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Boyan Atanaschev
It is more effective, and usually cheaper, to reduce the emission of a contaminant at source, rather than to develop ways of removing the contaminant from the workplace, once it has been released and dispersed. Sources of exposure should be reduced in number, size, emission or release rate, as much as possible. It is often not possible to obtain adequate and reliable control unless this is done. Both the processes and procedures need to be considered. To identify how people get exposed during work activities, it is essential to recognise the principal sources and how the contaminant is transferred within the workplace. It is easy to miss significant sources and causes of exposure.
Processes and activities can lead to the emission and release of contaminants. The way they do this and the scale of emission and release needs to be understood. Once this assessment is available, alterations can be developed to minimise emissions, release and spread of contaminants. It is best to do this at the design stage, but it may well be possible to make useful and relatively low-cost changes to existing processes. Identify and control the worst sources first. In practice, improvements to production and quality can often be useful additional benefits from such re-examinations.
People working near a process may be significantly exposed even though those directly involved are protected, for example by wearing PPE. In these circumstances, the most practical option may be to segregate the process. It may be the only viable way to protect those people not directly involved in the process or activity.
Once the number and size of sources have been minimised, consider reducing emissions by enclosure or other means. Where enclosures are used, they should be big enough and robust enough to cope with the processes, and the energy of contaminant emission or release involved. For airborne contaminants, properly designed exhaust ventilation applied to the enclosure may be needed to minimise leakage into the workplace.
Design work methods and organisation to minimise exposure. This normally requires clearly defined and described work methods. Organise the work to minimise the number of people exposed and the duration, frequency and level of exposure. An example would be when painting or coating a large object. If containment is not feasible, then natural ventilation may, with the right precautions, be relied on to disperse vapour. This would be done best at the end of a shift, in controlled circumstances and when fewer people will be present.
In addition to identifying significant sources, it is essential to identify and consider all work groups that may be exposed. It is easy to miss or underestimate the exposure of those engaged in non-routine activities such as work done by maintenance personnel and contractors. Also, be aware of, and have contingency plans for dealing with, failures of control and emergencies. In many instances it is possible to predict those parts of a production process that are likely to fail suddenly and modify or maintain them appropriately. Control measures, at the outset, should be designed for ease of use and maintenance. If they include working methods that are difficult to follow or involve hardware that is difficult to repair, the control measures will probably not be maintained or sustained. Their effectiveness will fall inevitably, and exposure will rise.
The physical, chemical and infectious properties of a substance, in the circumstances of use, have a great bearing on which route of exposure, or combination of routes, is most important. If there is no exposure, there is no risk to health; but usage nearly always leads to some exposure. So, consider:
In some cases, it might be immediately obvious that not all routes apply. For example, for people exposed to crystalline silica, the only relevant route of entry is by inhalation. Whereas, for work at room temperature with a low volatility substance, such as dimethyl formamide, the primary route of entry will be through the skin. Therefore:
Where inhalation is the most relevant route, the main focus for control will be sources of emission to air. Where the main concern is ingestion or effects on, or as a result of penetration through the skin, then the main focus for control will be sources of contamination of surfaces or clothing and direct contamination of the skin.
Exposure assessments should identify and, if at all possible, grade or rank the contribution of all routes of exposure (inhalation, skin and ingestion) to total exposure. In this way control effort can be directed at the main sources and causes of exposure.
Prevent skin contact where possible if contamination may lead to skin absorption, ingestion or direct health effects on the skin. Regularly clean all surfaces that can become contaminated. The frequency of cleaning should be based on the rate at which the surfaces become contaminated and how often skin is likely to come into contact with them.
Gloves are often used to provide protection against skin contact with hazardous substances. However, transfer of contamination from the outside of protective gloves to the inside is common. Train users in the correct techniques for putting on and taking off their gloves. Ensure all surfaces, which need to be cleaned, are made of materials that are easily cleaned. For instance, use work surfaces, which are impermeable and smooth so that they are easy to wipe clean and easy to test by surface sampling, if necessary.
The more severe the potential health effect and the greater the likelihood of it occurring, the stricter the measures required to control exposure. Control measures that are adequate will take into account the nature and severity of the hazard and the magnitude, frequency and duration of exposure. They will be proportionate to the risk.
Consider the consequences of failure to control exposure adequately. If the health effects arising from exposure are less serious, such as simple, reversible irritation, and are not likely to cause long-term harm, it may be sufficient to reduce exposure by simple, low-cost measures such as replacing lids on vessels or cleaning work areas regularly. In such cases, it may be unnecessary to go to greater trouble and expense to reduce the risk even further. Where the health effects arising from exposure are more serious, such as cancer, asthma, allergic dermatitis, severe disease or other irreversible and disabling health effects, and there is not enough information to establish a no-effect level (remember that biological agents will not have a no-effect level), then exposure will need to be reduced to low levels. How low these levels need to be will depend on the nature of the hazard, the likelihood of harm occurring and the degree of confidence in the information on potential health effects. The control measures necessary, in this case, might be extensive, take time to develop and implement, and be relatively costly. The measures should control the risk of both long-term (chronic) and short-term (acute) health effects.
Where sufficient information about the health risks has not been made available, employers have a duty to find it. Information on the classification of biological agents can be found in Schedule 3 of the COSHH Regulations. In practice, suppliers, relevant trade association or specialist advisers, such as an occupational hygienist, should be able to guide employers towards the appropriate control measures for their particular circumstances. Even where there is little information on the toxic properties of the substance or material, it is possible to make decisions about control options based on the properties of similar substances or materials.
Some substances have exposure benchmarks, such as Workplace Exposure Limits (WELs) or other exposure standards. If these are well-founded, they can provide useful guidance in indicating how stringent control measures need to be. If people are potentially exposed to, say, 100 times the appropriate benchmark standard, then the performance of the control measures will need to be much greater than if the potential exposure was only twice the benchmark. This is the basis of the control approaches in COSHH essentials20 and may be useful for substances for which there are no exposure benchmarks. However, it is important to use exposure benchmarks critically. The user should know the basis of the benchmark, how well-founded it is and any residual risks at, and below, the benchmark exposure level. Well-founded means that the standard is based on a substantial amount of evidence which allows a coherent understanding of health effects, and how these relate to exposure. This, in turn, enables decisions to be made on how health protective a standard should be. The degree to which exposure should be reduced below this standard will depend on a number of factors. These include the severity of the harm being prevented, the likelihood that harm will occur and the degree of uncertainty associated with the standard.
Sometimes, control measures may be selected which reduce exposure more than is strictly necessary. Usually, this occurs because some controls are more convenient and acceptable. For instance, people may prefer to wear air-fed RPE rather than filtering devices, although the protection offered by the latter would be adequate, if well fitted. Such cases do not undermine the general principle that, overall, control measures should reduce exposure to a level which minimises any risk to health.
Control measures should be kept under review to ensure they remain effective enough in the light of new information. Knowledge and understanding of the potential health risks from substances may change. Advances in the process and control technology and work organisation may enable changes to be made to reduce exposure. Keep abreast of, and apply, industry good practice for the control of substances hazardous to health.
Some control options are inherently more reliable and effective than others. For example, the protection afforded by personal protective equipment (PPE) is dependent upon good fit and attention to detail. In contrast a very reliable form of control is changing the process so that less of the hazardous substance is emitted or released.
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