Wildfire Smoke Worker Protection: What the AQI at the Worksite Reveals

10.09.2026

Wildfire smoke worker protection is written into law with actual numbers in only one part of the world. Two American state regulators name an air quality index value at which employer duties begin. Everywhere else the obligation exists but the number does not. Australian, British and German employers are told to assess the risk and act reasonably, with no threshold to assess against.

That gap matters, because the pollutant ignores it. The fine particulate fraction in wildfire smoke behaves the same way in Brandenburg as it does in northern California. What differs is whether anyone is obliged to measure it, and whether the value used to make the decision actually reflects the location where the work is being done.

Wildfire smoke worker protection across four regulatory regions

Only the United States sets a legal air quality index threshold for outdoor work during smoke events. Australia, the United Kingdom and the German-speaking countries impose a general duty to assess and control the risk without naming a trigger value.

The four regions do not even share a scale:

• United States: the EPA air quality index, running from 0 to 500 across six categories
• United Kingdom: the Daily Air Quality Index, a 1 to 10 scale grouped into four bands
• European Union: named bands from Good to Extremely Poor, calculated hourly
• Australia: no numeric index at all. New South Wales replaced it with five Air Quality Categories in November 2020, following the review that came out of the 2019 to 2020 fire season

The practical consequence is that one concentration carries four different labels. A PM2.5 level of 55.5 micrograms per cubic metre reads as AQI 151 in the United States, which is the exact point at which Californian duties begin. The same air is "Very poor" under the European index and band 7 of 10 in the United Kingdom. New South Wales offers no comparable number at all: its five categories are set against hourly cut-offs rather than an index. A safety team operating across borders is reading four instruments that do not agree on what to call the same air.

The California threshold model in practice

California requires employers to act once the current AQI for PM2.5 reaches 151, and to require respirator use above 500. The rule, Title 8 section 5141.1, applies wherever exposure to wildfire smoke is reasonably anticipated.

At what AQI must outdoor work change?

At 151 the duties begin. Employers must communicate the hazard, train workers, apply engineering and administrative controls where feasible, and supply NIOSH-approved respirators for voluntary use. Above 500 respirator use stops being voluntary. Several exemptions apply, including enclosed buildings with filtered air and total exposure of one hour or less per shift.

The regulation permits three equally valid ways of establishing that number:

1. Check a public source such as EPA AirNow, the California Air Resources Board or the local air district
2. Obtain the figure directly from an agency
3. Measure PM2.5 at the worksite and convert it using Appendix A of the regulation

The first route deserves more credit than it usually receives. Regulatory monitoring networks are operated to documented quality assurance procedures, use federal reference or equivalent methods, and are subject to audit. A single site instrument, however good, carries none of that institutional backing. For establishing a legally defensible figure, the public network remains the primary route, and section 5141.1 treats it as sufficient on its own.

The Oregon three-stage escalation model

Oregon triggers lower than California and escalates in three stages. Duties begin at 35.5 micrograms per cubic metre (AQI 101), with further.

Oregon's design differs in an instructive way. The rule is anchored to PM2.5 concentrations rather than to index values, which is why its published AQI figures look unusual. Oregon OSHA has confirmed that the EPA's 2024 revision left those concentrations untouched: only the index numbers printed alongside them moved, which is why the rule text still names AQI 251 and 501 where current guidance names 277 and 849.

1. First stage: employers assess air quality, train workers, establish two way communication, apply controls and provide respirators for voluntary use
2. Second stage: respirator use becomes mandatory under a dedicated programme
3. Third stage: the full respiratory protection standard comes into force

Oregon also states the direct measurement option more plainly than California does. Employers may choose to measure workplace ambient PM2.5 themselves using a calibrated measuring device, following the manufacturer's instructions.

Consequences of an unmeasured smoke incident

Outside the United States, employers carry a duty to assess smoke exposure without any numerical threshold to assess against. The health evidence is not in doubt; only the trigger is missing.

Safe Work Australia requires businesses to identify, assess and control risks from air pollution including bushfire smoke, and to monitor smoke levels.  It names no AQI or PM2.5 figure anywhere. SafeWork NSW directs employers to monitor via public alerts and to confirm that visibility and air quality have improved before outdoor work resumes. The emphasis falls on dynamic risk assessment rather than on trigger points.

The United Kingdom has no equivalent standard at all, during what has become its worst wildfire year on record. Fire services in England and Wales attended 458 wildfire incidents in July 2026, the busiest month ever recorded, followed by 185 in the first ten days of August. By 10 August the year to date stood at 966 incidents, ahead of the same point in the two busiest years previously recorded. Guidance from UKHSA is addressed to the general public. A worker's formal recourse is generic, resting on dynamic risk assessment and, in extremity, section 44 of the Employment Rights Act 1996.

Germany, Austria and Switzerland have no wildfire smoke rule for outdoor workplaces either. The obligation runs through the general Gefährdungsbeurteilung, supported by the general dust limit value under TRGS 900 and related occupational limits that were never designed for smoke drifting in from a fire fifty kilometres away.

The pollutant itself is well characterised. The US EPA identifies PM2.5 as the principal pollutant of concern in wildfire smoke, supported by extensive evidence linking short term exposure to respiratory irritation, aggravated heart failure and increased emergency department attendance. As Dorota Jarosinska of WHO Europe put it in July 2026, "If you can smell smoke, it's already in your breathing air."

Distance Between Monitoring Station and Worksite

Regulatory monitoring stations are sited to characterise  population exposure across an urban area, not conditions at a particular worksite. The value they publish is an accurate description of the location where the instrument stands.

That distinction is easy to state and easy to underestimate. Networks are designed for spatial coverage of populations, which means station density reflects where people live rather than where crews work. Terrain compounds the effect, because smoke pools in valleys and drains overnight in ways that a single reading several kilometres away cannot capture.

How far away is the nearest monitoring station?

For an urban depot, often a few kilometres. For a quarry, a linear construction project, a forestry block or a rural utility crew, the nearest station may be tens of kilometres distant and on the other side of a ridge. The published figure remains the correct regulatory reference. It simply may not describe the air the crew is breathing at eleven in the morning.

The gap runs in both directions,  which is the part usually missed. A site can be dirtier than the regional figure suggests, and it can also be cleaner. Under section 5141.1 an employer who demonstrates by measurement that PM2.5 at the worksite does not correspond to an AQI of 151 or greater is exempt from the standard.

Two valid methods, two different numbers

The EPA revised its PM2.5 breakpoints on 6 May 2024, compressing the upper end of the scale. The conversion table in Appendix A of section 5141.1, as published, still uses the earlier values.

Which conversion applies when measuring on site?

The regulation's own appendix applies to the measurement route. That produces a divergence at higher concentrations. Under the current EPA breakpoints the "Unhealthy" band spans from 55.5 to 125.4 µg/m3, while Appendix A retains 55.5 to 150.4 µg/m3. The 151trigger itself is identical under both, which is reassuring for the threshold that matters most. Higher up they part company. Air at 200 µg/m3 reads close to 275 on a public source and roughly 250 under Appendix A.

A second mismatch sits alongside the scale question. The public AQI for PM2.5 is derived from a 24-hour average, in AirNow's case a weighted running version of it, while a direct-reading instrument reports over a minute or an hour. Converting a short-term reading through Appendix A therefore compares two different reference periods, and in a fast-moving plume the short-term figure moves first and further.
Safety teams working from an internal rule of thumb written before May 2024 should check which scale it was built on. The number has moved even though the smoke has not.

Regulatory requirements for on-site monitors

An instrument used to establish the AQI under section 5141.1 must meet defined criteria. These are set out in Appendix A and are stricter than most direct reading monitors are marketed against:

• Measure particles with an aerodynamic diameter of 0.3 micrometres or less up to and including 2.5 micrometres
• Not underestimate exposure, or account for documented measurement error so that underestimation does not occur
• Be calibrated, maintained and used in accordance with the manufacturer's instructions
• Be operated under supervisory personnel with the training or experience needed to interpret the results correctly

Two distinctions follow. A device corrected against a customer's own gravimetric reference is not thereby a calibrated instrument, and gravimetric sampling remains the reference method for compliance assessment. Readers evaluating that route will find the mechanics in the note on correction factors for optical measurement. And an instrument worn on the body samples the breathing zone, whereas the regulation asks for ambient air concentration. A body worn reading taken beside a dust generating task will sit above true ambient.

Continuous measurement at the workplace

Dustlight calculates an air quality index from its PM2.5 measurement and displays it on the device itself. The scale is selectable between the plain US EPA index and the Cal/OSHA action thresholds under section 5141.1, which mark 151 and 500 on that same index rather than forming an index of their own , as a one minute or one hour average.

The mechanism is straightforward. The instrument a worker already carries for occupational dust exposure derives an index value from the same measurement, at the location where the work is being done. The averaging period matters here. One hour smooths short fluctuations and matches how public indices are reported, while the one minute setting on Dustlight registers smoke arriving over a ridge as it happens rather than after the average has smoothed it out . A site manager weighing whether outdoor work continues sees a figure from the site itself. Where conditions deteriorate quickly, the Dustlight display warns the wearer at the point of exposure rather than at the next shift briefing.

That awareness is the function, and its boundary should be stated clearly. The Dustlight index supports operational judgement; it does not establish the regulatory figure. Determination under section 5141.1 or the Oregon rule should rest on a public source or on an instrument that satisfies Appendix A in full, and Dustlight is not offered as that instrument. The index is also available on the device only in this release, with history, trends and reporting to follow, so it cannot yet serve as documentation. It is available on every device regardless of plan.

Practical steps without a regulatory threshold

Employers outside the United States can adopt a threshold voluntarily. Nothing prevents an Australian, British or German organisation from writing a PM2.5 trigger into its own risk assessment and acting on it.

The American rules offer a tested starting point, and their underlying concentrations translate across scales even where the index numbers do not. A concentration based trigger travels better than an index value. Three elements make it workable:

1. A stated concentration at which controls change
2. A defined way of establishing that concentration
3. A route by which the value reaches the people doing the work rather than the file

The last of those is where most schemes fail. A threshold nobody sees is a threshold nobody applies. Whether the number comes from a public network or from a device worn by the crew, wildfire smoke worker protection depends on it arriving while the shift is still running.