Phthalic anhydride’s 8-hour limit is cut from 1 ppm to 0.0003 ppm. That is the figure in Safe Work Australia’s May 2025 changes, applying from 1 December 2026 once your WHS regulator gives it effect. Until 30 November 2026 the current exposure standard still governs. The published row does not add a short-term exposure limit. Do not invent one.
This note is only about phthalic anhydride. Maleic anhydride, hexahydrophthalic anhydride and trimellitic anhydride are different substances with their own numbers. Trimellitic anhydride has its own short-term limit elsewhere. Do not paste that language onto this chemical.
A 1 ppm method cannot describe 0.0003 ppm
Sites that were “fine last year” were often comparing results to 1 ppm. That comparison does not carry forward. Three things fail together when the old plan is left in place: the register still says “resin chemicals” or “anhydrides,” the exposure groups stop at the reactor and miss weigh, charge and bag change, and the laboratory method cannot see 0.0003 ppm.
Open weigh and bag minutes usually dominate, even when the reactor looks closed for the rest of the shift. Solid powder and molten charge are not the same exposure. Record which form you run.
Where it is handled
Alkyd resin and coatings plants, plastics-additive lines, and plasticiser intermediates. The tasks that matter are weigh and charge of solid or melt, bag change and drumming, clean-down after a capture failure, small-scale lab work, and maintenance on mixers, condensers and charge chutes. Contractors who open a vessel after production has left need their own line on the map.
Questions that match this magnitude
Is phthalic anhydride named, or buried in a family heading? Do the groups include the weigh station and bag change? What would last year’s results look like beside 0.0003 ppm, not beside 1 ppm? Has the hygienist confirmed a method whose limit of quantification can support that comparison? Is extraction at the weigh point checked at the charge rate you actually use?
Permits for chute and vessel opening should treat residue as expected dust and vapour. Safety data sheets and emergency steps should name phthalic anhydride, not a generic anhydride.
What to change before you promise a survey
Cut open weigh and charge where closed charge or a reformulation is practicable, and write down the residual risk if you cannot. Enclose what remains and keep local exhaust at bag change and melt charge. Check it under production rates. Condenser, chute and vessel entry need a written sequence.
Keep bystanders out of the weigh area. Respiratory protection, where it is still needed, has to be selected for the concentration you now have to take seriously, with fit testing and a change rule. It is a poor sole control on a weigh station that can be extracted.
Talk to the occupational-hygiene provider before anyone is mobilised. At this concentration the survey fails first on the method, not on the roster. Only commission baseline sampling against 0.0003 ppm when the laboratory can defend the comparison. Train operators on phthalic anhydride by name, and keep the other anhydrides in their own sessions.
Do not claim your state has already adopted the new limit unless the regulator has said so in writing.
FAQ
What are the numbers? Exposure standard 1 ppm, 8-hour average. New limit 0.0003 ppm, 8-hour average. The change is a reduction, not a new listing.
Is there a short-term limit? Not on this row. Do not borrow one from trimellitic anhydride.
When does 0.0003 ppm apply? Plan on the current standard until 30 November 2026, and the new limit from 1 December 2026 once it is in force. Confirm that with your WHS regulator.
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
If phthalic anhydride is weighed, charged or bagged on your site, book a consult to lock the register name, the exposure groups and a monitoring plan built for 0.0003 ppm.
Book a consult: anitechgroup.com · sales@anitechgroup.com
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