Biological Exposure Indices
Exposure Indices · Exposure Indices overview
Biological Exposure Indices (BEIs) are reference values published by ACGIH that indicate the concentration of a determinant in a biological matrix that would be expected in workers exposed by inhalation at the corresponding airborne occupational exposure limit (TLV-TWA).
What a BEI is
A BEI is a guideline value, not a statutory limit. It is derived by ACGIH from the relationship between airborne exposure at the TLV-TWA and the resulting biomarker concentration in the average worker, accounting for inhalation absorption only. Where the substance has significant dermal absorption, exceeding the BEI does not necessarily mean the airborne TLV was exceeded.
BEI vs HSE BMGV
HSE Biological Monitoring Guidance Values (BMGVs) are the UK equivalent. They are also advisory, also expressed per gram of creatinine for urinary biomarkers, and broadly numerically similar to BEIs where both exist. UK programmes default to BMGV where one is published; otherwise to the ACGIH BEI.
How to use a BEI
BEIs are applied to group results — typically the geometric mean — and to individuals only with care. A single worker above the BEI is investigated; a cohort GM above 50% of the BEI is treated as a control-review trigger by most UK occupational hygiene programmes.
Frequently asked questions
Are BEIs legally enforceable in the UK?
No. They are advisory and used by HSE inspectors and occupational hygienists as the benchmark of adequate control under COSHH regulation 7.
What does it mean if a worker is above the BEI?
It triggers an investigation of task, controls and dermal hygiene. A single result above the BEI is not, by itself, proof of harm.
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