Isocyanate Biological Monitoring

Isocyanate biological monitoring measures urinary diamines — MDA, TDA, HDA, IPDA — as proxies for absorbed dose of MDI, TDI, HDI and IPDI. It is the standard verification method for spray painters, PU foam operators and coatings manufacturers in the UK.

Why isocyanates need biomonitoring

Isocyanates are skin-sensitisers and respiratory sensitisers, with a workplace exposure limit (WEL) for all isocyanates of 0.02 mg/m³ (15-min) and 0.005 mg/m³ (8-hour TWA) expressed as NCO. They absorb significantly through skin, so air monitoring alone systematically misses dermal uptake. Urinary diamine biomonitoring captures both routes.

Sampling and analysis

Urine is collected end-of-shift in a 60 ml universal container without preservative, frozen and shipped to a UKAS-accredited laboratory. Analysis uses acid hydrolysis to release the diamine from haemoglobin and protein adducts, followed by LC-MS/MS quantification. HSE BMGV for MDA is 1 µmol/mol creatinine; for TDA, 1 µmol/mol creatinine (sum of 2,4 and 2,6 isomers).

Acting on results

Results above the BMGV initiate review of spray booth LEV, supplied-air RPE fit and integrity, dermal gloves (nitrile or laminate, not latex), and curing-time work practice. Trending across campaigns identifies LEV degradation before individuals reach the BMGV.