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Threshold Limit Values (TLVs) have been published by the American Conference of Government Industrial Hygienists (ACGIH) since the 1940s, and have been very influential in much of Europe, Scandinavia, Japan and in developing countries. According to HSE staff, "Britain has been producing its own exposure limits for about 11 years, and before that reprinted the ACGIH threshold limit value (TLV) list as guidance. (When COSHH came into force in 1989) many TLVs were adopted as OESs without further review ... Britain has set exposure limits following reviews of about 150 substances. Of the 150, about 100 have been given OESs and 50 have been given MELs. About 350 OESs remain which were simply taken from the TLV list."

In 1988 American occupational health experts exposed the influence of chemical companies over the ACGIH's TLV committee, and the secrecy that surrounds their work. A 1986 study, Documentation of the Threshold Limit Values and Biological Exposure Indices by Castleman and Ziem, found that for 104, or over one-sixth, of the under 600 substances listed, "important or total reliance was placed on unpublished corporate communications." ACGIH classified 11 substances as human carcinogens, and 40 as suspected human carcinogens. The equivalent German classification lists 17 human and 42 suspected human carcinogens.

The ACGIH is not part of the US government, but a voluntary organisation. In the mid-1980s, the annual budget of the TLV committee was just $30,000, so it relied heavily on the voluntary work of its committee members. In return, Castleman and Ziem suggest, industry was rewarded with high TLVs which reduced the costs of regulation to the chemical industry. On the other hand, only occasional token efforts were made to get a trade union industrial hygienist onto the committee.

Castleman and Ziem were concerned that not only were chemical company representatives setting TLVs for substances that their own firms manufactured, but that the data they used to set limits was often supplied by the companies but never published. This means that independent scientists have no idea how good these studies were. They say, "The TLVs are assumed by many to be first world, 'first class' guidelines for worker protection. The consequences of such misplaced confidence in the TLVs are profound and global. The credibility of the ACGIH limits as scientifically, independently and verifiably determined persists as an obstacle to a better standard of worker protection ... It is time that we all openly acknowledge the political nature of decisions by unexposed scientists and regulators regarding maximum levels of chemicals to which other humans can knowingly be exposed. The decision process therefore must not only be freed from undue corporate influence; it must also include substantial participation by representatives of exposed persons."

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