Recommended or mandatory occupational exposure limits (OELs) have been developed in many countries for airborne exposure to gases, vapours and particulates. The most widely used limits, called threshold limit values (TLVs), are those issued in the USA by the American Conference of Governmental Industrial Hygienists (ACGIH).

For airborne exposures, there are three types of limits in common use:

• the time-weighted average (TWA) exposure limit - the maximum average concentration of a chemical in air for a normal 8-hour working day and 40-hour week;
• the short-term exposure limit (STEL) - the maximum average concentration to which workers can be exposed for a short period (usually 15 minutes);
• the ceiling value - the concentration that should not be exceeded at any time.

In addition, biological exposure indices (BEIs) represent the concentration of chemicals in the body that would correspond to inhalation exposure at a specific concentration in air.

The following texts provide information on the agency responsible for the establishment and publication of exposure limits in each country with an Internet link to a table or database containing the exposure limit values.

Maximum permissible concentrations or threshold level values (TLVs) are listed (in Spanish) in Annex III of Decree No.351/79 introducing regulations under Law Nº 19.587 concerning occupational safety and health.

Exposure standards are available on the Hazardous Substances Information System (HSIS) database of the Australian Safety and Compensation Council (formerly the Australian National Occupational Health and Safety Commission, NOHSC).

Information is provided on substances that have been classified in accordance with the Approved Criteria for Classifying Hazardous Substances [NOHSC:1008(2004)] 3rd Edition and/or have National Exposure Standards declared under the NOHSC Adopted National Exposure Standards for Atmospheric Contaminants in the Occupational Environment [NOHSC:1003(1995)] or subsequent updates.

The HSIS provides access to two data sets, one for hazardous substance information and the other for exposure standard information. Data for substances that are common to both data sets are linked. Both data sets can be searched using a range of search criteria. Search results (including the full data sets) can be printed or saved electronically.

Austrian occupational exposure limits are based on international and national sources such as the American Conference of Governmental Industrial Hygienists and the German MAK-Commission. The limits are fixed by the Bundesministerium für Wirtschaft und Arbeit (BMWA, Ministry of the Economy and Labour) and are published in the Austrian Governmental Journal as an ordinance entitled Grenzwerte für Arbeitsstoffe und über krebserzeugende Arbeitsstoffe (Grenzwerteverordnung 2001 - GVK 2001).

Occupational exposure limits (valeurs limites d'exposition professionnelle) are issued by the Ministry of Employment and Work and are listed in Annex 1 of the Arrêté royal du 11 mars 2002 relatif à la protection de la santé et de la sécurité des travailleurs contre les risques liés à des agents chimiques sur le lieu de travail.

Exposure limits in Brazil are given in the Tabela de Limites de Tolerância in Annex No.11 of Regulatory Standard NR N-15. They are issued under the authority of Decree (Portaria) No.3214 of 8 June 1978.

Exposure limits are listed (in Bulgarian) in Decree No.13 of 30 December 2003 on the protection of workers against the risks of exposure to chemical agents at work.

Occupational exposure limits in Canada are regulated within each Province.

In Alberta, exposure limits are listed in the Chemical Hazards Regulation (Alberta Regulation 393/88).

In British Columbia, exposure limits are generally determined with reference to the Threshold Limit Values (TLVs) adopted by the American Conference of Governmental Industrial Hygienists (ACGIH). They are listed here. An explanation of the procedure for ensuring that adopted exposure limits are appropriate for workers in British Columbia is given here.

In Ontario, exposure limits are listed in Regulation 833, 1999 - Control of Exposure to Biological or Chemical Agents.

In Québec, exposure limits are listed in the Règlement sur la santé et la sécurité du travail.

Exposure limits are given in the Reglamento sobre Condiciones Sanitarias y Ambientales Básicas en los Lugares de Trabajo (1992).

Exposure limits for Cyprus are listed (in Greek) in the Safety and Health at Work (Chemical Agents) Regulations of 2001.

Exposure limits are listed in Danish in Grænseværdier for stoffer og materialer and in English in Limit Values for Substances and Materials.

In Estonia, occupational exposure limits are prepared and endorsed by the Ministry of Social Affairs. The limits are set with reference to current European Union and Swedish occupational exposure limits and are listed (in Estonian) here.

The legal basis for the preparation of occupational exposure limits and biological limits in the European Union is contained in Directive 98/24/EC on chemical agents and Directive 2004/37/EC on carcinogens and mutagens. Indicative Occupational Exposure Limit Values (IOELVs) are adopted through Commission Directives while Binding Occupational Exposure Limit Values (BOELVs) are adopted through Council and European Parliament Directives.

IOELVs listed in Directives 91/322/EEC and 2000/39/EC and BOELVs listed in Directives 98/24/EC, 99/38/EC and 2003/18/EC are available here.

On 7 February 2006, the Commission adopted Directive 2006/15/CE establishing a second list of Indicative Occupational Exposure Limit Values (IOELVs) in implementation of Council Directive 98/24/EC and amending Directives 91/322/EEC and 2000/39/EC. This Directive establishes IOELVs for 33 substances following an evaluation by the Scientific Committee on Occupational Exposure Limits (SCOEL) of the latest available scientific data.

Details of exposure limit systems in European Union Member States (and in some non-Member States) may be found here.

Concentrations of impurities in workplace air known to be hazardous and corresponding limit values for biological exposure indicators are published by the Finnish Ministry of Social Affairs and Health. They are listed (in Finnish and Swedish) here and there is a brief introductory summary in English here.

Occupational exposure limits are published in the Order of 30 June 2004 (modified by the Order of 9 February 2006) establishing a list of indicative occupational exposure limits and in Decree No. 2006-133 of 9 February 2006 fixing binding occupational exposure limits for certain chemical agents in workplace air.

The values are also published by the Institut National de Recherche et de Sécurité (INRS) in Valeurs limites d'exposition professionnelle aux agents chimiques en France, Aide-mémoire technique ED 984.

Rules for limiting exposure to hazardous substances in the workplace and a list of occupational exposure limits are published in Germany by the Federal Institute for Occupational Safety and Health (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin - BAuA) in Technical Rules for Hazardous Substances (Technische Regeln für Gefahrstoffe) TRGS 900: Occupational exposure limits (Arbeitsplatzgrenzwerte). This document was reissued in January 2006 with significant changes to the list of substances for which occupational exposure limits have been assigned. In addition, the publication removed the previous MAK and TRK designations from substances. The current list is divided into Category I and II substances:
Category I: substances for which the local effect has an assigned OEL or substances with a respiratory sensitizing effect.
Category II: substances with a resorptive effect.
BAT values (Biologische Arbeitsstofftoleranzwerte - Biological Tolerance Values) are listed in TRGS 903.

Exposure limits are listed in A munkahelyek kémiai biztonságáról szóló 25/2000. (IX. 30.) EüM-SZCSM rendelet [Ordinance No.25/2000, of 30 Sept., concerning the chemical safety of workplaces]. A copy can be found here.

Occupational exposure limits are listed by Ireland's National Authority for Occupational Safety and Health in Schedule 1 to the 2002 Code of Practice for the Safety, Health and Welfare at Work (Chemical Agents) Regulations, 2001 .

Occupational exposure limits for chemical substances are recommended by the Japan Society for Occupational Health (JSOH). Current values are listed in the Journal of Occupational Health.

Exposure limits in Luxembourg are listed in Regulations concerning the protection of the health and safety of workers against the hazards of chemical agents, carcinogens and mutagens in the workplace, July 2002.

Occupational exposure limits in the Netherlands are set by the Deputy Minister for Social Affairs and Employment. Exposure limit values and information on their status and revision may be found in the Databank of the Social and Economic Council of the Netherlands (SER).

Exposure limits are available in Workplace Exposure Standards effective from 2002 published by the Occupational Safety and Health Service of the Department of Labour.

Values are provided for workplace exposure standards for atmospheric contaminants, biological exposure indices and workplace exposure standards for noise.

Administrative standards for contaminants in workplace air (Veiledning om administrative normer for forurensning i arbeidsatmosfaere) are available from the Norwegian Labour Inspection Directorate (Arbeidstilsynet).

Exposure limits are listed (in Slovak) in Order No.45/2002 of 16 Jan. 2002 on health protection while working with chemical agents and in Order No.46/2002 of 16 Jan. 2002 on health protection while working with carcinogenic and mutagenic agents.

Occupational Exposure Limits for airborne pollutants in the Republic of South Africa are issued by both the Department of Labour and the Department of Minerals and Energy. Values are listed on the site of the South Africa Institute of Occupational Hygiene.

Occupational exposure limits are published by the National Institute for Occupational Safety and Health (Instituto Nacional de Seguridad e Higiene en el Trabajo, INSHT) in Límites de exposición profesional para agentes químicos en España.

Exposure limits are listed in Swedish in Hygieniska gränsvärden och åtgärder mot luftföroreningar (AFS 2005:17) and in English in Occupational Exposure Limit Values and Measures Against Air Contaminants (AFS 2005:17).

Swiss occupational exposure limits are published by the Swiss Accident Insurance Institute (SUVA) in SUVA - Valeurs limites d'exposition aux postes de travail, published annually. They are available in French and in German.

As from April 2005, the former Maximum Exposure Limits (MELs) and Occupational Exposure Standards (OESs) are replaced with a single type of limit - the Workplace Exposure Limit (WEL). Values are listed in the latest edition of the Health and Safety Executive (HSE) Guidance Note EH40 Workplace exposure limits.

This list is legally binding. It reproduces the list of workplace exposure limits (WELs) that have been approved by the Health and Safety Commission.

Recommended exposure limits are developed and periodically revised by the National Institute for Occupational Safety and Health (NIOSH). These recommendations are then published and transmitted to the Occupational Safety and Health Administration (OSHA for use in promulgating legal standards.

Permissible exposure limits are published in the U.S. Code of Federal Regulations, Occupational Safety and Health Standards on Toxic and Hazardous Substances, 29 CFR 1910.1000, Tables Z-1, Z-2, and Z-3.

Permissible exposure limits and NIOSH recommended exposure limits are also available in the NIOSH Pocket Guide to Chemical Hazards.

Threshold limit values (TLVs) and biological exposure indices (BEIs) are also issued by the American Conference of Governmental Industrial Hygienists (ACGIH). Information on the determination and use of these values and their availability may be found on the ACGIH website.

Some States also have their own exposure limits, for example:

In California, permissible exposure limits for chemical contaminants are listed in the California Code of Regulations, Control of Hazardous Substances Order.

In Michigan, permissible exposure limits for air contaminants are listed in the Occupational Health Standards published by the Department of Consumer and Industry Services.

In Minnesota, the Minnesota Department of Labor and Industry publishes permissible exposure limits for air contaminants.

In Washington, permissible exposure limits for air contaminants are published in the Safety and Health Rules of the Washington State Department of Labor and Industries.