Biological exposure index (BEI)

Air monitoring measures what is in the workplace air, but it cannot show what a particular person absorbed. Skin contact, ingestion, hard physical work that increases breathing, respirator leakage and off-the-job exposure can all change the dose. Biological monitoring measures what actually entered the body, and a BEI is the reference value for judging that result.

BEIs are set to represent the level typically seen in healthy workers who have been exposed to the chemical at the Threshold limit value (TLV) by inhalation. They come with details on when to collect the sample, such as the end of a shift or the end of the work week, and which determinant to measure. Results are interpreted by a qualified occupational health professional, since diet, medications and smoking can affect many biomarkers.

A BEI is a guideline, not a legal limit, and exceeding it does not by itself mean illness has occurred. It is a prompt to review work practices, look for unexpected routes of exposure and strengthen controls. It is especially helpful for chemicals with a Skin notation, where air results may understate exposure.

Few chemicals have a BEI, and the SDS rarely lists one. When biological monitoring is used, it should be part of a medical surveillance program with proper consent and confidentiality.