Case Study: Isocyanate Biological Monitoring

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Anonymised case study describing the design and outcome of an MDI biological monitoring programme at a UK industrial coatings manufacturer running two PU spray lines and a small adhesives kitting area.

Workplace scenario

A medium-sized industrial coatings manufacturer operating two MDI-based PU spray lines (architectural coatings) and a kitting area where MDI prepolymer is decanted into adhesive cartridges. Combined workforce of 28 across direct production and maintenance.

Exposure concern

Routine air monitoring showed all 8-hour TWAs below the WEL for NCO. However, two reported episodes of mild respiratory irritation in line operators, plus a recent HSE inspection focus on isocyanates, prompted a switch from air-only to combined air + biological monitoring.

Monitoring approach and sampling strategy

Urinary MDA end-of-shift, twice per year, all 14 line operators and 4 kitting area workers. Maintenance fitters sampled separately around scheduled line cleans. SEGs defined by line and shift. Samples collected within 30 minutes of shift end, frozen for transport, LC-MS/MS analysis after acid hydrolysis at a UKAS-accredited laboratory. HSE BMGV of 1 µmol MDA/mol creatinine adopted as the cohort review trigger.

Interpretation themes

Line 1 (newer enclosed booth, downdraft LEV) cohort GM at ~25% of BMGV. Line 2 (older booth, sidedraft LEV) cohort GM at ~70% of BMGV — review trigger crossed. Kitting area: two individuals above BMGV, traced to nitrile glove permeation during repeated decanting.

Control improvements and lessons learned

Line 2 LEV refurbishment, supplied-air visor fit-test refresh and a switch from nitrile to laminate gloves in the kitting area. Six-month follow-up showed line 2 GM dropping to <30% of BMGV and all kitting area workers below BMGV. Key lesson: dermal uptake during decanting was invisible to air monitoring and would not have been identified without biomonitoring.