Rethinking the limits

The HSC is proposing major changes to the system for controlling workplace exposure to airborne chemicals, reports Chris Dyer.

British standards for the concentration of harmful airborne substances in the workplace were established for a few substances, such as cotton dust and asbestos, back in the 1930s. But the systematic setting of occupational exposure limits (OELs) was pioneered by the American Conference of Governmental Industrial Hygienists (ACGIH), which published the first list of OELs in 1948. The ACGIH intended that its list should be used in the practice of industrial hygiene as guidelines or recommendations in the control of potential workplace health hazards.

Britain, in common with many industrialised countries, adopted this list, and it was updated and published annually here from 1969 until 1980. In 1979, the HSC introduced control limits for several substances, and established its own system for setting OELs. This system has been adapted and in use ever since. The current system, which uses Occupational Exposure Standards (OESs) and Maximum Exposure Limits (MELs) has been in place since the Control of Substances Hazardous to Health Regulations (COSHH) were introduced in 1989. In essence, an OES is set for substances when it is possible to identify, with reasonable certainty, a level of exposure that is judged to pose no significant risk to health and that it is reasonably practicable for industry to comply with. Where such a level cannot be identified and the chemical has serious health implications for workers, an MEL is considered (see box 1).

System failures

Experience has revealed several flaws in the current system.

  • The concept of an OES being a "safe" limit offering complete health protection for all individuals is no longer tenable. "Safe" in this context is generally taken to mean the government has all the information needed to show that no harm will occur. But for most chemicals there are gaps in scientific knowledge on potential health effects and there is also a general lack of information on the ways that different individuals may respond.

  • The lack of a requirement in OESs to reduce exposure to as low as is reasonably practicable is out of step with current thinking. There are no fine lines between safe and dangerous concentrations of chemicals; and other major limit-setting bodies, such as the EC exposure limit setting committee, recommend exposure be reduced as far below OELs as is reasonably practicable in order to provide the greatest degree of health protection.

  • The indicative criteria for setting OELs are not comprehensive; some substances do not adequately meet the criteria for either an OES or an MEL. An OES can only be set where a level can be judged to be of no concern to human health and compliance by industry is reasonably practicable. Where this is not possible, an MEL is considered. But for an MEL to be set, the substance must have serious health implications for workers. For some chemicals, there is enough information to raise concerns that prevent a "safe" level being set, but not enough to establish that there are serious health implications for workers (see example in box 2).

  • The limit-setting process is resource intensive. The resources required in preparing the documentation and considering a limit proposal restrict the HSC to setting only 10-20 limits a year. There are around 100,000 substances registered in the EC market, of which 30,000 are marketed in volumes of more than one tonne. The HSC currently has limits for just over 500. By cooperating with other countries with the expertise to set OELs, such as the Netherlands and Germany, the HSC/E could reduce its resource commitment, but this commitment would still be considerable.

  • In the past 10 years, the EC has established its own system for setting OELs. Based solely on current scientific evidence, an expert committee recommends OELs in one of two categories: where the total scientific data leads to the conclusion that, below a clear threshold dose, exposure to the substance in question is not likely to lead to adverse health effects, the committee will recommend an Indicative Occupational Exposure Limit Value (IOELV), which is a health-based limit. Where for some adverse effects, such as genetoxicity and carcinogenicity, it is not possible, on present knowledge, to define a threshold of activity so that any level of exposure is a risk, the committee will recommend a Binding Occupational Exposure Limit Value (BOELV). Substances assigned IOELVs and BOELVs are eventually listed in EC Directives and member states are required to set limit values taking account of the EU limits. When the first IOELV Directive was implemented in 2001, many of the IOELVs proposed met the criteria for an OES. But for a few, this was not the case and as a consequence an MEL was set for these substances. More IOELV Directives are scheduled and there is a need to develop a limit system under the COSHH regime that will readily incorporate IOELVs. Otherwise the HSC's expert committees will have to spend time reviewing data that has already been considered at EU level, which is not a sensible use of resources.

  • There is a lack of understanding and awareness amongst employers, particularly in small firms, of OELs and how to comply with them. OELs were originally designed as a tool to help professional occupational hygienists in deciding what controls were needed and then in monitoring their effectiveness. With the introduction of COSHH, there was an attempt to move OELs from tools for health and safety professionals to limits that all chemical users have to understand and apply. Research by the HSE shows this transition has been unsuccessful. Although it found that the majority of chemical users were taking steps to control their employees' exposure, their knowledge of COSHH and OELs was very limited.

    Options for change

    In the light of these difficulties, the HSC does not consider that maintaining the status quo is an option, and it is now proposing major changes to the way OELs are set and maintained.1

    The first option involves minor modifications to the indicative criteria for OESs and MELs. This would solve the problem of substances that do not satisfy the criteria for either an OES or an MEL, and would make the system compatible with the system established by the EC:

  • MELs would be used as a default, so that all substances that do not meet the OES criteria automatically default to an MEL, irrespective of the extent of health concerns; and

  • an additional criterion would be added to the effect that an IOELV proposal is adopted as an OES.

    This option has the advantage of maintaining the familiar system, but it does not address the difficulties that small firms have in understanding and applying OESs and MELs. It would also lead to increasing inconsistency in the OES and MEL lists. For example, some substances with less serious or uncertain health concerns would get an MEL, with the attendant requirement to reduce exposure as low as reasonably practicable.

    Limits supported by good practice

    The majority of small firms are unaware of OELs; those that are aware have little idea how to determine whether they are complying with the limit. Even if the HSE managed to promote greater awareness, this would not automatically improve control as most firms do not have the specialist advice needed to measure exposure, compare data with OELs and decide whether changes are needed.

    The HSC's second option would overcome these problems by linking OELs explicitly to advice on good practice, the aim being that firms that apply good practice would comply with the OEL. This has the advantage that it does not impose new demands on employers and reduces the need for monitoring, while making it easier for employers to protect their employees. Good practice advice would also set OELs into the context of the other COSHH requirements and emphasise that control is not just about using engineering means to reduce exposure, but that process design, housekeeping and maintenance are all important considerations.

    As many employers are unaware of the difference between an OES and an MEL, and many that recognise the difference treat both limits as the same when deciding on control measures, the HSC believes there is an argument for moving to a single limit.

    "Adequate control" under the COSHH Regulations would be redefined as "apply the principles of good occupational health/hygiene practice; and comply with the limit value." Compliance with good practice would be the primary duty under COSHH with the limit as a "backstop". The good practice requirement would represent what a good employer currently does to ensure that an exposure limit is not exceeded. Good practice would reflect the nature of the hazard posed by the chemical, so that good practice for a mild nasal irritant would be different from that for a substance causing occupational asthma. Detailed good practice advice would set out how the principles of good hygiene practice set out in reg. 7 of COSHH are applied to specific task/substance combinations.

    This change would inevitably lose the "flag" that MEL substances are "nastier". This could be overcome by using a short phrase indicating the key relevant health concern, such as: "Breathing the dust can cause lung damage."

    Dealing with carcinogens

    To meet the requirements of the carcinogens Directive and the principles of good occupational health practice for carcinogens listed in the Directive and Schedule 1 of COSHH, practical control advice for these substances would reflect the need for stringent control and for employers to seek ways to further reduce exposure.

    An alternative way of dealing with the regulatory requirement to apply a higher degree of control to carcinogens would be to develop a two-tier system with a separate list for carcinogens. This would be a more visible way of distinguishing these substances from other chemicals. This would not perpetuate the current system, with one limit being regarded as "safe" and the other for "nastier" chemicals. The good practice advice for carcinogens would reflect the range of controls described in the HSC's carcinogens Approved Code of Practice, although for many substances, substance- or process-specific advice would also be needed.

    Criteria for setting OELs

    Limits supported by good practice would need new criteria for their establishment. These need to be flexible and provide as high a degree of health protection as possible, but also need to reflect the gaps in scientific knowledge, and differences in individual susceptibility.

    The HSC's current thinking is that it is not possible to set a single limit that represents an absolute guarantee of complete health protection for all individuals, as there will almost always be a degree of uncertainty. An OEL must also be legally enforceable and reasonably practicable with good standards of occupational hygiene practice. Taking account of these considerations and constraints, the HSC proposes two new OEL-setting criteria:

  • wherever possible, the OEL value would be set at a level at which no significant effects on human health would be predicted to occur based on the evidence available. If such a level cannot be identified with reasonable confidence or if it is judged that this level would not be reasonably achievable, then,

  • the OEL value would be based at a level corresponding to what is considered to represent good control, taking into account the severity of the likely health hazards and the costs and efficacy of control solutions. Wherever possible, the OEL would not be set at a level at which there is positive evidence of adverse effects on human health.

    Although there are two criteria for setting limits, the user would only encounter a single type of limit value for all substances and would have to comply in the same way. Limits would be set as eight-hour time-weighted averages (TWAs), with an additional short limit, a 15 minute reference period, being set as necessary.

    All of the options will reduce the drain on the HSC/E's resources because it will no longer be necessary to review the IOELVs or BOELVs listed in future EC Directives. These can be incorporated into the system through an administrative process. The simplified criteria associated with the good practice options would make it possible to streamline the current process, saving resources and eliminating the lengthy debates that sometimes occur on which type of limit is most appropriate for a particular substance.

    Giving good advice

    The HSC proposes providing advice to support the good practice limit options through an extension of the COSHH essentials system.2 Feedback since COSHH essentials was first printed in 1999 has been very positive. A large majority of purchasers of the guidance find it easy to use and 60% have used it to improve their workplace control of chemicals. The HSC is suggesting using the COSHH essentials good practice advice as a default for substances that currently have OESs in the range 0.001 - 10 microgrammes per cubic metre (mg/m3) and 0.05 - 500 parts per million (ppm).

    COSHH essentials uses generic risk assessments for hazardous supplied chemicals, based on checklists that guide the user through five simple steps. At the end of the process, specific advice on the control of the chemical used in a particular task is arrived at (see box 3). The basis of the system is a series of hazard bands based on the standard risk phrases used on the Approved Supply List and on material safety data sheets. But during its development the hazard bands were evaluated against target airborne exposure values. For example, the target airborne concentration range for hazard group A is >1-10 mg/m3 for dust and >50-500 ppm for vapour. The range of airborne concentrations covered by the COSHH essentials hazard bands A to D is >0.001-10 mg/m3 for dust and >0.05-500 ppm for vapour. This provides a link between the numerical values of OELs and the COSHH essentials hazard bands and control advice.

    MEL-type substances, such as those that cause asthma and genotoxic carcinogens, are assigned under COSHH essentials to hazard band E - "seek specialist advice". These substances would have to be assessed individually to see if the numerical value of their exposure limit would lead to a COSHH essentials control approach consistent with current good practice. If current good practice involves a different degree of control, then a substance-specific good practice advice sheet will be drafted and integrated into the system.

    The COSHH essentials approach does not work well for process-generated dusts and vapours (because factors used in the assessment, such as "scale of use", are not applicable). The HSC proposes to break the extensive existing industrial sector guidance down into specific activities, and draft COSHH essentials-style guidance sheets for each of the main unit activities within that industry.

    Making it available

    An important element in the HSC's proposals is making information on exposure limits, currently available as priced publications (EH40 and EH64), freely available on the internet.3 An electronic version of COSHH essentials was launched at the end of April.4 The advantages of this approach are that:

  • users can access and print out only as much information as they need;

  • information is available immediately 24 hours a day;

  • information can be combined from a variety of sources, such as EH40 and EH64, with links to other publications such as COSHH essentials; and

  • the information can be made available free of charge to anyone with internet access.

    Assessing the options

    The HSC has assessed the proposed options against seven objectives and their potential contribution to the Revitalising health and safety strategy (HSC strategic plan 2001/04). The HSC's aim is that OELs should:

  • control risks to health;

  • be readily understood/accessible;

  • be legally enforceable;

  • be comprehensive;

  • comply with EC legislation;

  • be flexible and able to take on board new developments in science and technology; and

  • provide incentives to reduce exposure.

    Maintaining the present system with minor modifications to the indicative criteria satisfies some, but not all, of these objectives, whereas the good practice options satisfy all of the objectives. Similarly, against the Revitalising aims of promoting better working environments, the positive engagement of small firms and encouraging partnerships on health and safety issues, maintaining the present system with minor modifications to the indicative criteria offers no improvement over the existing system.

    On the other hand, the good practice options do satisfy the Revitalising aims. They promote better working environments by emphasising the requirement of the COSHH Regulations to apply good practice and by linking good practice advice directly with OELs. A simplified OEL system and the provision of clear practical advice are the kinds of help that small firms have told HSC/E they need. And linking OELs with the style of guidance set out in COSHH essentials, including a simple checklist for employees, and making all the information freely available on the internet, will make it easier for safety representatives and individual employees to access the information they need. This approach will encourage partnerships as envisaged in the Revitalising strategy statement.

    Launching the HSC's proposals in April, Sandra Caldwell, director of HSE's health directorate said: "We want this review to start a debate on what everyone wants from occupational exposure limits. For example - should we link OELs to good practice advice that helps firms decide how to control chemicals? Should we change the way we set OELs? Would firms use a free internet database containing a list of OELs and linked to more information? By contributing to the debate, it will help us set up a robust system of limits that will help to control hazardous substances and contribute to HSC's Revitalising target to reduce occupational ill health by 20% by 2010." An HSC working group has been set up to consider responses to the HSC's proposed changes to the OEL system alongside other research on the operation of the current system. It will then make formal proposals for changes to the OEL framework. Subject to approval by the HSC, these will be published in a formal consultation document in 2003. Any changes to the COSHH Regulations would not occur until 2004.


    Box 1: OESs and MELs

    OESs and MELs are set on the recommendation of the Advisory Committee on Toxic Substances (ACTS), following assessment of the toxicological, occupational hygiene and analytical data by the Working Group on Assessment of Toxic Chemicals (WATCH) or the Working Group on European Exposure Limits (WEELs). The Committees have to consider, firstly, what type of limit is appropriate - OES or MEL - and, secondly, at what concentration the limit should be set.

    Where there is no European occupational exposure limit, the substance is first reviewed by WATCH. WATCH considers whether an OES is appropriate and, if so, what value should be recommended to ACTS. Setting an OES is the first option to be considered and WATCH reaches a decision based on a scientific judgement of the available information on health effects. But if WATCH decides that an OES (8-hour time-weighted average (TWA) or 15-minute short-term limit) cannot be established and a MEL is more appropriate, then consideration of the level at which to set the MEL passes to ACTS, since it involves socio-economic judgements, balancing risk to health against the cost and effort of reducing exposure.

    Where a European occupational exposure limit has to be transposed, WEELs takes account of the scientific evaluation of the Scientific Committee on Occupational Exposure Limits (SCOEL), the European body that recommends OELs to the EC. WEELs considers whether an OES or a MEL is appropriate, whether any existing limit complies with the European limit and whether there are reasons to recommend a substantially different limit. If a new or revised OEL is required, WEELs makes recommendations to ACTS. WEELs may also recommend to ACTS that a substance is referred to WATCH for a scientific opinion.

    Recommendations for OESs and MELs are made by ACTS to the HSC. Following public consultation, new OESs and MELs are added to the tables of EH40, which are then submitted to HSC for approval. It is at this stage that they are given legal status and come into force on the publication of EH40.

    Duties relating to OESs:

  • the standard must be met;

  • there is no requirement further to reduce exposure below the standard; and

  • the standard can be exceeded so long as steps are taken to meet it as soon as reasonably practicable.

    Duties relating to MELs:

  • the limit must be met;

  • exposure must be reduced as far below the limit as is reasonably practicable; and

  • the limit must not be exceeded.

    		•


    Box 2: Setting an OEL for Bromochloromethane

    Although there were no carcinogenicity studies on bromochloromethane, evidence on similar chemicals raised concern that it might be carcinogenic in animals. In view of this, it was agreed that the criteria for an OES were not met: it was not possible to identify, with reasonable certainty, a level of exposure that was judged to pose no significant risk to health.

    But the uncertainties in relation to the possibilities of serious health effects in humans were such that it was felt that the criteria for establishing an MEL were not met either: it was not established that the chemical had serious health implications for workers.


    Box 3: How COSHH Essentials works

    The assessment is based on a series of tick-boxes that lead the user through five steps.

    Step 1 - find the material safety data sheet for each chemical used and determine the task to be assessed, eg mixing, weighing, drying, storage.

    Step 2 - look at the three factors that identify the control approach:

  • the possible health effects from exposure - a chemical is assigned to a hazard group on the basis of risk phrases, eg R20 - "harmful by inhalation" - would put a chemical into hazard group B;

  • the amount in use - ie small, medium or large - guidance is given on choosing the appropriate category; and

  • how dusty or volatile the chemical is - ie low, medium or high - guidance is given on choosing the appropriate category.

    Step 3 - find the control approach using the information from steps 1 and 2. Risk matrices for each of the hazard groups identify the appropriate control approach:

  • general ventilation;

  • engineering control;

  • containment; or

  • special.

    For each approach there is a general control guidance sheet.

    Step 4 - find the task-specific control guidance sheets. In addition to the general advice provided by step 3, further guidance is given in 60 single-page sheets detailing practical control measures depending on: the task; whether the chemical is solid or liquid; and how much is being used. For example, if the appropriate control approach has been determined as "containment", and users are mixing medium amounts of a solid, they are referred to guidance sheet 317. The task-specific control guidance sheets have a common format giving advice on:

  • access to the work area;

  • design of the process and equipment;

  • maintenance;

  • examination and testing;

  • cleaning and housekeeping;

  • personal protective equipment;

  • training supervision; and

  • sources of further information.

    The sheets also contain an employee checklist for making the best use of controls.

    Step 5 - implement the action and review. This step is broken down into stages:

  • assess other chemicals used and tasks;

  • plan the implementation;

  • consider safety and environmental hazards;

  • consider other aspects of COSHH, such as health surveillance and exposure monitoring;

  • implement the control measures; and

  • review the assessment.

    • 1"Discussion document on Occupational Exposure Limits (OEL) framework", DDE19, HSE Books, free, or www.hse.gov.uk/condocs. Comments should be sent to Sara Wassell, Health Directorate, Chemical Policy Division, HSE, 6SW, Rose Court, 2 Southwark Bridge Road, London SE1 9HS or email CRAU@hse.gsi.gov.uk to arrive by 31 July 2002.

    2"COSHH Essentials: easy steps to control chemicals", HSG 193, HSE Books, ISBN 0 7176 2421 8, £25.

    3"Occupational Exposure Limits 2002", EH40, HSE Books, ISBN 0 7176 2083 2, £10.50; "Summary criteria for Occupational Exposure Limits 1996 - 1999", EH64, HSE Books, ISBN 0 7176 2469 2, £40; "Summary criteria for occupational exposure limits: 2000 supplement", EH64 supplement, HSE Books, ISBN 0 7176 1800 5, £10; and "Summary criteria for occupational exposure limits: 2001 supplement", EH64 supplement, HSE Books, ISBN 0 7176 2070 0, £10.

    4www.coshh-essentials.org.uk/.