Isocyanates — Workplace Exposure Limit Change

Isocyanates are the leading cause of occupational asthma in Australia. They are potent respiratory sensitisers — once a worker develops sensitisation, even trace exposures far below the WEL can trigger severe asthmatic reactions. Sensitisation is irreversible and typically ends the worker's career in any isocyanate-exposed occupation. Acute high-level exposure causes chemical pneumonitis with symptoms including chest tightness, coughing, wheezing, and shortness of breath. Chronic low-level exposure below the current WES can still cause sensitisation in susceptible individuals, which is the primary driver for the limit reduction. Skin contact with isocyanates can also cause sensitisation through dermal absorption, and once sensitised through the skin, subsequent inhalation exposure triggers respiratory symptoms. Hypersensitivity pneumonitis has been reported in workers with prolonged isocyanate exposure.

Personal air sampling using reagent-coated glass fibre filters (DBA or MAP reagent) or midget impingers with tryptamine reagent. Analysis by HPLC with UV detection following NIOSH Methods 5521, 5522, or 5525 depending on the isocyanate species. Real-time monitoring with direct-reading instruments can supplement filter sampling for task-based exposure assessment.