Peracetic acid appears on Safe Work Australia’s WEL list as a new airborne contaminant with a peak limitation of 0.4 ppm (1.24 mg/m³). The listing has no 8-hour TWA or STEL, and there was no previous WES. The WEL list defines a peak limitation as “the maximum or peak concentration of an airborne contaminant measured over the shortest time possible, and not exceeding 15 minutes”, and adds that “Exposure above the peak limitation is not allowed at any time.”
Until 30 November 2026, the WES list remains the compliance reference, and it has no entry for peracetic acid. From 1 December 2026 the WEL applies, once the WHS regulator in your jurisdiction gives it effect. Victoria sits outside the model WHS laws, so check with WorkSafe Victoria for Victorian sites.
What you are measuring
Peracetic acid is a reactive oxidising sanitiser. Airborne exposure is mostly vapour, with mist or aerosol possible during spraying and fogging. The monitoring plan should state:
- Target analyte and reporting basis. Report in ppm, with mg/m³ alongside; SWA treats the ppm figure as exact and the mg/m³ figure as a guide.
- That the WEL comparator is a peak limitation of 0.4 ppm, judged on the maximum concentration over the shortest analytically practicable period, never longer than 15 minutes.
- That an 8-hour TWA result cannot show compliance with a peak limitation, and won’t be used for that purpose.
- Which tasks are expected to produce the highest concentrations, and how each sample will be timed to catch them.
Site patterns that drive strategy
- CIP make-up and dosing: IBC connection, day-tank charge, titration sampling
- Filler and equipment spray: brief but close to the source, and easy to miss if you only sample sealed automated CIP
- Fogging and room sanitation: often night shift or contractors
- Pharma and biotech wipe-spray programmes: smaller volumes, sometimes weaker LEV
- Maintenance: line breaks after an imperfect flush on sanitiser circuits
- Spill response: episodic SEGs that still need a plan
Reactive chemistry means media selection and sample integrity need early agreement with the laboratory. Don’t treat PAA like a stable VOC analogue without checking recovery and interferences, particularly the hydrogen peroxide and acetic acid present in most PAA blends.
SEG walkthrough
Example survey plan for a beverage site:
- SEG A: CIP and dosing operators. Short task samples at make-up, IBC coupling and open sampling of the day tank.
- SEG B: filler sanitation spray. Task-based samples at the carousel; may nest inside A if the same people do the same tasks.
- SEG C: night fog and contract cleaners, usually separate. Sample the start of each fog run and any re-entry before the room has cleared.
- SEG D: maintenance line breaks on sanitiser circuits. Sample from the moment the line opens.
- Covariates: stock vs use-dilution, spray rate, room volume, LEV on or off, temperature, RPE worn (context only).
Define “worst case” for each SEG before mobilising. Sampling between CIP cycles answers the wrong question.
Sampling strategy for a peak limitation
- Time samples to the peak. Start at the moment of opening, coupling, pouring or fogging. Typical targets are dosing, CIP make-up, decanting, opening tanks or lines, and fog start-up.
- Keep sample periods short. Use the shortest period the method can support, and never more than 15 minutes. Agree with the laboratory, in writing, the minimum sample duration that still gives a detection limit well below 0.4 ppm. If the method can’t reach that inside 15 minutes, say so in the plan, because the result won’t be able to show compliance.
- Use real-time direct-reading monitoring where a suitable instrument exists. A logging instrument shows the shape of the exposure and its true maximum within a task. Check the sensor’s cross-sensitivity to hydrogen peroxide with the supplier, and record calibration and response time.
- Personal breathing-zone samples for comparison with the limit. Static samples at make-up points are useful for LEV diagnosis but must be labelled diagnostic.
- Record task timing alongside every sample, so each result can be tied to what the worker was doing.
- Repeat across sanitation cycles and contractor shifts, enough to see whether one clean make-up was luck or design.
A full-shift sample can still be collected to describe overall exposure, but label it as context. It is not a WEL comparison for peracetic acid.
Design detail worth writing into the plan
- Breakthrough controls for when concentrations spike during open pour or fog start-up
- Storage and transport conditions that respect analyte reactivity
- Clear instruction on whether RPE is worn during sampled tasks
- Separate diagnostic static samples at make-up points for LEV performance, labelled diagnostic rather than personal
Interpretation
- Compare the maximum. The comparison is the highest breathing-zone result against 0.4 ppm. Averaging short samples together, or time-weighting them into a shift figure, hides exactly what the limit is meant to catch.
- Report sample duration with every result. A 15-minute integrated sample is itself an average over that period and can understate a spike lasting a minute or two. Direct-reading maxima help here.
- Before 1 December 2026, results are a baseline against the incoming limit. There is no current WES for peracetic acid to compare against.
- From 1 December 2026, once the WEL has effect in your jurisdiction, a breathing-zone result above 0.4 ppm means exposure went above a limit that is not allowed to be exceeded at any time.
- Non-detects: state the detection limit for that sample duration relative to 0.4 ppm. A non-detect from a method whose limit sits near 0.4 ppm tells you very little.
- Long shifts: SWA states a peak limitation cannot be adjusted for longer or shorter working days, so no shift adjustment applies.
Surface contamination and dermal risk may dominate even when air results are low. Air monitoring alone does not close the risk assessment.
Method hygiene (peer expectations)
- Cite the laboratory method ID and accreditation scope
- Avoid claiming “AS X requires …” unless verified for this analyte
- Keep field notes good enough to reconstruct the SEG logic and task timing
- Separate the compliance comparison from control-performance diagnostics
- Report peracetic acid against a peak limitation only. Don’t present a TWA or STEL comparison for it
Control hierarchy cues for recommendations
When short-term results approach 0.4 ppm:
- Eliminate or substitute: closed dosing; less fogging where efficacy allows
- Engineering: sealed make-up and LEV at spray booths; purge lines before breaking filters
- Administrative: written open-time limits; contractor inductions that name PAA
- PPE: vapour and mist RPE with change schedules, plus compatible gloves, listed last
State what evidence would show the control worked, such as repeat short-term personal samples on a representative make-up and spray day, plus a capture check at the day tank.
Does a three-minute open pour fail the WEL?
Clients ask this often, and with a peak limitation the pour is exactly where the test sits. If the maximum concentration measured over that pour is above 0.4 ppm, exposure is above the limit, whatever the shift average shows. From 1 December 2026 that is an exceedance once the WEL has effect.
The shift TWA can still describe the overall picture for the risk assessment. It cannot clear a task that peaks above 0.4 ppm.
Common failure modes
- Mobilising with generic “acid vapour” media before the laboratory confirms a method for PAA
- Full-shift sampling only, then reading the result against 0.4 ppm
- Sampling on a day with no make-up, spray or fog
- Integrated samples so long that a short spike disappears into the average
- Treating odour logs as quantitative exposure data
- Filing ppm results without stating whether they were measured or converted
- Ignoring night sanitation SEGs because production CIP is automated
FAQ (technical)
Should every report quote both 0.4 ppm and 1.24 mg/m³?
Yes, where the method supports it. Keep them paired as the published WEL expressions, and treat ppm as the exact figure.
How do we handle short fog tasks on a long shift?
Sample each fog task on its own and compare its maximum with 0.4 ppm. Don’t time-weight task results into an 8-hour figure for the WEL comparison.
Is there a TWA or STEL for peracetic acid?
No. The WEL list gives a peak limitation only, and the WES list has no entry.
What is the minimum defensible n?
Enough to characterise variability across sanitation cycles for the decision you are making. One sealed automated CIP day rarely settles a control argument near 0.4 ppm.
Sources
- Safe Work Australia, Workplace exposure limits for airborne contaminants (amended November 2025), PDF: https://www.safeworkaustralia.gov.au/sites/default/files/2025-11/workplace-exposure-limits-amended-november_2025.pdf
- Safe Work Australia, Changes to Workplace Exposure Limits (May 2025), PDF: https://www.safeworkaustralia.gov.au/sites/default/files/2025-05/changes_to_workplace_exposure_limits_-_may_2025.pdf
- Safe Work Australia, Workplace exposure standards for airborne contaminants (amended November 2025), PDF: https://www.safeworkaustralia.gov.au/sites/default/files/2025-11/workplace-exposure-standards-amended-november2025.pdf
Technical support
Need a peak monitoring plan or a report review against the incoming WEL? Start at occhygiene.com.au.
