Wildfire Smoke and Outdoor Work

Why this matters

Wildfire smoke now reaches shops that are a thousand miles from any fire. A roofing crew in the upper Midwest can spend a day under the same air quality as a crew beside a California fire line, and in three Western states that day triggers a legal duty while in most others it triggers nothing on paper. The health effect does not care which state you are in. The particles go deep into the lungs, the crew doing the hardest work breathes the most of them, and the protective moves are mostly scheduling decisions made before the truck leaves. The failure is checking the sky instead of the number.

This card explains what the number means, what the main state rules require, and how the federal layer sits underneath them. The daily go, adjust or stop decision is its own procedure. See related: The Smoke Day Work Decision SOP.

What is in the smoke, and why PM2.5 is the number

Smoke is a mix of gases and particles, and at any distance from the fire the particles do most of the harm. PM2.5 means particles 2.5 micrometers across or smaller, roughly a thirtieth of the width of a human hair. They are small enough to get past the nose and throat into the deep lung, and the finest reach the bloodstream. Short-term effects are coughing, burning eyes, a scratchy throat, headache, wheezing and chest tightness. For people with asthma, COPD or heart disease, smoke days bring attacks, emergency visits and, for some, heart events.

The gases, chiefly carbon monoxide, matter mainly close to an active fire. Far from it, the smoke you can see and smell is a PM2.5 problem, which is why every rule discussed here is written around PM2.5 and not around visibility. Visibility is a poor guide anyway: a hazy day can carry modest PM2.5 and a clear-looking morning can carry a high reading under an inversion.

Reading the Air Quality Index for particles

EPA's Air Quality Index converts the PM2.5 concentration into a 0 to 500 scale with fixed categories:

Three points about the number itself:

• Use the current PM2.5 reading, not the daily forecast or the ozone index. Smoke can swing a reading by a whole category in an hour. EPA's AirNow and its Fire and Smoke Map report a current hourly value built to respond to fast changes, and the state rules below are written against the current PM2.5 AQI.
• The concentration behind a given AQI number moved in 2024. EPA revised the PM2.5 breakpoints that year, so the micrograms per cubic meter that produce an AQI of 151 or 201 are not what they were when some state rules were drafted. The category numbers are unchanged. This is current as of 2026; check how your state's rule now defines its trigger.
• A low-cost sensor near the job can read differently from the nearest official monitor. EPA's smoke map shows corrected sensor data alongside monitors, which helps where the nearest monitor is far away. If a state rule applies to you, it names which readings count.

The legal layers: federal floor, state rules on top

This section describes the rules as written, not how they apply to your operation. It is not legal advice.

Federal. There is no OSHA standard for wildfire smoke. The federal layer that does reach a smoke day is the respiratory protection standard, 29 CFR 1910.134, and it turns on whether respirator use is voluntary or required. If your shop provides N95s and leaves wearing them up to the worker, the standard asks only that you give each user the information in its Appendix D. If your shop requires a respirator to be worn, the full program applies: a written program, medical evaluation, fit testing and training. Requiring masks without that program is the most common way a well-meaning shop ends up out of compliance.

California has the most detailed rule, 8 CCR 5141.1, Protection from Wildfire Smoke. It applies when the current PM2.5 AQI is 151 or higher and the employer can reasonably anticipate workers will be exposed. It requires checking the AQI at the start of the shift and periodically after, a way for workers to report symptoms and for the employer to communicate changes, training, and controls such as moving work into enclosed buildings or vehicles with filtered air, changing schedules, or reducing work intensity where feasible. From 151 to 500 the employer must provide N95s for voluntary use. Above 500, respirator use is required under the state's full respiratory program. It exempts work in enclosed buildings and vehicles with filtered air and windows closed, and workers exposed for a total of one hour or less in the shift.

Oregon has a permanent rule, OAR 437-002-1081, that begins at an AQI of 101, lower than California's, with respirator duties that step up as the AQI climbs. Washington has a permanent rule, WAC 296-820, whose first planning and training duties begin lower still, in the moderate band, also stepping up at higher readings. Both differ from California in their triggers and steps, so read the current text for the state you work in rather than carrying California's numbers across.

Everywhere else, as of 2026, no state-specific smoke rule applies to most private employers, and the federal respiratory standard above is the layer that governs what you hand a worker. Check your state's OSHA plan, because state plans can adopt rules mid-season. Where the question becomes whether your shop must stop work, pay for idle time or require respirators, that is the point to call your state OSHA consultation program or an employment attorney, and walk in with your AQI readings and the hours each worker spent outdoors.

Who breathes the most

The dose a worker takes in is the concentration times the volume of air they breathe. A person at rest moves roughly 6 to 8 liters of air a minute. Heavy labor, tearing off shingles, digging, hauling sod, pushes that to 40 liters a minute or more. So at the same AQI, a roofer doing tear-off inhales several times the particles of a tech reading a thermostat. That is why the protective moves rank in this order: cut the heavy outdoor work first, then shorten exposure time, then add respirators.

Respirators work only when they seal. A NIOSH-approved N95 filters at least 95 percent of particles of the hardest size to catch, and the approval is printed on the mask. Paper dust masks, surgical masks and cloth face coverings do not provide that protection. Facial hair under the seal defeats any tight-fitting respirator, which is not a matter of opinion but of air taking the easy path. An N95 does nothing for gases. And it adds breathing resistance, which matters on a hot day.

Indoors is not automatically clean. Homes leak, and a house with windows open and no filtration can read close to outdoors. An attic or a vented crawlspace exchanges air with the outside by design, so moving a job "inside" into the attic moves it nowhere. A closed home running a good filter, or a vehicle with windows up and the cabin air on recirculate, is the real refuge.

Worked example: one smoke day, three shops

The same morning, 8:00 a.m., three four-person roofing crews each read a current PM2.5 AQI of 165 at their jobs. All three plan an eight-hour tear-off.

The California crew. At 165 the state rule applies, because the reading is at or above 151 and the crew will be outdoors. The employer must have trained the crew, must keep checking the AQI through the shift, must provide N95s for voluntary use, and must use feasible controls. The one-hour exemption does not apply to an eight-hour tear-off. The shop moves the tear-off to another day and sends two of the four to service calls in closed, filtered homes, while the other two finish a short gutter job in about 3 hours with N95s offered. Outdoor crew-hours fall from 32 (4 workers times 8 hours) to 6 (2 workers times 3 hours), and the rule still applies to those two, because 3 hours is past the one-hour exemption.

The Oregon crew. At 165 the reading is well past Oregon's 101 trigger, so its rule applies with its own assessment, training and respirator steps. The shop's choices look like California's, but the duties come from Oregon's text, not California's.

The upper Midwest crew. No state smoke rule applies. The only legal layer is the federal respiratory standard, and only if the shop hands out respirators. The owner decides to offer N95s for voluntary use and gives each worker the Appendix D sheet. Two of the four have full beards, so for them the mask offers little protection. One has asthma. The owner reschedules the tear-off anyway, for the same reason the California rule exists: the crew doing the heaviest work at an AQI of 165 is breathing several times the dose of anyone else, and two of the four cannot get a seal.

What the comparison teaches. The decision was nearly the same in all three shops. What differed was whether the shop was obliged to make it, whether it had to document it, and which text set the steps. A Midwest owner who reads "no rule here" as "no risk here" is making a legal observation and a medical mistake at the same time.

What changes the answer. A reading above 500 in California makes respirator use mandatory under the full state program, so a crew without fit testing simply cannot do that work there. A job near an active fire adds carbon monoxide and evacuation orders, which no mask addresses; leave when officials say leave. Cleaning up ash after a fire is a different exposure, with caustic wet ash and possible metals, and belongs to the restoration side, not this card. And a smoke day that is also a hot day stacks two hazards, because the respirator raises breathing effort while the heat raises everything else. See related: Heat Stress + Jobsite Hydration Reference.

Symptoms that change the plan

Any worker who develops wheezing, chest tightness, shortness of breath beyond what the work explains, or eye and throat irritation that worsens, moves indoors to filtered air and stops outdoor work for the day. Chest pain, an irregular or racing heartbeat, confusion or severe shortness of breath is a 911 call, not a rest break. A worker with asthma should have their rescue inhaler on them, not in the truck, on every smoke day.

References

• EPA, AirNow and the Fire and Smoke Map; Wildfire Smoke: A Guide for Public Health Officials
• 29 CFR 1910.134, respiratory protection, including Appendix D for voluntary use
• California Code of Regulations, Title 8, Section 5141.1, Protection from Wildfire Smoke
• Oregon OSHA, OAR 437-002-1081; Washington L&I, WAC 296-820
• See related: The Smoke Day Work Decision SOP