If you work with phosphine in grain storage or handling, the main change is simple: Australia is moving to much lower workplace exposure limits for phosphine from 1 December 2026. The changes apply to the amount of phosphine gas workers can be exposed to in the air. They do not directly change the fumigation dose used to treat grain, but they may require changes to monitoring, ventilation, work procedures and detector settings.
The new phosphine limits are:
- 8-hour time-weighted average (TWA): reduced from 0.3 ppm to 0.05 ppm.
- Short-term limit: the current 1 ppm STEL will be replaced by a 0.15 ppm peak limit.
Safe Work Australia currently states that the new Workplace Exposure Limits, or WEL, will apply from 1 December 2026, after implementation in Commonwealth, state and territory WHS laws. Until 30 November 2026, businesses must continue complying with the current Workplace Exposure Standards, or WES. Read the Safe Work Australia transition information.
What are the new Australian phosphine exposure limits for grain storage?
Two things are changing. First, the name is changing from Workplace Exposure Standards (WES) to Workplace Exposure Limits (WEL). Second, the actual exposure values for a number of airborne contaminants are changing. Phosphine is one of the substances with substantially lower limits.
For phosphine, the comparison is:
- Current limit until 30 November 2026: 0.3 ppm TWA and 1 ppm STEL.
- New limit from 1 December 2026: 0.05 ppm TWA and 0.15 ppm peak limit.
The official WEL list shows phosphine, CAS number 7803-51-2, with a TWA of 0.05 ppm and a peak limit of 0.15 ppm. View the official WEL list.
Why is Australia changing from WES to WEL for phosphine gas?
The word “standard” can sound like a target or guideline. The term “limit” is intended to make it clearer that the value must not be exceeded. The change also aligns Australian terminology with terms used internationally. The new list follows a review of the exposure standards using more recent health evidence.
When do the new phosphine limits start for the Australian grain industry?
The scheduled start date is 1 December 2026. The transition period ends on 30 November 2026. Because WHS requirements are implemented through individual jurisdictions, businesses should also check the position of their state, territory or Commonwealth WHS regulator before the start date.
Who in grain storage, handling and fumigation is affected by the new phosphine limits?
The changes are relevant to any workplace where workers may breathe phosphine gas. In the grain industry, this may include:
- grain growers and on-farm storage operators
- fumigators and pest-control contractors
- silo, bunker and warehouse operators
- grain receival, handling and processing facilities
- maintenance workers, samplers, drivers and contractors entering areas where phosphine may be present
Do the new phosphine WEL rules change grain fumigation rates?
No. The WEL change is about worker exposure to phosphine in workplace air. It does not, by itself, ban phosphine or set the fumigation concentration inside sealed grain storage. However, businesses may need to change the way fumigation areas are isolated, ventilated, tested and cleared before people enter or work nearby.
What does the 0.05 ppm phosphine TWA mean for grain workers?
TWA means 8-hour time-weighted average. It is the worker’s average exposure over an eight-hour working day, based on a 40-hour week. From 1 December 2026, the average phosphine exposure over that period must not be above 0.05 ppm.
The 0.05 ppm value is not simply an instantaneous alarm point. A brief reading above 0.05 ppm does not automatically mean the eight-hour TWA has been exceeded, but it contributes to the worker’s total exposure. Longer shifts, longer working weeks or short recovery periods between shifts may require a lower adjusted TWA, calculated with qualified advice.
What does the 0.15 ppm phosphine peak limit mean during grain fumigation?
The peak limit is different from a TWA. It is the maximum concentration measured over the shortest practical period, not exceeding 15 minutes. Exposure above 0.15 ppm is not permitted at any time under the new limit, even when the worker’s average exposure for the day would remain below 0.05 ppm.
This is also different from the current 1 ppm STEL, which is a 15-minute time-weighted average. Under the new WEL, phosphine has a peak limit rather than a STEL. Safe Work Australia explains TWA, STEL and peak limits in the WEL document.
Why do lower phosphine exposure limits matter for grain storage and handling sites?
The new TWA is one-sixth of the current 0.3 ppm value, and the new peak limit is much lower than the current 1 ppm STEL. This means monitoring equipment and work practices designed around the old values may not be suitable for the new limits.
The practical questions are whether a detector can reliably measure at low enough concentrations, whether short releases are being captured, and whether recorded data can be used to understand exposure across a shift. Grain Trade Australia, GRDC, the National Working Party on Grain Protection and other industry participants have been working on implementation issues for the grain supply chain. See Grain Trade Australia’s phosphine update.
How should grain businesses prepare for the 2026 phosphine WEL changes?
- Identify where phosphine may be released, including fumigation points, seals, vents, hatches, grain discharge areas, work platforms, enclosed spaces and low-lying areas.
- List the workers and contractors who may be exposed, including people who do not directly carry out the fumigation.
- Check whether existing detectors can reliably measure below 0.05 ppm and respond appropriately around 0.15 ppm.
- Begin monitoring current work so the business understands normal readings, short peaks and higher-risk tasks before the new limits apply.
- Review isolation, ventilation, entry, clearance, maintenance and emergency procedures using the hierarchy of controls.
- Review training, maintenance records, calibration procedures and exposure records.
- Use a competent occupational hygienist where specialist exposure assessment, sampling strategy or shift calculations are required.
- Confirm the legal implementation date and requirements with the relevant WHS regulator in your jurisdiction.
Can your current grain storage phosphine detector measure the new limits?
Possibly, but the instrument must be checked. A detector that was selected only to warn around the old 0.3 ppm TWA or 1 ppm STEL may not have the sensitivity, resolution, response time or data functions needed for the new values.
A review should confirm:
- the phosphine measurement range and displayed resolution
- reliable performance at and below 0.05 ppm
- response and recovery time around the 0.15 ppm peak limit
- whether the instrument measures continuously or only during spot checks
- whether data logging is available for reviewing exposure over time
- the effect of sampling line length, flow, temperature, humidity and interfering gases
- calibration, response-test and sensor-replacement requirements
How to set up Interscan phosphine gas detectors for grain storage and fumigation
Interscan offers fixed and portable gas-detection systems with active sampling, continuous measurement, alarm functions and data logging, depending on the model and sensor configuration. The correct phosphine range must be selected for the site and the new low-level limits. View Interscan gas detector options.
A practical setup review should cover the following points:
- Measurement capability: select a phosphine sensor and range that can reliably measure below 0.05 ppm. Do not rely on the display resolution alone as proof of measurement performance.
- TWA monitoring: treat 0.05 ppm as an eight-hour average, not as a simple instantaneous compliance alarm. Continuous logged data or a suitable exposure-monitoring method is needed to assess exposure over a shift.
- Early warning: use a site-specific low warning level that gives workers time to respond before exposure approaches the applicable limits. The warning point should be set through the site risk assessment.
- Peak alarm: configure the high alarm at or below the 0.15 ppm peak limit, allowing for instrument accuracy and response time and following advice from a competent specialist.
- Sampling locations: place fixed sampling points and use portable sampling based on likely release points, worker breathing zones, ventilation movement and site layout.
- Data records: retain time-stamped readings so short releases, repeated events and shift exposure patterns can be reviewed.
Interscan AccuSafe fixed-point systems provide active continuous sampling, low-level gas sensing, alarms and data logging. Learn more about Interscan data logging.
Interscan can review an existing phosphine detector or help specify a new system based on the required range, resolution, sampling arrangement, alarm logic and data records. Not every phosphine detector or sensor configuration will automatically be suitable for the new Australian WEL, so the equipment should be assessed before alarm values are changed. Request an Interscan system review or quote.
Takeaway for Australian grain businesses using phosphine
From 1 December 2026, the Australian phosphine workplace exposure limits are scheduled to fall to 0.05 ppm as an eight-hour TWA and 0.15 ppm as a peak limit. Businesses that use phosphine should not wait until the change takes effect. The immediate task is to confirm where exposure occurs, whether current controls are effective and whether existing detectors can reliably measure and record the lower concentrations.
Phosphine WEL sources and grain industry guidance
1. Safe Work Australia: Workplace Exposure Limits – airborne contaminants
https://www.safeworkaustralia.gov.au/safety-topic/managing-health-and-safety/workplace-exposure-limits-airborne-contaminants
2. Safe Work Australia: New WEL to apply from 1 December 2026
https://www.safeworkaustralia.gov.au/media-centre/news/new-workplace-exposure-limits-wel-apply-1-december-2026
3. Safe Work Australia: Workplace exposure limits for airborne contaminants, November 2025
https://www.safeworkaustralia.gov.au/sites/default/files/2025-11/workplace-exposure-limits-amended-november_2025.pdf
4. Safe Work Australia: Changes between the WES and WEL
https://www.safeworkaustralia.gov.au/safety-topic/managing-health-and-safety/workplace-exposure-limits-airborne-contaminants/changes-between-wes-and-wel
5. Grain Trade Australia: Safe Work Australia phosphine information
https://graintrade.org.au/nwpgp/safework-australia-phosphine/
6. Workplace Health and Safety Queensland: Phosphine gas
https://www.worksafe.qld.gov.au/safety-and-prevention/hazards/hazardous-exposures/phosphine-gas
7. Interscan: AccuSafe fixed-point gas detection
https://gasdetection.com/products/accusafe/
8. Interscan: Gas detector products
https://gasdetection.com/products/
9. Interscan: Data logging
https://gasdetection.com/benefits/data-logging/
10. Interscan: Request a quote
https://gasdetection.com/contact/request-a-quote/
This article provides general information and does not replace legal advice, occupational-hygiene advice, product instructions or guidance from the relevant WHS regulator.
