Diacetyl WEL 0.04 mg/m³ TWA / 0.07 mg/m³ STEL: what PCBUs should do before Dec 2026

Why this pair matters

Diacetyl (2,3-butanedione) is a new WEL substance: 0.04 mg/m³ (0.01 ppm) as an 8-hour TWA and 0.07 mg/m³ (0.02 ppm) as a STEL. WES remains the reference until 30 November 2026; WEL applies from 1 December 2026 once implemented. Check your WHS regulator.

Where it shows up

• Flavour compounding and food manufacture.
• Heated processing, mixer/kettle dose, clean-down and maintenance.
• Laboratory, sensory/QC, drum charge and tip.

SEG and register checklist

Name diacetyl where SDS disclose it. Map weigh/tip, mixer/kettle, packaging, clean-down, maintenance and lab SEGs, including contractors. Check LEV, heated lids, permits, emergency procedures and historical monitoring. Job titles alone are not a SEG.

Controls and monitoring

Prefer diacetyl-free or closed formulations. Enclose tip/dose, capture heated points, maintain exhaust and ducts, minimise open time and purge before breaks. Baseline both limits: full-shift personal TWA samples and STEL-capable short-term samples during tip, dose, heated work and clean-down. Agree media and low reporting limits with the lab. Odour is not quantitative exposure data. Use compatible gloves and fit-tested vapour/aerosol RPE last.

Sources

Safe Work Australia WEL changes · SWA WEL/WES changes