Exposure Standards for Chemicals

Regulatory agencies set the limits to which workers can be exposed to particular hazards. These are known as "Exposure Standards", "Occupational Exposure Limits" ["Threshold Limit Values" (TLVs) and "Short Term Exposure Limit" (STELs)]. They are numerical values (e.g. parts per million and milligrams per metre cubed for chemical fumes; dBA for noise levels, ºC for temperature) which represent the exposure levels to which workers may be repeatedly exposed and are regarded as an "acceptable risk".

How are they set?

There is a three-stage process to standard setting in occupational health and safety:

1: Hazard Identification - Identification of anything in the working environment that may cause harm.

2: Risk Assessment - an assessment of the likelihood of injury or illness as a result of exposure to that hazard.

Tests in laboratories, or by epidemiological studies may provide evidence of a link between exposure and dose at varying levels and any effect or response. The dose response relationship provides the technical information on which to base the setting of Standards for "safe" exposure.

3: Risk Evaluation - This process is a social one. Reference to given technical information arrived at in the Risk Assessment stage is only part of the process of evaluating risk and determining what is an "acceptable" level of risk or exposure standard.

The process often involves a decision being reached through consensus amongst representatives of government, health and safety professionals, unions and employers (such as on the National Occupational Health and Safety Commission - now SafeWork Australia).
NOTE: There have been no changes to Australia's Exposure Standards for some years - the system has broken down - this means that while exposure standards to some hazardous substances may be being reduced internationally, Australian workers are still being exposed to the higher, old, exposure standards. In 2012/2013 SafeWork established a working group to consider how best to ensure that exposure standards are kept up to date.

Standards Australia also release Standards of 'acceptable exposure', although committees established for this purpose generally have only government and industry representatives.

Generally, the exposure standard or TLV/STEL is determined by a trade-off or balancing of the risks and costs of removing those risks. The following criteria is considered by those making decisions on what is an "acceptable" level of risk:

• The level of knowledge about the hazard
• The extent of knowledge of the risk of exposure
• The costs of "living with" the hazard and associated risk:
  - extent of injury/disease;
  - extent of social effects on injury/disease;
  - extent of demand on and cost of medical and like services;
  - costs of compensation premiums and common law claims.
• The level of knowledge of ways to control the hazard and reduce exposure levels;
• The availability of ways to control the hazard and reduce exposure levels;
• The cost to industry of controlling the hazard and reducing exposure levels;
• The implications of industry meeting that cost.

Therefore the health and safety of workers is not always paramount in the setting of safe standards. A number of factors point to the limited reliability of the standard-setting process determining absolute "safe" exposure levels.

• Judgements made in the risk evaluation stage of the process are often subjective, and not objective;
• The "safe" exposure level is determined by a process based on a concept of so-called "acceptable risk";
• The technical information made available to those evaluating the risk is often controversial (and sometimes fraudulent);
• The technical information illustrated by dose-response relationships makes predictions for groups of subjects, showing what is likely to occur "on average" - they cannot predict for individuals;
• The dose-response relationships indicate a clear level of risk for equivalent populations - not all workers' situations are the same, however;
• Technical information used to evaluate risk generally results from tests which only assess short term or acute effects;
• Exposure standards are set for individual hazards, and yet workers are generally exposed to more than one hazard at a given time - the effects of combined exposure are generally unknown;
• Exposure standards for chemicals are set for a "normal" working day of 8 hours - allowing the body 16 hours to "recover". Working arrangements are changing, however, and 12 hour shifts have become more common.
• As more information becomes available and there are advances in control technology, standards have inevitably been lowered;
• For a standard to have some effect in adequately protecting workers' health and safety it must be strictly enforced (this has implications for the role of Inspectors and prosecution procedures).

More information

Important Chemicals Information