Occupational Exposure Limits: What are they and what do they mean?

By Mfanimpela Godfrey Kubheka

What every employer and employee needs to know about Occupational Exposure Limits (OELs).

Any substance or mixture of substances that may be toxic, harmful, irritant, corrosive, asphyxiant for which an occupational exposure limit is prescribed or an occupational exposure limit is not prescribed but there is sufficient scientific (toxicological and epidemiological information to be specific) to deem it hazardous to human health is a hazardous chemical substance or agent (HCS). There are many hazardous chemical substances in industry today than there were in the 19th century; however many of these chemicals do not have any occupational exposure limits prescribed for them, the information used to set the existing occupational exposure limits can sometimes be incomplete (AIHA,2006) and each year the number of new hazardous chemical substances that enter the market and somehow end up in the lungs, blood stream and other vital organs of workers keeps on growing.

Occupational exposure limits (OELs) come in various forms; there are mainly four categories of OELs. Regulatory, Authoritative, Internal and Working OELs. Regulatory OELs are those that are set and enforced by regulatory bodies or agencies such as the Department of Employment and Labour (in South Africa) or their American counter-part, the Occupational Safety and Health Administration (OSHA). In South Africa, OELs are set by the Minister of the Department of Employment and Labour (The Chief Inspector as advised by the Advisory Council for Occupational health and Safety to be specific) and are promulgated under the Occupational Health and Safety Act, Act 85 of 1993 and its Regulations. Other regulatory bodies such as the Department of Mineral Resources (DMR) have industry specific OELs which are promulgated under the Mine Health and Safety Act, Act 29 of 1996. In Europe, OELs are established by the European Commission (EC) and
its member countries. Authoritative OELs are those which are set and recommend by organizations such as the American Conference of Governmental Industrial Hygienists (ACGIH) publishes its own guidelines in a form of Threshold Limit Values (TLVs) (AIHA, 2006). Another organization of note is the the National Institute for Occupational Safety and Health (NIOSH) which sets what is called recommended exposure limits (RELs); it is important to note that OSHA sets and enforces permissible exposure limits (PELs). Internal OELS, are those which are developed internally by organizations or entities. Due to the fact that most of the chemicals used today do not have any occupational exposure limits, in fact; according to the American Industrial Hygiene Association, (2006), "OELs are available for only about 600 of the 70,000 of the chemicals used in industry." There is a general lack of toxicological and epidemiological information for most of them; some employers develop their own occupational exposure limits. Working OELs, are those that are normally identified by occupational hygienists in the absence of any regulatory, authoritative or internal OELs. These are identified in order to distinguish acceptable from unacceptable exposures, they are created during or in the course of an exposure assessment and are set to be informal (AIHA, 2006).

Source: Perry W. Logan, 2013
https://en.wikipedia.org/wiki/File:Hierarchy_of_Occupational_Exposure_Limits.JPG

"OELs are available for only about 600 of the 70,000 of the chemicals used in industry."

In South Africa, the Hazardous Chemical Substances Regulations of 1995 provide clear guidelines on OELs and how they are set and enforced. Under these regulations, occupational exposure limits are classified into various types namely: occupational exposure limit-recommended limit (OEL-RL), occupational exposure limit-control limit (OEL-CL), short-term and long-term occupational exposure limit. Short-term Exposure Limit (STEL) is a 15-minute TWA exposure that should not be exceeded at any time during a working day, even if the 8-hour TWA is within the TLV-TWA. The Time-weighted Average (TWA) is the TWA concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day after day, for a working lifetime without adverse effect.
Its is important to note that exposure limits prescribed in tables I and II of the Hazardous Chemical Substances Regulations (HCS), 1995 as promulgated under the Occupational Health and Safety Act, Act 85 of 1993 only apply or relate to personal exposure to substances hazardous to health in the air of the workplace and only consider inhalation as the route of entry. It is also important to note that there are limitations to the application of OELs which are discussed in great length in the HCS Regulations, 1995.

An occupational exposure limit-recommended limit (OEL-RL) is the concentration of an airborne substance, averaged over a reference period, at which, according to current knowledge, there is no evidence that it is likely to cause adverse health effects or be injurious to employees if they are exposed via inhalation. An occupational exposure limit-control limit (OEL-CL) is the the maximum concentration of an airborne substance averaged over a reference period, to which employees may be exposed by inhalation under any circumstances. This OEL must be specified together with the appropriate its reference period (Usually 8 hours). It is important for employers to note that the Act puts or imposes a duty on them to determine reasons as to why an OEL has been exceeded in the workplace, take all reasonable precautions and to exercise all due diligence to ensure that exposure is kept as far as reasonably practicable below and OEL-CL. This is where most employers get away with murder. Many employers resort to issuing employees with personal protective equipment (PPE) without exercising their duty as mentioned above. Even though OELs are not perfect and different situations may require different strategies, they are all what both employers and employees have as guidance towards dealing airborne concentration of hazardous chemical substances.

N:B: Under the Draft HCS Regulations of 2018, an OEL-CL is referred to an occupational exposure limit-maximum limit while and OEL-RL is referred to an occupational exposure limit-restricted limit as confusing these changes may be to the veteran occupational hygienist, they will have to be adhered to should the new regulations be promulgated. Remember that just because there is no audit finding on a non-compliance does not make it correct, ethically or otherwise to continue operating under conditions of non-compliance where the health and well-being of other humans may be at stake. Everyone has an obligation to do the right thing and protect worker health and safety.



Mfanimpela Godfrey Kubheka is a Public Health Consultant and plays various leadership, management and entrepreneurial roles within the health sector. He has interests in Monitoring and Evaluation, Health Policy, Leadership, Occupational Hygiene, Environmental and Occupational Health.