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The Occupational Safety systems in the United States vary from state to state. Here, Information is given on major providers of the Occupational Exposure Limits in the USA - ACGIH, OSHA, and NIOSH.


The American Conference of Governmental Industrial Hygienists (ACGIH) publishes since 1946 Maximum Allowable Concentrations (MAC), which were later renamed to "Threshold Limit Values" (TLVs). Threshold Limit Values are defined as an exposure limit "to which it is believed nearly all workers can be exposed day after day for a working lifetime without ill effect". The ACGIH is a professional organization of occupational hygienists from universities or governmental institutions. Occupational hygienists from private industry can join as associate members since shortly.

Today, nine ACGIH committees focus their energies on a range of topics such as agriculture safety and health, air sampling instruments, bio-aerosols, biological exposure indices, construction, industrial ventilation, infectious agents, chemical substance TLVs, and physical agent TLVs. Once a year, the different committees propose new threshold limits or best working practice guides. The list of TLVs includes more than 700 chemical substances and physical agents, as well as dozens of Biological Exposure Indices for selected chemicals. Substances are nominated by the TLV Committee based on new occupational exposure data or requests of governmental organizations, workers, industry etc.. The committee decides which substances selected for consideration are to be studied and votes at least once a year on action items.

The committee has developed selection criteria for substances, taking into account scientific evidence or workplace experience. Every TLV or BEI is developed and based on the available, relevant, scientific data for that agent. Some TLVs include also skin and carcinogenity notations and Biological Exposure Indices.

The ACGIH defines different TLV-Types as there are:
• Threshold Limit Value - Time-Weighted Average (TLV-TWA): the time-weighted average 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, without adverse effect.
•Threshold Limit Value-Short - Term Exposure Limit (TLV-STEL): the concentration to which it is believed that workers can be exposed continuously for a short period of time without suffering from
•chronic or irreversible tissue damage, or •narcosis. STEL is defined as a 15-minute TWA exposure, which should not be exceeded at any time during a workday
•Threshold Limit Value - Ceiling (TLV-C): the concentration that should not be exceeded during any part of the working exposure.
•Excursion Limits. There is a general excursion limit recommendation that applies to those TLV-TWAs that do not have STELs. Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the TLV-TWA, provided that the TLV-TWA is not exceeded.

ACGIH-TLVs do not have a legal force in the USA, they are only recommendations. OSHA defines regulatory limits. However, ACGIH-TLVs and the criteria documents are a very common base for setting TLVs in the USA and in many other countries. ACGIH exposure limits are in many cases more protective than OSHA's. Many US companies use the current ACGIH levels or other internal and more protective limits.

Internet Links
Reference resource


The Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labour (USDOL) publishes Permissible Exposure Limits (PEL). PELs are regulatory limits on the amount or concentration of a substance in the air, and they are enforceable. The initial set of limits from 1971 was based on the ACGIH TLVs. An attempt to extend the number of TLV to other widely used chemicals was proposed by OSHA in 1989. OSHA additionally proposed in 1992 to apply most of these new and revised limits to construction, maritime, and agriculture. OSHA currently has around 500 Permissible Exposure Limits (PELs) for various forms of approximately 300 chemical substances, many of which are widely used in industrial settings. Existing PELs are contained in a document called "29 CFR 1910.1000", the air contaminants standard.

If OSHA determines that a specific standard is needed, any of several advisory committees may be called upon to develop specific recommendations. There are two standing committees, and ad hoc committees may be appointed to examine special areas of concern to OSHA. All Advisory committees, standing or ad hoc, must have members representing management, labour, and state agencies, as well as one or more designees of the Secretary of Health and Human Services. The two standing advisory committees are:
•National Advisory Committee on Occupational Safety and Health (NACOSH), which advises, consults with, and makes recommendations to the Secretary of HHS and to the Secretary of Labor on matters regarding administration of the Act.
•Advisory Committee on Construction Safety and Health, which advises the Secretary of Labor on formul ation of construction safety and health standards and other regulations.

OSHA uses in a similar way as the ACGIH the following types of OELs: TWAs, Action Levels, Ceiling Limits, STELs, Excursion Limits and in some cases BEIs.


The National Institute for Occupational Safety and Health (NIOSH) has the statutory responsibility for recommending exposure levels that are protective to workers. NIOSH has identified Recommended Exposure Levels (RELs) for around 700 hazardous substances. These limits have no legal force. NIOSH recommends their limits via criteria documents to OSHA and other OEL setting institutions.

Types of RELs are TWA, STEL, Ceiling, Biological Exposure Indices. The recommendations and the criteria are published in several different document types, such as Current Intelligent Bulletins (CIB), Alerts, Special Hazard Reviews, Occupational Hazard Assessments and Technical Guidelines.

Other US OEL publishers
Other exposure limits exist in the USA, published by organisations including:
•The American Industrial Hygiene Association (AIHA);
•The MSHA (Mine Safety and Health Administration);
•The American National Standards Institute (ANSI);
•The U.S. Navy.

Internet Links
TLV and BEI Guidelines
Some downloadable TLV and BEI documents

NIOSH's documents and lists

This information is intended for guidance only.



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UV Adhesives, Selective Soldering, PC Board Handling Conveyors and other products / technical services. We offer UV adhesives and conveyors