Atmospheric limit values for chemicals used in the workplace

The occupational exposure limits (OEL) recommended by ANSES are air concentrations of a chemical that almost all workers can breathe during a specified period without any known risk, at the time of the expert appraisal, of impairment to their health. Levels are determined on the assumption that the population of exposed workers is homogeneous, and includes neither children nor the elderly.

Concentration levels are determined based on scientific data from human studies (epidemiological and clinical studies) or experimental animal studies (toxicological studies).

Approach followed by the Agency

In order to propose these atmospheric values, ANSES strives to assess, on the basis of the scientific and technical information available:

• the health effects of chemicals, so as to recommend limits to be applied for protecting the health of workers;
• the relevance of assigning a "skin" notation; this reference is given to substances for which dermal absorption leads to a significant increase in exposure and causes a systemic effect;
• the relevance of assigning a “noise” notation; this reference is given to substances for whichthere is a certain level of evidence on their possible ototoxic effect in the event of co-exposure to noise ;
• the measurement methods available, in order to determine those that can be technically applied for the purposes of comparison with the recommended OELs.

For a given substance, three types of occupational exposure limits can be recommended:

• the 8-hour occupational exposure limit value or 8h-OEL, which is designed to protect, in the medium and long term, the health of workers exposed regularly and for the duration of a working life, from the chemical in question. Unless stated otherwise, this is the limit of the time-weighted average concentration of a chemical agent, in the air in a worker’s breathing zone, over the course of an 8-hour shift; 
•  a Short-term limit value (15 min-STEL) which aims to protect workers from adverse health effects (immediate or short-term toxic effects such as irritation) due to exposure peaks. This is the limit of the time-weighted average of the concentration of a chemical in the worker's breathing zone over a 15-minute reference period (unless stated otherwise) during the peak of exposure, irrespective of its duration;
• a Ceiling value: this is the limit of the concentration of a chemical in the worker's breathing zone that should not be exceeded at any time during the working period. It mainly concerns agents known to be strong irritants or corrosive, or that may cause a serious and potentially irreversible effect in the very short term. Specific analytical measurements are used to determine this value.

These three values are expressed either:

• in mg.m^-3, i.e. in milligrams of chemical per cubic metre of air and in ppm (parts per million), i.e. in cubic centimetres of chemical per cubic metre of air, for gases and vapours;
• in mg.m^-3 only, for liquid and solid aerosols;
• in f.cm^-3 (fibres per cm³) for fibrous materials.

Inventory of methods available for measuring exposure levels

For every substance studied, ANSES supplements the work to establish OELs by cataloguing the protocols available for measuring the occupational exposure levels. These protocols are grouped according to the methods used. The quality of these methods and their applicability to the measurement of exposure levels for comparison with an OEL are assessed, particularly with regards to their compliance with the performance requirements in Standard EN 482 "Workplace atmospheres - General requirements for the performance of procedures for the measurement of chemical agents"and their level of validation.

These methods are classified as follows:

• category 1A: the method has been recognized and validated (all of the performance criteria in the NF-EN 482 Standard are met);
• category 1B: the method has been partially validated (the essential performance criteria in the NF-EN 482 Standard are met);
• category 2: the method is indicative (essential criteria for validation are not clear enough);
• category 3: the method is not recommended (essential criteria for validation are lacking or inappropriate).

A detailed comparative study is conducted of the methods classified in Category 1A, 1B and 2 with respect to different data on validation and technical feasibility in order to recommend the most appropriate method(s) for measuring concentrations for the purpose of comparison with the OELs.

Values to supplement the atmospheric OELs

The Agency is also required to decide whether or not a "skin" notation should be assigned. This indicates the need to take the dermal route into account in the exposure assessment in order to implement appropriate preventive measures (wearing gloves, evaluation of surface contamination, etc.). This reference alerts to the fact that the dermal route of exposure can potentially cause health effects independently of the atmospheric limit values. Indeed, the combination of the two routes of exposure (inhalation and dermal) may exceed the dose considered not to induce any effect on health.

Finally, when deemed appropriate, in addition to the atmospheric OELs, ANSES rules on any information that may be useful for establishing biological monitoring of exposure by occupational physicians.