The biological limit describes up to which toxicologically, occupational medicine derived concentration of a substance, its metabolite or a stress indicator in the corresponding biological material the health of employees is generally not impaired. If the biological limit of a substance is exceeded once, no health impairment must occur. Exceptions to this are acutely toxic substances for which the biological limit must not be exceeded. A list of the biological limits can be found in the technical rules for hazardous substances (TRGS) 903.

Sources: ordinance on hazardous substances, technical rules for hazardous substances 903