the spine, particularly the lumbar spine, which are particularly troublesome because the spinal column is unbalanced. On board ships, particularly fishing vessels, vibration is a factor that exacerbates problems caused by postural constraints and the difficulty of keeping one’s balance in a moving vessel, as we have seen. The most significant responses were in the 5-8 Hz range.

RESPIRATORY SYSTEM

Low-frequency vibrations, particularly between 4 and 12 Hz, tend to increase respiratory parameters: respiratory frequency, ventilation rate and oxygen uptake (Maikala) [25]. These increases seem to be linked to general muscular tension caused by vibration: at 10 Hz, there is very significant tension in the muscles in the lower back, chest, abdomen and back.

 CARDIOVASCULAR EFFECTS

An increase in heart rate is often observed. Between 4 and 11 Hz, when vibration is of significant intensity, disturbances to heart rhythms have been observed, in the form of extrasystoles and at times tachycardia.

Occasional cases of myocardial infarction in young people with no history of arteriosclerosis or coronary artery disease, have been linked to vibration.

DIGESTIVE AND URINARY TRACT

Digestive tract and urinary tract problems have also been observed, which are partly due to changes in peristalsis in visceral smooth muscle.

This all has an effect on general levels of fatigue, which are already raised by various causes (noise, very low frequency vibration, stress etc). 

LOCAL EFFECTS – HAND/ARM VIBRATION SYNDROME (HAVS)

High-frequency vibrations, above 20 Hz, have a purely local impact. The most commonly studied example of this is vibrating tools. Some seafarers (engineers or deck crewmembers) are likely to use such tools, for rust removal, sanding and cutting. Upper limb conditions arising from such vibration are well known. High-frequency vibration can cause angioneurotic problems in the hands and fingers, arthritis in the elbows and finger joints, bone disease in the carpal bones (necrosis of the lunate bone or Kienböck’s disease). These diseases are rare in seafarers, but it is nonetheless essential that the field of maritime medicine gain familiarity with them in order to diagnose and prevent them.

Bibliography

  • Kingma I, Delleman N, Van Dieën J. The effect of ship accelerations on three-dimensional low back loading during lifting and pulling activities. International Journal of Industrial Ergonomics 2003; 32: 51-63
  • Subashi G, Matsumoto Y, Griffin M. Modelling resonances of the standing body exposed to vertical whole-body vibration - Effects of posture. Journal of Sound and Vibration 2008; 317: 400-48
  • Huang Y, Griffin M. Nonlinearity in apparent mass and transmissibility of the supine human body during vertical whole-body vibration. Journal of Sound and Vibration 2009 forthcoming,
  • Reason JT, Brand JJ. Motion sickness. London, Academic Press, 1975
  • com, Motion sickness, literature review current through May 2021.
  • Golding JF, Mueller AG, Gresty MA. A motion sickness maximum around the 0,2 Hz frequency range of horizontal translational oscillation. Aviat Space Environ Med 2001; 72: 188-92
  • Gordon CR, Spitzer O, Doweck I, Melamed Y, Shupak A. Clinical features of mal de debarquement: adaptation and habituation to sea conditions. J Vestib Res 1995; 5: 363-9
  • Gordon C, Spitzer O, Shupak A, Doweck I. Survey of mal de debarquement. BMJ 1992; 304: 544
  • Hain T, Hanna P, Rheinberger M. Mal de debarquement, Arch Otolaryngol Head Neck Surg 1999; 125: 615-20
  • Nachum Z, Shupak A, Letichevsky V, Ben-David J, Tal D, Tamir A et al. Mal de debarquement and posture - reduced reliance on vestibular and visual cues.
  • O’Hanlon J, Mc Cauley M. Motion sickness as a function of the frequency and acceleration of vertical sinusoidal motion. Aerospace Medicine 1974; 45: 366-9
  • Bles W, Bos J, de Graaf B, Groen E, Wertheim A. Motion sickness - only one provocative conflict? Brain Research Bulletin 1998 ; 47: 481-7
  • Wertheim A. Working in a moving environment. Ergonomics 1998; 41: 1845-58
  • Buyuklu F, Tarban E, Ozlioglu L. Vestibular functions in motion sickness susceptible individuals. Eur Arch Otorhinolaryngol 2009; (published online 26 February 2009)
  • Meissner K, Enck P, Muth E, Kellermann S, Klosterhalfen S. Cortisol levels predict motion sickness tolerance in women but not in men. Physiology & Behavior, in press 2009
  • Haward B, Lewis C, Griffin M. Motions and crew responses on an offshore oil production and storage vessel. Applied Ergonomics 2009 in press.
  • Törner M, Blide G, Eriksson H, Kadefors R, Petersén I. Musculo-skeletal symptoms as related to working conditions among Swedish professional fishermen. Applied Ergonomics 1988; 19 (3): 191-201
  • Törner M, Almstrom C, Kadefors R, Karlsson R. Working on a moving surface – a biomechanical analysis of musculoskeletal load due to ship motions in combinations with work. Ergonomics 1994; 37(2): 345-62
  • Hoogendoorn W, Bongers P, De Vet P, Douwes M, Koes B, Miedema M et al.Flexion and rotation of the trunk and lifting at work are risk factors for low back pain: result of a prospective cohort study. Spine 2000; 25: 3087-92
  • Bazrgari B, Shirazi-Adl A, Kasra M. Computation of trunk muscle forces, spinal loads and stability in whole-body vibration. Journal of Sound and Vibration 2008; 318: 1334-47
  • Wertheim A, Kemper H, Heus R. Maximal oxygen uptake during cycling is reduced in moving environments: consequences for motion-induced fatigue. Ergonomics 2002; 45: 186-202
  • Drerup B, Granitzka M, Assheuer J, Zerlett G. Assessment of disc injury in subjects exposed to long-term whole-body vibration. Eur Spine J 1999; 8: 458-67
  • Ayari H, Thomas M, Doré S, Serrus O. Evaluation of lumbar vertebra injury risk to the seated human body when exposed to vertical vibration. Journal of Sound and Vibration 2009; 321: 454-70
  • Holmlund P, Lundström R, Lindberg L. Mechanical impedance of the human body in vertical direction. Appied Ergonomics 2000; 31: 415-22
  • Burdorf A, Hulshof C. Modelling the effects of exposure to whole-body vibration on low-back pain and its long-term consequences for sickness absence and associated work disability. Journal of Sound and Vibration 2006; 298: 480-91
  • Maikala R, King S, Bhambhani Y. Acute physiological responses in healthy men during whole-body vibration. Int Arch Occup Environ Health 2006; 79: 103-14
  • Lackner JR. Motion sickness: more than nausea and vomiting. Exp Brain Res (2014) 232:2493–2510

 

[1] Bos JE, MacKinnon SN, Patterson A. Motion sickness symptoms in a ship motion simulator: effects of inside, outside, and no view. Aviat Space Environ Med 2005; 76:1111.

[2] Bar R, Gil A, Tal D. Safety of double-dose transdermal scopolamine. Pharmacotherapy 2009; 29:1082.

[3] Spinks A, Wasiak J. Scopolamine (hyoscine) for preventing and treating motion sickness. Cochrane Database Syst Rev 2011; :CD002851.

[4] Buckey JC, Alvarenga D, Cole B, Rigas JR. Chlorpheniramine for motion sickness. J Vestib Res 2004; 14:53.

[5] Brand JJ, Colquhoun WP, Gould AH, Perry WL. (--)-Hyoscine and cyclizine as motion sickness remedies. Br J Pharmacol Chemother 1967; 30:463.

[6] Lucertini M, Mirante N, Casagrande M, et al. The effect of cinnarizine and cocculus indicus on simulator sickness. Physiol Behav 2007; 91:180.

[7] Kohl RL, Homick JL, Cintron N, Calkins DS. Lack of effects of astemizole on vestibular ocular reflex, motion sickness, and cognitive performance in man. Aviat Space Environ Med 1987; 58:1171.

[8] Cheung BS, Heskin R, Hofer KD. Failure of cetirizine and fexofenadine to prevent motion sickness. Ann Pharmacother 2003; 37:173.

[9] Davis JR, Jennings RT, Beck BG, Bagian JP. Treatment efficacy of intramuscular promethazine for space motion sickness. Aviat Space Environ Med 1993; 64:230.

E.2 Application of risk management principles to work-related health risks

Details

TIM CARTER 

Further information on the principles of health risk management is available in Ch xxx

Risk assessment

The health effects of many hazardous agents are well known. In some cases such as noise or commonly used chemicals they have been quantified through studies in onshore populations. These results can be extrapolated, with care, as guides to the risk on board. In some cases, information supplied with items of equipment or chemical products (material safety data sheets) provide practical guidance on necessary precautions. These sources sometimes give recommendations on acceptable levels of exposure.  However, information is not always available, particularly on the risks from bulk cargoes in confined spaces or on cleaning operations. In addition, the effect of some complex exposures, for instance welding fumes or flue gas mixtures, will vary markedly depending on circumstances.


A valid risk assessment takes account of both the inherent hazards of the agents present and of the levels and frequency of exposure to them. Where there are uncertainties about hazards, expert assistance may be needed. Where there is uncertainty about exposures then measurements may need to be made. Often a single risk assessment document can be produced that is applicable to a particular operation wherever it is carried out.

Control measures

The outcome of the risk assessment will include a number of measures that need to be applied. This will normally be based on the hierarchy of control approach with the preferred option being the elimination of risk, while the last resort is the use of personal protective equipment. For such measures to be effective, those who could be at risk need to be made aware of the reasons for taking precautions and of their detail. Supervision is required to ensure that all control measures are followed.

More information is available in Ch xxx.

Monitoring

Where risk is significant, measurements of ambient exposure levels may need to be taken. If the risk is immediate, techniques such as using gas detection devices may be appropriate. Direct reading instruments are also useful for longer-term risks such as noise as they show where levels may be dangerous. Often shift long measurements of cumulated exposure are appropriate as many of the limit values for acceptable exposure are given as eight-hour averages.
For some chemical substances it is possible to measure uptake using breath, blood or urine samples from those exposed. However, these are rarely useful as routine in maritime settings, unless there is immediate access to laboratory support as well as to expertise in the interpretation of results and to knowledge on the ethical aspects of responding to the findings.

Health surveillance

Where the early detection of harm can prevent it becoming more serious, assessment of pre-clinical or early signs of damage can help the seafarer to make personal decisions or receive advice from a health professional on future career options.  Equally important is the use of any results from surveillance as evidence on whether there are shortcomings in the risk assessment and risk management. Often information from a group of exposed workers needs to be analysed. Health surveillance, except at its simplest level, such as skin inspections in those working with irritants, is shore-based.

 

Review of risk assessment and risk management

Reports from supervisors, workers’ concerns, the results of monitoring and health surveillance all need to be reviewed periodically to decide if the precautions in place are adequate. At the same time, suppliers’ information and scientific literature needs to be checked to ensure that there is no new information on the hazard and its risks. If shortcomings in precautions have been detected it may be appropriate to make this information widely available so that others can benefit from it.

E.1 Seafarer Injury and Illness

Details

TIM CARTER

Introduction

Chapter xx provides an overview of the principles of maritime risk management. This chapter focuses on the various types of harm to the health and well-being of seafarers that may arise as a consequence of working and living at sea.  The harms considered are those where good risk management can reduce the frequency and severity.

For  risks that are directly attributable to tasks at work there is a clear obligation on the employer to have adequate precautions in place, normally formalised as part of the statutory Safety Management System (SMS). For others, such as certain illnesses and mental distress, where living conditions at sea may be a contributor, there are fewer formal requirements, but it is both useful and good practice to have effective preventative measures in place.

Most types of risk and their control measures are considered in the sections that follow. Other chapters provide information that relates to certain aspects of health risk management:

  • Infectious disease risks (xx).
  • Management of casualties and from illness at sea (xx)
  • Risk reduction by crew selection (xx)
  • The human element

Injuries and illnesses compared

Injury is almost always a direct effect of energy of some sort interacting with vulnerable parts of the body. Most commonly this is gravity, whether causing a fall or causing an item to fall on a person. It may also be the kinetic energy of a sharp or fast moving object. Less common causes include heat (burns) or electrical energy (burns or electrocution).  Corrosive chemicals can also directly destroy tissues.  An injury event can easily be defined by time and place and it is then possible to work back from this to establish the contributory causes of the injury and how they relate to each other.

By contrast the external causes of illness present a challenge to the biological processes of the body, which are not always able to respond to them and so become damaged. It is for this reason that harm sometimes only becomes apparent long after exposure, although occasionally it may be immediate, as with exposure to an acutely toxic substance such as carbon monoxide. This delay may be because the harm is the effect of cumulative exposure over a long period, as in deafness caused by noise, or because effects can take many years to become apparent, such as in the case of cancers. Processes may be reversible if identified early enough to reduce exposure or to treat the early stages of harm. The same biological process may be upset for several different reasons, some external and some inherent in variations between individuals.  These features mean that harm to health usually has to be searched for, unless the effect is immediate, rather than becoming apparent in a similar way to an injury. Also if the harm is long-term then it may only be visible after a seafarer has ceased to work at sea and follow up may be needed.

Living at sea and ill-health

Most ill-health in seafarers is not directly related to work tasks. Patterns of disease tend to follow those in the seafarer’s home country. However living at sea may modify this pattern, for instance because of dietary changes, hours of work and rest, mental stresses, lack of opportunities for exercise and personal habits, such as smoking or substance abuse. For these sorts of lifestyle associated risk the style of prescriptive risk management that is acceptable for injury and work-related disease prevention is inappropriate. The emphasis needs to be on health promotion activities that give the individual insights such that they decide to change their behaviour. However, this may need culturally sensitive but active support from shipping management, for instance by the provision of the components of a healthy diet, exercise facilities and policies on smoking.

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E.3 Injury risks

Details

TIM CARTER, CONTRIBUTIONS FROM BOB BRIDGER; MARGARETHA HOLTENSDOTTER LÜTZHÖFT AND VIVEK MENON

Introduction

Seafarers and especially those working on fishing vessels are at a considerably greater risk of injury than those working ashore. This section reviews the major causes of injuries at sea and identifies some of the preventative measures that are available. The problems of managing injuries at sea are also considered.

This section does not set out to be a comprehensive review of injury at sea. Its aim is to give readers an overview to enable them to participate in discussions and joint problem solving with others working in this field.

Sources of data on injuries in seafarers and their limitations.

Merchant Shipping

Injuries

Event reports are the usual source of information about injuries. These may be required by maritime accident investigation authorities or by ship operators or their insurers. Case reports can be valuable if a case has been investigated in detail and lessons from it identified. Maritime accident investigators in a number of countries produce such case reports, either as a result of their investigations into a major incident or as summaries of the event reports they receive.  Companies or insurers may do the same, although the latter often have more information about the financial consequences of an event, than about causation. Academic investigators may mount studies of injury incidence and causation but most of the available data comes from official sources such as maritime authorities.

The source data on injuries is heavily dependent on assiduous reporting by ship’s officers, with or without the prompting of seafarers or their safety representatives. There can be situations, such as company incentive schemes for safety performance that encourage under-reporting.  Considerations about insurance or compensation may also lead to the miss-attribution of the cause of an injury to a non-controversial one, rather than one that the ship operator may have to assume liability for. Individuals may also not report injuries for fear of criticism or a threat to their job.[i]

The pattern of reports is dependent on the criteria for inclusion, for instance which locations are covered, and the reporting criteria used: fatal, requiring hospital admission, unable to work for more than three days etc. Measures of incidence also need to be analysed separately from measures of the duration of incapacity. Incidence measures depend on the reliable documentation of the population at risk; something that is difficult with mobile populations like seafarers or those who are self-employed and often only work of a limited number of days a year, such as fishers. [ii] These population measures need to be handled with caution as a seafarer will spend part of their day working and exposed to one pattern of injury risks, another part on board but still adjacent to the workplace and with some time engaged in work tasks in port. Additional information can be found in Ch xxx.

 

Fatal accidents   

Fatal accidents in merchant seafarers are the subject of statutory notification procedures in many countries and most investigations have used such information as the basis for their analysis. Probably the longest series of consistent analyses come from the UK, where the rate of fatal accidents in merchant seafarers dropped from 208 per 100,000 person years in 1921 to 11 per 100,000 in 1996-2005.[iii] During this time, ships, and therefore risks, changed hugely. Around 50% of fatalities in most studies arise from ship disasters.[iv] There are large differences in reported fatality rates between countries and much of this is likely to be explained by different inclusion criteria for reporting. For example, whether fatalities while travelling to or from work are included. Fatality rates among seafarers are far higher than the average for onshore workers, sometimes as much as 10 times.[v]

Studies of non-fatal injuries use data from a variety of sources, for example, statutory notifications, insurance claims and company records. The downward trend is less clear than for fatal accidents, and most studies are essentially limited to personal injury records, excluding ship disasters. Confidential near miss reporting systems can also provide important information on the nature and frequency of situations that have the potential to lead to injury or damage.[vi]

Ratings usually have a considerably higher incidence of injuries than officers do.[vii] As on land, slips, trips and falls are major causes of injury, with movement between ship and shore a significant contributor.[viii] Human factors, notably fatigue, are probably just as important antecedents to personal injuries as they are to ship disasters.

 

Fishing

Injury rates are generally even higher in the fishing industry than in merchant seafarers. The industry uses a huge range of vessels, from large factory trawlers to dugout canoes. Each type of vessel and method of fish catching has its own pattern of injury risks.[ix] Factors such as weather, water temperature and the presence of harmful or predatory marine life also influence these risks. Fishing is consistently shown to be among the highest risk of industries and more information on the fishing industry can be found in Ch xxx.

Fatality rates in developed countries, mainly in NW Europe where most studies have been conducted, have reduced in recent decades.[x] Around half of all fatalities were attributable to vessel disasters. Some of these were a consequence of instability either from unsafe modifications or from fishing activities. However, it is likely that human factors and especially fatigue, which is commonly at high levels in fishing crews, are major contributors.[xi]

Unfortunately, there is no available evaluation of risks on the large number of boats in use in the developing world that are almost certainly less safe.  However, it is clear that fishing everywhere has a high risk of accidents and that there is considerable scope for better prevention, given the resources and will to intervene.

Fish farming has its own pattern of injuries, some from the use of small boats and some from diving incidents but the introduction of effective risk management strategies has been shown to be effective. For example in Alaska, fatal accident rates fell from 4.2 per 1,000 person years in 1980-4[xii] to 1.16 in 1991-8[xiii]. During this period part of the fleet was renewed with larger, safer vessels and better personal protection including immersion suits with radio beacons were introduced. These provide built in insulation and buoyancy and aid location of the casualty.

6.3.2.4     Summary of information on injury risks

  • Seafarers have high overall rates of injury compared with most other occupations, with fishing as the most extreme.
  • Vessel disasters, occupational injury and injury in non-occupational settings all contribute to the total.
  • The available data are limited, with none from other than developed countries with established maritime regulation and academic centres
  • There are problems of comparability because of different recording criteria
  • There are very few follow up studies to explore the consequences of injury for the person affected, their rehabilitation and subsequent working ability.

 

Injury causation

BOB BRIDGER, MARGARETHA HOLTENSDOTTER LÜTZHÖFT

The final release of energy leading to an injury is the last stage in a chain of events. There are a number of approaches to the analysis of causes in widespread use and which are applicable to maritime settings. Some are concerned with attributing blame or liability for the event, others are tools that can aid the understanding and analysis of the events leading up to the injury with the aim of prevention and others are used as a theoretical basis for approaches to prevention.  These are noted here because other professional groups commonly use them and familiarity with them will aid discussions.

  1. Swiss cheese model (Reason) http://en.wikipedia.org/wiki/Swiss_cheese_model
  2. Haddon’s matrix
    http://en.wikipedia.org/wiki/Haddon_Matrix
  3. Fault tree analysis
  4. http://en.wikipedia.org/wiki/Fault_tree_analysis
  5. Hazam and hazop studies http://en.wikipedia.org/wiki/Hazard_and_operability_study
  6. Heinrich’s triangle http://en.wikipedia.org/wiki/Herbert_William_Heinrich
  7. The iceberg effect – safety economics //www.ilo.org/wcmsp5/groups/public/@ed_protect/@protrav/@safework/documents/publication/wcms_110381.pdf">http://www.ilo.org/wcmsp5/groups/public/@ed_protect/@protrav/@safework/documents/publication/wcms_110381.pdf
  8. Safety culture and behaviourhttp://en.wikipedia.org/wiki/Behavior-based_safety

 

Injury prevention and risk management on board ship. Health related aspects

The principles of preventing navigational errors leading to ship disasters such as grounding or collision are beyond the scope of this book.   More information on ship incidents is available in Ch xx. The specific contributions of health professionals in preventing such events includes:

  • responsibility for assessing the medical aspects of fitness for those undertaking safety critical duties as well as for identifying those likely to have an excess risk of injury associated with the strains of prolonged periods of work at sea.
  • advice on human factors aspects of navigation, for example, the visual requirements and the task demands of work on a ship’s bridge.
  • recommendations on crewing levels to avoid problems such as fatigue and insufficient time for safe handover between watches.

The prevention of work related injury to individuals at sea is based on similar risk assessment approaches to those adopted ashore. Such work needs to be based on an assessment of hazards and risks in the working environment, and the implementation of steps taken to mitigate them. Further information is available in Ch xx. Practical difficulties arise because of the conditions at sea, with moving decks, slippery surfaces and unguarded or enclosed spaces. Another feature is the command structure on board. This can lack the separate safety supervision functions that are common elsewhere. Hence the safety culture on board will be heavily dependent on that adopted by a few senior officers. They are likely to be under economic and operational pressures that may count against ensuring that precautions and training are adequate. In addition, where crews are multi-cultural, different sub-groups may each have their own conceptions of risk and safety that may be incompatible.

When injuries arise at sea, there is usually no immediate access to specialised treatment facilities. Maritime disasters may require evacuation of a ship using lifeboats or other aids and this can lead to the risk of hypothermia and drowning. Modern evacuation systems go some way towards minimising such risks but, particularly in the safe evacuation of passengers, some of whom may have mobility and other limitations, physical strength and a positive psychological attitude are important. Here health professionals may play a part in determining criteria that will ensure that seafarers are capable of such tasks.

The shipboard environment

Other emergencies such as a fire on board or loss of power, place high physical and psychological demands on crew. In these situations, the ship will be entirely dependent on the training and capabilities of those who undertake such tasks. Firefighting often requires the use of breathing apparatus that is heavy and where the duration of the air supply will depend on breathing rates that are usually higher in the unfit, the overweight and those who are highly anxious. Fitness criteria used at selection, or more practically meeting the demands on a firefighting training course are important ways of reducing the risk of inability to respond in an emergency.

Non-working time may also be taken at sea and here there are a range of more domestic risks, such as sports injuries, falls and burns from food preparation.  Onshore injury risks while in port or during leave periods may also be domestic in character, but their frequency may be raised by the use of alcohol and the location of the vessel in a hazardous harbour area. Inadequate arrangements for access to vessels, especially fishing vessels, are a significant cause of injuries in port.

Occupational injuries in fishing are a particular problem because of the conditions of work, including

  • deck based casting and hauling of gear,
  • the congested presence of fast moving and heavy cables, beams and weights as well as the winches used to move them.
  • the small size of the vessels meaning they respond rapidly to sea conditions
  • slippery decks from fish and other marine debris.

 

Common Maritime Injuries

VIVEK MENON

Below are examples of some commonly encountered injury risks that have specific maritime features. Almost all of the range of injuries encountered ashore can also occur at sea, from eye injuries from flying projectiles when paint chipping or hammering, through knife wounds in the galley during food preparation, to falls from bed in rough weather. The feature common to all is the difficulty of access to treatment and care whilst at sea, and hence a higher risk of long-term adverse outcomes than may be the case ashore. Additional information on medical care at sea can be found in Volume xx.

Slips, trips and falls

The surfaces of a vessel may be wet, slippery, cluttered, moving and uneven. All these features increase the risk of slips and trips, which will commonly lead to falls to deck level. If they occur at an unguarded edge, such as the side of the vessel, an open hold or access opening on a container, or at the top of a companion way(flight of stairs), they may result in a fall from a height that is likely to result in severe injury.

Person(s) overboard

Falls from a vessel or between a ship and a quayside carry the additional risks of hypothermia, drowning and crushing, as does being swept off the deck by the sea. Rescue can be complex and involve other crewmembers in the risks of launching a boat and picking up the person. This is a particularly common risk in fishing as gear is handled over the side of the boat and, should entanglement occur while it is being run out, there is a risk of being drawn overboard with it. Historically, many of the falls between ship and quay arose when seafarers returned to a vessel when affected by alcohol.

Falling and swinging objects

A ship is a multi-layered environment, where activities on upper decks, masts or derricks can pose risks to those below if, for instance, tools are dropped or if lifting gear is swinging. Such risks are particularly common during cargo handling as loads are lifted and moved or fastenings are attached.

Work in enclosed spaces

Enclosed spaces may pose risks from their lack of access and ventilation. They include cargo areas, such as the tanks on a liquid bulk carrier or spaces adjacent to cargoes that change the composition of the air. Spaces in the body of the ship, such as fuel stores, chain lockers and access routes to inspect the extremities of the hull pose similar risks. Atmospheres may be inflammable or explosive, deficient in oxygen or contaminated with toxic gasses. Hence, fire, explosion, asphyxiation and poisoning can arise. Additional information on chemical risks is available in Section xxx.. If a person is harmed in an enclosed space, it can be a complex and dangerous task to remove them.

Work on board in enclosed spaces is an important and largely avoidable cause of serious and fatal injuries, sometimes involving more than one worker or harming inadequately protected rescue personnel who enter a space to try and help someone in distress.  Detailed methods for safe working practice have been published by IMO and industry bodies.[1][2] These cover aspects such as:

  • gas freeing and testing the atmosphere in space for toxic or fire risks and to detect low levels of oxygen
  • protective clothing
  • breathing apparatus use
  • permits to work to ensure that new hazards are not created when work is in progress
  • back up and supervision to identify is a person who has entered the space is distressed from working conditions, injury or sudden illness
  • arrangements for safe rescue if problems arise, including immediate access to protective clothing and breathing apparatus.

Acute chemical incidents

Chemical substances, both in cargo and those used on board as cleansing agents, scale removers and solvents, can cause acute injury. This may be by inhalation (gassing), often in a confined space, by corrosion of the skin and in particular by damage to the eyes. Additional information on the risks of chemical substances can be found in Ch xxx.

Burns and electrical injuries

The commonest locations for thermal burns to occur on board are in the engine room, and they usually result from flames, explosions or scalding and in the galley, where they result from contact with hot fluids or objects during cooking.

Chemical burns from corrosives have many of the same features as thermal ones.

Electrical injury will be associated with power generation and use.

Work in port and other manual handling tasks

The risks of slipping, tripping, falling and being struck by objects have already been noted. Some types of cargo handling such as securing containers are known to pose a high risk. Despite mechanical aids there is still much manual handling. Tasks include the movement of warps and springs when mooring, the loading of food and other requirements that are not done by the main cargo handling equipment. Movement of hatch covers may also involve hard physical work. Much of the damage is long term, but sudden strains and unexpected movements can cause acute musculoskeletal injury. More information on musculoskeletal injures can be found in Ch xx.

Hawsers and winches

Both merchant and fishing vessels make extensive use of ropes, cable and hawsers. Particular risks include the parting of a hawser, especially a steel one, where the broken end may move around with high velocity, unspinning as it moves. This can result in major injuries to those who are in its path.

Where cables are being winched in or out there will be pinch points between the winch or capstan and the coiled cable. These are often close to the locations where a crewmember is positioned, and part of their task may be to ensure that the cable coils correctly – with the temptation of intervening by hand in the event of a problem leading to hand and finger injuries. Such incidents are particularly common with the repetitive hauling tasks in fishing, often undertaken by tired seafarers on a slippery and congested deck.

Fishing injuries and poisonings

Personal injuries in fishing have many causes. A number have already been referred to. There is a high incidence of hand injuries; from fishing gear, marine debris and knives used in gutting. Because the hands are often wet for prolonged periods, infection of injuries is common and a number of unusual or sea-specific pathogens may be present. Fishhooks readily penetrate the skin and, because they are on lines, can reach most parts of the body.

A number of sea creatures have defensive spines, and these can cause penetrating injuries. Some inject venom and this can lead to local or generalised toxic reactions. More information on dangerous aquatic organisms can be found in Ch xxx.

The postures adopted to perform tasks and maintain stability on small fishing vessels can lead to acute or long-term musculoskeletal injury.

Diving accidents in crew doing ship inspections

Diving to inspect and maintain a ship may be undertaken by a specialist contractor or by a crewmember who has, often limited, training and skills as a diver. Common tasks include freeing debris from rudders and propellers and inspecting for damage after grounding or collision. In addition to the normal risk from diving, there are particular risks that arise from being adjacent to a ship, especially in adverse weather conditions. Sea movements may result in rapid changes in position leading to harm from contact with the ship, potentially rapid pressure changes, disorientation and severe lacerations from the propellers from the boat used for diving or from other vessels. Crush injuries may also occur when diving between vessels or between the vessel and a fixed jetty or quay. More information on diving is available in Ch xxx. 

[1] https://www.westpandi.com/publications/news/imo-revised-recommendations-for-entering-enclosed/

[2] https://www.ics-shipping.org/wp-content/uploads/2020/08/document-b-guidance-on-enclosed-space-entry-and-rescue-based-on-ics-tanker-safety-guide-chemicals28F7B3075079.pdf

[i] Conghua Xue. Safety Aboard Chinese Vessels. In Gekara O, Sampson H, editors.The World of the Seafarer:Qualitative Accounts of Working in the Global Shipping Industry, Springer Link, 2021. pp 127-139. https://link.springer.com/book/10.1007%2F978-3-030-49825-2 accessed 9th June 2021.

[ii] Carter T. Mapping the knowledge base for maritime health: 2.a framework for analysis. Int Marit Health. 2011;62:217-233.

[iii] Roberts SE. Fatal work-related accidents in UK merchant shipping from 1919 to 2005. Occup Med (Lond.). 2008;58:129-137.

[iv] Roberts SE,  Hansen HL. An analysis of the causes of mortality among seafarers in the British merchant fleet (1986-1995). Occup Med (Lond.). 2002; 52: 195-202

[v] Hansen HL, Pedersen G. Influence of occupational accidents and deaths related to lifestyle on mortality among merchant seafarers. Int J Epidemiol 1996 Dec;25(6):1237-43.

[vi] CHIRP Maritime. https://www.chirpmaritime.org Accessed 9th June 2021.

[vii] Hansen HL, Nielsen D, Frydenberg M. Occupational accidents aboard merchant ships. Occup Environ Med 2002;59:85-91.

[viii] Jensen OC, Laursen FV, Sørensen FL. International surveillance of seafarers' health and working environment. A pilot study of the method. Preliminary report. Int Marit Health. 2001;52(1-4):59-67.

[ix] Jaremin B,.Kotulak E. Mortality in the Polish small-scale fishing industry. Occup Med (Lond.) 2004;54:258-60.

[x] Roberts SE, Jaremin B, Marlow PB. Human and fishing vessel losses in sea accidents in the UK fishing industry from 1948 to 2008. Int Marit Health. 2010;62(3):143-53.

, Aasjord HL. Tools for improving safety management in the Norwegian Fishing Fleet occupational accidents analysis period of 1998-2006. Int Marit Health. 2006;57(1-4):76-84.

[xi] Allen P, Wellens B, Smith A.  Fatigue in British fishermen. Int Marit Health. 2010;62(3):154-8.

[xii] Schnitzer P,.Russell J. Occupational injury deaths in Alaska's fishing industry, 1980 through 1988. Am J Public Health. 1993; 83: 5-8.

[xiii] Lincoln J, Husberg B, Conway G. Improving safety in the Alaskan commercial fishing industry. Int.J Circumpolar Health. 2001(a); 60: 705-13.

More Articles ...

  1. E.4 Chemical Substances
  2. E.5 Radiation
  3. E.6 Noise
  4. E.9 Ship building and repair