Principles of good control practice

Design and operate processes and activities to minimise emission, release and spread of substances hazardous to health

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.

LEV is an important option for controlling exposure. LEV systems consist of an airmover (usually a fan), an aircleaner, ductwork, and inlet hoods or terminals. Many designers and much ventilation guidance concentrates on the airmover, aircleaner and ductwork. There is a strong tendency to treat the hood design as a minor matter often left to people onsite. Yet, if the airborne contaminant is not drawn into, or contained within, the LEV hood, exposure is likely to be poorly controlled. The hood size, shape, layout and airflow requirements should all be considered. This will define the design and airflow requirements for the other elements of the system (ductwork, fans, aircleaners etc). The hood should be designed to work effectively and cope with the way the process emits airborne contaminants. So, for instance, if the source is large or emits contaminant-laden air at high velocity, a small ‹captor' type hood will not be effective. Apart from considering the process to be controlled, the LEV should be designed so that it is easy to use correctly. LEV hood design should be compatible with the system of work and the operator's requirements, such as lighting and heating. LEV hoods and the working methods required to get the best performance from them should be designed using ergonomic principles

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.

Take into account all relevant routes of exposure – inhalation, skin and ingestion – when developing control measures

Exposure can occur through:

• inhalation;
• skin; or
• ingestion.

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:

•  the health effects that the substances can cause;
• the way the substances are used;
•  the degree of exposure; and
• how exposure occurs.

An adequate risk assessment considers all routes by which the substance might enter the body and, in the case of direct contact, how a substance might affect the skin.

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:

• identify all sources and routes of exposure; and
• rank these routes in order of importance.

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.

If the workroom is likely to become contaminated, and this contamination may contribute significantly to exposure, people should not increase their exposure by activities such as:

• eating;
• drinking;
• smoking; or
• using cosmetics

in the workplace. If the workroom is liable to be contaminated make sure people have clean areas to rest, eat and drink.

Where skin contact is relevant, provide:

• adequate and accessible welfare facilities for washing and changing;
• laundered or disposable work-wear. The frequency of laundering will depend on the degree of contamination and the hazardous nature of the substance;
• separate storage for day-wear and work-wear;
• clean facilities;
• segregation of clean and dirty areas if the risk of contamination is severe.

It is good practice to keep workplaces clean: cleaning methods should not lead to spread of contamination. Define what 'clean' means in your particular workplace and check against this standard.

Where dust exposure from contaminated work clothing could be significant, use clothing made from a low dust-retention and low dust-release fabric.

Control exposure by measures that are proportionate to the health risk

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.

Choose the most effective and reliable control options that minimise the escape and spread 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.

Choose the most effective and reliable control options for the circumstances and direct these at the main sources and causes of exposure. There is much good advice on the engineering control aspects of control measures and the application of ergonomic principles (see References and further reading).

There is a broad hierarchy of control options available, based on inherent reliability and likely effectiveness. COSHH regulation 7 refers to many of these options. They include:

• elimination of the hazardous substance;
• modification of the substance, process and/or workplace;
• applying controls to the process, such as enclosures and LEV;
• ways of working which minimise exposure; and
• equipment or devices worn by exposed individuals.

The key message is that there is a hierarchy of reliability of control options and this is often linked to their effectiveness.

Eliminating the substance means there cannot be any exposure. Always consider elimination first. If this is not possible, a reliable form of control is to change the process so that it releases less substance. Controls applied to the process might be as effective, but will require maintenance and are unlikely to be as reliable.

For example, the effectiveness of an LEV hood, used to contain and remove contaminant-laden air, requires that:

•  the system supplying the suction to the hood is maintained regularly; and
•  the person using the hood works in a specific way to get the best performance out of it.

These, and other factors, mean that LEV will not usually provide protection which is as reliable as changing the process. Even though both control methods might, in theory, be equally effective.

Achieving a reliable, defined, sustained reduction in exposure using respiratory protection can be even more difficult and offers no protection to others working nearby not wearing respiratory protection.

Giving people PPE such as gloves or respirators may appear to be the quick, cheap and easy option. In practice, it is likely to be the least reliable and effective option. It may not actually be the cheapest if a PPE programme is compared like-for-like with the cost of providing other control options.

Develop a set of integrated control measures that are effective and reliable enough to control exposure adequately. Take care not to see the 'hierarchy' of reliability and effectiveness so rigidly that some control options are viewed as automatically 'good', while others are seen as 'bad'. This good-bad view can get in the way of developing what is needed – effective, reliable, practicable and workable control measures.

There is a large range of control options available. Each will have its own characteristics as to when it can be applied, how much it can reduce exposure, and how reliable it is likely to be. As a matter of principle, the aim should be to select from the most reliable control options. Again, it is important not to be too fixed in one's thinking as, in many cases, an effective set of control measures will turn out to be a mix of options – some more reliable than others.

Whoever designs control measures needs appropriate knowledge, skills and experience. The competencies needed will depend on the scope and complexity of the exposure problems to be addressed and solved. If a set of control measures is already in place, but the LEV system is not performing well, then the solution may be purely a matter of ventilation engineering. But, if controls are minimal or inadequate, and it is not clear how overexposure is occurring, analysis of exposure and development of effective control measures will be necessary. This may require the competencies, skills and knowledge of a professional occupational hygienist. He or she should be able to specify the hood design of any LEV system (if one is needed), but may well require the services of a ventilation engineer to design, fabricate and install the system. Or it may be that changing the process is an option, in which case the skills and knowledge of a process engineer may be required. The individual or team involved need the right mix of knowledge, skills and experience.

Where adequate control of exposure cannot be achieved by other means, provide, in combination with other control measures, suitable personal protective equipment

Effective control measures usually consist of a mixture of process and/or workplace modifications, applied controls (such as local exhaust ventilation) and methods of working that minimise exposure and make the best use of controls. Sometimes the mix includes PPE, such as respirators, workwear or gloves.

PPE tends to be less effective and reliable than other control options, because it:

• has to be selected for the individual;
• has to fit the individual and not interfere with their work or other PPE worn at the same time;
• has to be put on correctly every time it is worn;
• has to remain properly fitted all the time the individual is exposed;
• has to be properly stored, checked and maintained;
• tends to be delicate and relatively easily damaged; and
• fails to danger, sometimes without warning.

The possibility of failure at each of the steps needed for successful use of PPE makes it difficult to achieve sustained and effective exposure control across a population of people. Even if a reliable, defined, sustained reduction in exposure is achieved using PPE, it offers no protection to others working nearby not wearing PPE.

Control options, such as change of process or applied controls, are likely to be more effective and reliable than PPE. They will probably be cheaper long term, but it may take longer to plan and organise them. It is important not to rely solely on PPE as the only control option and believe exposure is adequately, effectively and reliably controlled. Unless, that is, PPE really is the only feasible control option. Normally, PPE should be used to secure adequate control in addition to the application of process, operational or engineering measures, and where adequate control of exposure cannot be achieved straight away, or solely by application or use of these other measures.

Where PPE is an essential element in a set of control measures, a programme to organise and manage this element will be required. PPE, including RPE, requires proper:

• selection;
• fitting;
• use;
• storage;
• checking and maintenance; and
• training.

A PPE programme involves the careful, routine and trained behaviour of people, including wearers and supervisors. If used, it must be set up carefully, managed properly and checked regularly.

PPE should be both adequate and suitable. Adequate, in this context, means technically capable of providing the required degree of protection; appropriate selection will be very important. Suitable means correctly matched to the needs of the wearer, the job and the work environment. Choice, comfort, user trials and supervision will all be important.

Sometimes the PPE chosen may offer protection that is more than adequate, but is chosen for its suitability. For instance, an airline hood may be more comfortable and, therefore, more acceptable than a full-face mask, even though the additional protection is not indicated from the risk assessment.

As with gloves, shoes and clothing, one size of respirator will not fit everyone. People must be offered a choice of device. This is especially the case for half-mask devices which need a good and complete fit against the face of the wearer to work effectively. Check the fit of RPE using the proper test method.

Train users and supervisors in the use, storage, checking and maintenance of PPE, including RPE.

Check and review regularly all elements of control measures for their continuing effectiveness

Once an effective set of workable control measures have been devised, they need to be put in place and managed. This includes training all relevant people in the use and maintenance of the control measures. The requirement for maintenance covers all elements of the measures to get effective and sustained control of exposure. These include any defined methods of working, supervisory actions, record keeping etc (ie the 'software' of control) as well as the 'hardware' of control. Certainly whatever hardware is involved must be checked and must continue to function as intended. But a similar approach needs to be taken to check the actions people must take and the methods of working they need to adopt. These need checking and correcting, if necessary, too.

The effectiveness of control measures should be checked regularly. Which checks, and how often, will depend on the particular control measures and the consequences if the measures fail or degrade significantly. Process changes are likely to be more stable and reliable than, say, LEV. In turn, LEV is likely to be more stable and reliable than controls that rely on routine human behaviour. In practice, it is necessary to draw up a simple practical programme for checking essential elements in each set of control measures. For instance, it may be necessary to check every week that people are still adopting the correct methods of working. Checking on the working of the LEV may only be needed every month. Checking the continuing effectiveness of the process changes may only be needed every six months. But it is important not to miss the basic checks. It may be very obvious that an important element of a set of control measures, for instance LEV, has failed and the operator may well be in the best position to check this.

Initially, checks may be needed quite frequently. After this baseline period, the records should show the pattern of deterioration or sustained effectiveness. The frequency of checks can then be adjusted to what is needed to keep the control measures effective. There is nothing more likely to cause people to ignore or not take checks seriously than routinely measuring and recording 'no change' over long periods of time. Checks have to have some purpose and meaning.

Exactly what checks should be done will depend on:

• the control measures in use;
• how reliably they control exposure;
• how well characterised they are; and
• the consequences of control degradation or failure.

When control measures are known to be reliable and effective, the focus of attention should be on checking the critical elements of the measures to ensure continued effectiveness. Where reliability and effectiveness are not known, it may be necessary to assess or measure exposure to hazardous substances. It may be that an experienced person, competent in occupational hygiene assessment techniques, can make such assessments using skill, knowledge of the processes and simple tests. But it may also be necessary to measure exposure in a direct way, by air sampling or biological monitoring and comparing it with any WEL or similar exposure benchmark. Other quantitative tests might be needed, such as surface wipe measurements to measure the spread and accumulation of contamination.

Inform and train all employees on the hazards and risks from substances with which they work, and the use of control measures developed to minimise the risks

For control measures to be effective, people need to know how to use them properly. Most importantly, people need to know why they should be bothered to work in a certain way and use the controls as specified; they need to be motivated.

Motivation comes from understanding what the health risks are and, therefore, why the control measures are important. It is also comes from the user having confidence in the control measures and believing that they will protect his or her health. If the health risk is serious, for example silicosis or cancer or asthma or allergic dermatitis or blood-borne disease such as HIV, and is chronic or latent in nature, a good appreciation of the risk is especially important. With latent or delayed risks, exposure can often be excessive, with no short-term warning, such as smell or irritation, to indicate that anything is amiss. The people potentially exposed need to be told, clearly and honestly, why they should use the control measures, and the consequences in terms of ill health, if they don't use them.

People need to know how control measures work to use them correctly, and to recognise when they are not working properly. This means training operators directly involved, and also supervisors and managers. This is so that everyone can identify when controls are being used in ways that reduce their effectiveness. It is important to know whether the individual is working in a way that reduces the effectiveness of control measures because:

• there is no other way of doing the job; or
• because he or she does not know any better.

If the control measures are difficult to use or get in the way of doing the job, they will need redesigning. If the control measures are well designed and tested but are still misused, then the individual needs retraining and motivating.

Most control measures involve methods of working which means that, at the design stage, it is essential to ask workers and supervisors for their views on how best to do the work, so exposure is minimised. They should be asked whether a proposed method of working is practical and how to get the best out of the proposed control measures. People who are actively involved in the development of control measures are more likely to 'own' them and respond positively to new ways of working that may be required. Easily followed, convenient and simple procedures, which minimise exposure, and are built-in to the working method, are more likely to be followed.

Ensure that the introduction of measures to control exposure does not increase the overall risk to health and safety

Process changes, enclosures, ventilation, new methods of working, PPE and other changes to control exposure can introduce new risks. For instance, process changes might mean that equipment cannot be fully decontaminated before maintenance staff are given repairs to do. Enclosures might create an explosion risk if they could contain potentially explosible aerosols. New methods of working may create risks of musculoskeletal injury. LEV has to be maintained, introducing possible risks of access and manual handling of heavy parts. PPE can restrict movement, feel and vision. And some controls may increase environmental emissions.

People designing control measures should look for these 'new' risks and minimise them. They must not only focus on the risk from substances hazardous to health. A good control solution is one which minimises the health risk, while reducing maintenance burdens, being relatively fool-proof, and not introducing other risks (see regulation 3 of the Management Regulations).