Industrial Hygiene is the discipline of anticipating, recognising, evaluating & controlling health hazards in the working environment with the objective of protecting worker health.
It includes the development of corrective measures in order to control health hazards by either reducing or eliminating the exposure.
The four key elements of industrial hygiene are:
Anticipation starts at the design stage of any new project, for instance during ship design, and includes a review of requirements for safe operation and for modifications to specifications to achieve this, new processes, emerging health risks (new research/findings) and new circumstances (new legislation/legal requirements). Often there are well developed points of reference in other industrial sectors, thus the known risks in the chemical industry will be important in the design of ships for chemical transport.
There are industrial hygiene hazards inherent to the Shipping industry. Some may arise from the operation of the ship itself, some during maintenance and others relate to the cargo carried. It is important that these hazards are recognised - common hazards by category are listed below;
TYPES OF HAZARD
- Vapours - (hydrocarbons, paints & thinners, solvents, mercury).
- Gases - (hydrogen sulphide, mercaptans).
- Dust/Fibres - (refractory ceramic fibre, asbestos).
- Fumes - (welding fume – these can contain nickel, cadmium, zinc, chromium )
- Mists/Aerosols - (cargo tank degreasing agents).
- Liquids - (mercury, paints, boiler room chemicals etc.)
- Corrosives, irritants and allergens as vapours, gases or liquids – acids and alkalis, solvents, detergents.
- Noise - (unwanted or excessive sound).
- Vibration - (hand-arm and whole body).
- Radiation - (Non-Ionizing such as UV, ionizing - including naturally occurring radioactive material (NORM)).
- Monotony - (repeated motion).
- Work Pressure - (worry/fatigue).
- Overload - (perceptual/mental).
- Body Positions - (lifting/twisting/straining).
- Metabolic Cycles - (overtime/watchkeeping).
- Psychosocial - (relationships/feelings).
- Micro-organisms – (viruses/fungi/bacteria)
- E.g. Legionella bacteria
A harmful agent has to gain access to the body to cause adverse effects. The routes of entry and location of the harm will depend on the agent. Chemicals, other substances and microorganisms commonly enter by inhalation or skin contact, but sometimes by other routes such as ingestion or injection.
Noise has it major adverse effects on the ear as the sensitive sound receptor organ, vibration can either have local effects on the hands or more generally depending on its frequency and the part most exposed. Non-ionising and ionising radiation may either effect the locations where they deposit energy in the body or may have more general consequences.
Ergonomic risks may be manifest as musculo-skeletal problems or, where there are psychosocial aspects to them, as changes to cognition, mood or attitudes.
TYPES OF EFFECTS
The effects of exposure to harmful agents can range from minor irritation or discomfort to serious organ damage or even death.
Acute and delayed effects
The negative health effect of exposure can give immediate and serious health effects and the incident will then be classified as an accident. These are known as short-term or acute health effects. Most often exposure will not result in any acute symptoms but nevertheless it may cause the development of a disease that will not show any symptoms for many years. Sometimes the disease will not be recognised until after retirement and the relation to work may not be thought of. These are known as long-term or chronic health effects. Ship design and construction can be used to minimize the health risks of shipping.
Single exposure and total dose over a long period
Health effects may develop after a single exposure but most often will be the consequence of repeated exposures over a long time period. A typical example will be the time lag between significant exposure to benzene and leukaemia.
Specific and non-specific relations between exposure and effect
Some specific exposures can lead to specific health effects and some will lead to signs and symptoms that are similar to those arising from other causes, such as asthma and dermatitis. Specific effects are easier to discover, to diagnose and to prevent through risk assessment and risk management than non-specific ones.
Individual predisposing factors
There are individual differences in how prone each individual is to develop negative health effects caused by work related harmful exposure. Differences may be by inherited as the tendency to develop allergy. Other differences may be caused by “self-exposure” like smoking.
Synergetic effects of multi-exposure
There are known synergies between different exposures. A well-known synergy is the dangerous synergy between smoking and exposure to asbestos.
Evaluation is the process that assesses the hazards to workers from exposure to harmful substances or conditions.
Evaluation of the risk should be based on the following information;
- Toxicity/Hazard - The substances used and produced (chemical, biological) plus other agents (noise, radiation) and factors (ergonomic) present. The Material Safety Data Sheet should be reviewed for chemical hazards.
- Form of Hazard - The form of the substances (gas, vapour etc.) and other agents plus a knowledge of where these are present in the workplace location/task undergoing assessment.
- Level of exposure (the amount/concentration of agent/substance, the frequency and duration of exposure).
- Occupational Exposure Limit (if available) - The level below which there is not expected to be any adverse effect on health for the majority of the working population.
- Health Effects - An understanding of the effect(s) of the relevant agents/factors (chemical, physical, biological, ergonomic) on the body.
- Process/Operational Understanding – The nature of the process or operation and awareness of operations that may result in the release of chemicals or energy that could cause harm
- Work/shift - shift durations and patterns.
- Maintenance Activities – (knowledge of infrequent events, leaks and releases).
- Interview – (information provided by workers)
- Control Measures - Any control measures that are already in place
- Industrial Hygiene reports - Comparing current results to previous results is a way of determining the effectiveness of new or modified control measures.
The relationship between dose and the probability of effect is important. In many cases it is difficult to find valid data. Data are often derived from experimental animals and are extrapolated to humans. Doses in experiments are often high and data are extrapolated to lower doses. A no effect exposure level can also be established through a consensus process. To compensate for the extrapolations a safety factor is included in the estimate of the "safe" dose. This is typically a factor of 10 for each unknown step.
Toxicology, epidemiology etc.
Data from toxicology, epidemiology, psychology and other sciences are of great value in the processes of health risk evaluation. Quantification of exposure is needed to perform a valid risk assessment. It may be necessary to assess the estimated level of exposure until monitoring is undertaken to quantify the level of exposure.
Monitoring means the use of valid industrial hygiene techniques to derive a quantitative estimate of the exposure of employees to substances hazardous to health. The monitoring process should also include observation; awareness of the presence of potential health hazards as processes undergo change; assessment of the control measures in place.
Monitoring is carried out in two ways:
Personal monitoring is the measurement of an individual worker’s exposure to hazardous substances in air, or to agents such as noise or vibration. Results of personal monitoring, expressed as a time-weighted average are directly comparable with Occupational Exposure Limits.
Area / static / spot monitoring can also offer limited information on an individual’s exposure. It is more useful in providing a guide to the sources of contaminants, effectiveness of control measures and the general work areas atmospheric concentrations.
Noise meters, Drager tubes, CMS (Chip Measurement System)analyser, mercury meter are all examples of area / static monitors that are used in the shipping industry for area monitoring. Area monitoring should always be conducted in a methodical manner, using a properly calibrated meter. The results of meter readings are only as good as the meter’s last calibration. Meters need to be calibrated on a regular basis, following the manufacturer’s instructions.
Always check that the meter is functioning properly. On start-up, most meters will run through a self-test.
The ultimate objective of industrial hygiene is to eliminate or minimize risk to health by preventing, or controlling, exposure.
The best way to achieve control is by addressing the source of the hazard. In most cases effective control strategies will utilise combinations of several, if not all of the measures listed.
The ‘Hierarchy of Control’ with regards to industrial hygiene is as follows:
- Engineering Controls
- Personal Protective Equipment (PPE)
The most effective form of prevention control is simply to either eliminate the use of the hazardous agent, the process in which it is used, or eliminate hazardous equipment e.g. high noise/vibration. This is not often a practical option.
Substitution of a substance, with either an alternative product or a different form of the same substance, is often a more practicable means of preventing exposure.
Wherever possible, hazardous substances, processes or equipment, which involves risk to health, should be completely enclosed. The person should have no contact with the health hazard. E.g. cargo contained in cargo tank; engine room chemicals contained in dosing systems.
Engineering controls involve process design and modification to control exposure e.g. Containment, enclosures, barriers, shields, noise insulation, ventilation systems.
Processes capable of producing exposures to hazardous substances only, are commonly controlled by the provision of mechanical air handling methods, of either one of the two types below or a combination of both.
Local Exhaust Ventilation (LEV)
LEV a mechanical air handling technique whereby potential airborne contaminants are captured near to the source of emission, extracted, and either discharged to a safe area, or air is cleaned and returned to the workplace. It is particularly valuable for situations that involve a point source release of toxic contaminants. An example of a LEV system on-board is in the fabrication workshop. LEV is often used at dry docks in tasks that use hazardous substances inside confined spaces e.g. welding, spray painting inside cargo tanks. Important considerations in the design/set up of LEV are;
- Size, shape and position of the source
- Physical nature of the contaminant
- Speed and direction of the source
- Rate of generation of the contaminant
- Nature of the operation
- Positions and movements of equipment and personnel
- Local air movements
General / Dilution Ventilation
Dilution ventilation is widely used on-board for the ventilation workspaces such as control rooms, mess rooms, workshops and laboratories. It is not normally suitable for the control of dust, mist of fume or for substances of moderate to high toxicity, or in situations where the rate of generation of contamination is non-uniform or high. General/dilution ventilation is used to:
- Maintain oxygen levels by provision of “fresh” air
- Reduce CO2 build-up due to expiration or “hot” work in confined space
- Dilute and remove trace contaminants, such as CO, NO, ozone etc.
- Remove (or add) heat, to maintain acceptable temperature
- Assist in controlling humidity
- Prevent formation of “stagnant air” regions, where localised oxygen depletion or high CO2, CO, NOx etc. concentrations can occur
LEV is used in combination where high hazard contaminants such as welding fume or spray paints are being used.
Hazardous processes / equipment can be segregated from lower risk ones by putting away from areas where lots of people working e.g. far end of workshop, separate room.
Administrative controls relate to how the interaction between personnel and the process/operation are organised.
Procedures document the steps to follow to minimise workers exposure including scheduling, good work practices and training to be in place.
Good housekeeping is particularly important where hazardous materials are handled. Clear labelling and appropriate storage are key controls.
Proper preventative maintenance schedules and regular inspection/leak detection of process plant; plus frequent maintenance, examination and testing of engineering controls are important administrative elements.
Other administrative controls include job/worker rotation and work/rest regimes.
Personal Protective Equipment (PPE)
PPE is normally considered to be the last line of defence and only applicable when other measures are insufficient or not practicable in achieving control.
Careful consideration must be given to the choice of the PPE. It is important that the protection is effective and comfortable. Regular maintenance is vital for many types of PPE if effective protection is be obtained