The incoming 8-hour limit for phthalic anhydride is 0.0003 ppm. The exposure standard it replaces is 1 ppm. Exposure standards remain the compliance reference until 30 November 2026. From 1 December 2026 the new limit applies once the WHS regulator gives it effect. The published change has no short-term exposure limit. Do not add one.
A method whose quantification limit sits at or above 0.0003 ppm cannot support a compliance claim at the new limit. That is the first question for the laboratory, before a pump is booked. State the laboratory’s actual detection and quantification limits in the plan. Do not invent them in the abstract.
Do not survey maleic anhydride, hexahydrophthalic anhydride or trimellitic anhydride under this comparator. Do not copy trimellitic anhydride’s short-term language into a phthalic report. If older data were planned against 1 ppm, show the client the gap to 0.0003 ppm. Do not imply the two figures are continuous.
Tasks that have to be on the sampled day
Weigh and charge, as powder or as melt, usually set the result. Bag change can dominate even when the reactor is closed for hours. Manual assist at the reactor, clean-down, vessel entry, and the QC bench are separate if the people and the open time differ. After-hours contractors need their own line when they open a chute the day shift does not.
Agree the groups from those tasks. Sample on a day when weigh or charge actually happens. Record the form (solid or melt), charge mass, whether local exhaust was on, open minutes, and what respiratory protection was worn.
Task samples during weigh and charge are for control diagnosis. Time-weight them into the shift average and state the assumption for unsampled hours. Static samples at the weigh point are capture checks. Label them as such.
Interpretation
In the planning window, compare averages to 0.0003 ppm only where the quantification limit makes that comparison meaningful. Also show how far the old 1 ppm assumption sits from the new figure, so nobody treats last year’s “pass” as this year’s margin.
From 1 December 2026, once in force, 0.0003 ppm is a limit not to be exceeded for people at the workplace. A non-detect is only reassuring when the detection limit is a meaningful fraction of 0.0003 ppm.
Keep phthalic anhydride in its own results table.
Report hygiene
Quote the numbers exactly: 1 ppm down to 0.0003 ppm, 8-hour averages, no short-term limit on this row. Field blanks and pump records need to be complete at this magnitude. Recommendations should start with enclosure and extraction at weigh and charge. Respiratory protection is not the first recommendation.
Before mobilisation, confirm four things with the client: the limit text, the laboratory quantification limit against 0.0003 ppm, that weigh or charge will occur on the days you attend, and that other anhydrides will not be rolled into the summary.
Sources
- Safe Work Australia, *Changes to Workplace Exposure Limits – May 2025*: https://www.safeworkaustralia.gov.au/sites/default/files/2025-05/changes_to_workplace_exposure_limits_-_may_2025.pdf
- Safe Work Australia, changes between exposure standards and exposure limits: https://www.safeworkaustralia.gov.au/safety-topic/managing-health-and-safety/workplace-exposure-limits-airborne-contaminants/changes-between-wes-and-wel
Next step
Occ Hygiene can design a weigh-and-charge survey against 0.0003 ppm once the laboratory method can support that comparison.
