The legislative basis for OELs is the Chemicals Acts (Chemikaliengesetz ^[238]) with its Dangerous Substances Regulation (Gefahrstqffverordnung ^[239]). The Act was last amended on 13 May 2004. The new Ordinance on Hazardous Substances came into force on 1 January 2005. hi addition to these basic acts, so called Technical Rules for Hazardous Substances provide for additional information when dealing with hazardous substances and list occupational exposure limit values (TRGS 900 ^[240] and 903 ^[241]), carcinogenic, mutagenic and substances toxic to reproduction (TRGS 905 ^[242]), or sensitising substances (TRGS 907 ^[243]). The TRG 900 (MAK and TRK values) refers to about 900 substances or groups of substances, though the number of substances actually covered is much higher (for example, Beryllium and its compounds).

Types of Occupational Exposure Limits until 31 December 2004. Until 31 December 2004, three limit values were in use in Germany:

• Maximum Workplace Concentrations (Maximale Arbeitsplatzkonzentrationen - MAK)

• Technical Guidance Concentrations (Technische Richtkonzentrationen -TRK), and

• Biological Tolerance Value for occupational exposures (Biologische Arbeitsstofftoleranzwerte - BAT).

The first occupational exposure limit values were published in 1886. In 1938, about 100 OELs were presented during a congress in Frankfurt. In 1958, the first MAK-list was published; the values mainly based on the US TLV list. Since 1969, the MAK list has been published annually and independently from the TLV list.

New limit value concepts from 1 January 2005. Since 1 January 2005, with the...