During a voyage cargo is usually isolated from working and living areas, although there may be occasions, such as entry into areas adjacent to cargo holds or the cleaning or inspection of empty cargo tanks or hold when exposure can occur. When loading or unloading cargo there is considerable scope for exposure.

Bulk oil and chemical transport

The largest volumes of hazardous substances are carried in bulk oil and chemical tankers. Crude oil carriers are usually large or very large vessels. The voyages are usually long from oil producer to refinery, and the loading and unloading operations are usually at intervals of weeks. Crude oil constitutes a complex mixture of hydrocarbons, and other substances such as sulphur compounds. Acute intoxications with volatile hydrocarbons or hydrogen sulphide have been described, especially during loading and tank cleaning operations. Hydrocarbons affect mainly the nervous system and may cause dizziness and nausea, or after high exposure, unconsciousness. Hydrogen sulphide has an unpleasant odour in low concentrations and is highly poisonous as it blocks certain enzymes in the mitochondria, which can lead to unconsciousness or death at high exposures. In moderate concentrations it can cause irritation of the mucous membranes. In order to reduce the risk of explosion on crude oil carriers, washed engine exhausts are often used as an inert gas to fill the remaining void in the tank instead of air. Engine exhaust can have a comparatively high concentration of nitric oxides, which are mucosal irritants and could cause asthma, but the major problem from inert gasses in the lack of oxygen (see Enclosed spaces below).

Product tankers are usually smaller coastal tankers, which carry gasoline, diesel, or other refined petroleum products, and sometimes intermediate products from refineries. The content of benzene used be up to 5 % in gasoline but is now much lower, and may be up to 100% in feedstocks for the chemical industry. Product tankers often load and unload their cargo on a daily basis.

Chemical tankers are constructed to carry a large number of chemicals, some of which could be hazardous and poisonous, including acrylonitrile and phenol, which are acutely toxic and isocyanates, which can cause asthma. The level of safety is usually higher on chemical tankers than on product tankers. There are stringent regimes in place for vetting the precautions and quality of management of such vessels in developed countries. Stringent cleaning procedures are required between loads and these may require the use of corrosives, such as caustic soda, within enclosed spaces.

Exposures to cargo vapours on tankers are usually highest during loading, unloading and tank cleaning operations, but deck crew can also be exposed during work at the manifolder or in the pump room. The first mate is usually responsible for the cargo and the operations on deck. The exposure to e.g. hydrocarbons used to be very high, especially during open loading (with the manholes or ullage holes open) when the concentrated cargo vapours are evacuated on deck. Manual gauging during top off (the last phase of the loading) used to be common on older tankers. The mate was often looking down through the manhole during the loading in order to be able to stop the loading when tank was full. The exposure at these occasions could be very high.

Some years ago ships were designed to use closed loading systems with automatic gauging of the cargo, but still the cargo gas has to be evacuated, usually through so called high jet vents. If there is no wind, the vapours could fall down on the deck, and also seek their way into the living quarters. More recently, and mainly because of environmental protection standards, fully closed loading and discharge systems have been introduced that return vapours from the ship’s tanks ashore where they are enclosed and re-processed.

Health effects of exposure to petroleum vapours (hydrocarbons)

Volatile hydrocarbons from petroleum products, such as gasoline, kerosene or white spirit, can affect the central nervous system. Acute effects include symptoms such as fatigue, headache, nausea, dizziness, and, in severe cases, loss of consciousness. Very high or prolonged exposure (at least 5-10 years) have been identified as a cause of cause neurobehavioural effects such as chronic toxic encephalopathy (CTE), with persistent symptoms such as asthenia, impaired memory, and concentration, and emotional disturbances. However, only few cases of CTE have been reported among seafarers.

Seafarers on coastal tankers have been shown to have an increased incidence of leukaemia, lymphoma, and multiple myeloma, possible due to exposure to benzene from gasoline, and other petroleum products.[1] It is well known that benzene may cause leukaemia, especially acute myeloid leukaemia (AML). High exposure, above 50 ppm (parts per million, averaged over the working day) causes leukopenia, and in rare cases aplastic anaemia. The occupational exposure limit (OEL) in most European countries is 0.5 ppm or 1.5 mg/m3 (8 h time-weighted average). The exact mechanism for the leukaemogenic effect is not known in detail, but several genotoxic substances are generated during the metabolism of benzene.

Personal sampling of benzene in air by e.g. dosimeters can detect hazardous exposure to benzene at an early stage. Benzene can also be detected in alveolar air, which reflects the benzene concentration in blood. This reflects exposure during the last hour or so. More practically analysis for benzene metabolites, such as trans, trans-muconic acid or phenyl mercapturic acid in urine can provide estimates of exposure over a timescale of hours. Phenol in urine can also be used as a biomarker for exposure during the last day, but if the exposure is high (above 20 ppm). Thus these methods are only valid if used to monitor risks from recent periods of exposure or after a spill. They are totally useless as screening methods when used at the start and finish of periods at sea.

 Increased levels of biomarkers for cytogenetic and other genotoxic effects have also been described in research projects, but are at present stage these are not suitable to use for surveillance of individual exposure since the effects linked to exposure are only seen on group levels, and the results could be affected by other factors. Routine collection and analysis of white blood cell counts on persons occupationally exposed to benzene is not very sensitive and is not recommended.

Prevention of health effects from exposure to cargo vapours on tankers

The best primary prevention is by technical measures, such as installation of closed systems. In certain situations effective personal protective equipment, such as facemasks, preferably with external air supply, could be used (see section on respiratory protection below). Information and education of the crews are also very important. Little monitoring to determine levels of exposure during cargo handling operations on modern ships has been undertaken. This is important both as a means of identifying activities where exposure occurs and for monitoring the integrity of the control measures that are in place. Routine tests of blood, urine, and respiratory function are of limited value, but interviews and questionnaires about exposure and symptoms may reveal hazards, which can then be prevented.

Other ships carrying dangerous cargoes

Intoxications of seamen on mixed cargo ships transporting chemicals in bulk or in barrels have been described. It is important that the seamen have good information about the content of the cargo and of its possible health effects (see material hazard data sheets below). They should be informed on the proper handling of the cargo, protective measures, and how accidental poisonings should be treated. Lung cancer and mesothelioma among seamen working on ships carrying asbestos has also been described but such asbestos is now rarely traded. Shipping containers are normally sealed prior to dispatch and only opened again when they have been offloaded ashore. These may contain significant levels of contaminants either because of off-gassing from the materials packed or from fumigants used to control pests or conform to requirements aimed to prevent dispersal of pests. Ship’s crew are not normally exposed and any risks are to those unpacking containers or to customs and port health staff checking the contents.

Oxygen-depleting substances

Regulations governing the transportation of solid bulk cargoes are published by the International Maritime Organization (IMO) in the International Maritime Solid Bulk Cargoes (IMSBC) Code.[2] Advice on their properties and methods of handling is given in the schedules for the individual cargoes. The IMSBC Code lists the following cargoes as potentially oxygen depleting; brown coal briquettes, charcoal, coal, copra, direct reduced iron (iron sponge), iron oxide, ferrous metal borings (shavings, turnings or cuttings), fish (in bulk), fish meal (fish scrap), metal sulphide concentrates, mineral concentrates, silico-manganese, tapioca, peat moss, seed cake, ammonium nitrate-based fertilizers, sawdust, wood pellets, wood products (logs, timber, saw logs, pulp wood, round wood), wood chips, limestone and linted cotton seed.

Inorganic materials deplete oxygen in air through chemical oxidation. Some oxidation products may be emitted as gases, e.g. carbon monoxide (CO) and carbon dioxide (CO2) and create an additional risk in addition to the oxygen depletion.  Organic materials are subject to decomposition over time, principally due to either microbiological or chemical oxidative processes. Various gaseous products are formed including CO, CO2, hydrogen sulphide (H2S) and hydrocarbons.

Whenever oxygen-depleting substances are transported or stored in an enclosed space special care must be taken before entering such space or any space communicating with it (see section on Enclosed spaces below).

When oxygen depleting cargoes or materials that emit toxic substances are stored in enclosed spaces, toxic levels may be reached rapidly. Toxic levels of CO, CO2 or oxygen depletion do not have any natural warning properties such as odour and are thus impossible to detect without measurements. Traditional breathing mask filters will not capture CO or deal with oxygen deficiency. The only feasible way to enter such toxic atmosphere is to wear an air fed or self-contained breathing apparatus (SCBA). Fumigated cargoes may also possess dangerous properties and toxic levels of gaseous fumigants may enter and accumulate in enclosed spaces above and adjacent to the stored material.

The cargo holds and communicating spaces in bulk carriers, particularly stairways leading to the cargo holds, are examples of enclosed spaces where toxic atmospheres may develop.

The limited time slots in ports for the discharge of cargo do not always allow for proper ventilation of enclosed spaces and several fatal accidents have occurred when people have entered unventilated stairways. In one study, CO levels close to 15.000 ppm and oxygen depletion as low as 0.8% O2, were reported in cargo holds and connecting stairways during shipment of wood pellets.[3]  Transport of logs and wood chips in enclosed spaces may result in rapid and severe oxygen depletion and CO2 formation.[4] Thus, these apparently harmless cargoes may create potentially life-threatening conditions in enclosed spaces. In Scandinavian ports and waters alone, a total of nine fatalities and several injuries were reported between 2005 and 2011. All victims had entered inadequately ventilated stairways, communicating with cargo holds. In several cases two persons died, the second would-be rescuer, probably acting on instinct and emotion rather than knowledge and training and thinking the first person merely had suffered a fall.

Health hazards on car decks

Crew working on car decks of ferries and car transporters are exposed to engine exhaust.[5] For diesel engines, the main exposures are to nitric oxides, which can cause respiratory effects, and to fine soot particles, which contain will contain carcinogenic polycyclic aromatic hydrocarbons among their components. Gasoline engine exhaust contains carbon monoxide, which can cause headache. Pollution is increased when engines are started from cold. A requirement not to start engines prior to disembarkation and good ventilation of the car deck are both important.