The Definition of Wildfire Smoke Exposure

Definition of Wildfire Smoke Exposure

Wildfire smoke exposure refers to workers breathing smoke from wildfires while on the job. Wildfire smoke contains gases such as carbon monoxide and a mixture of chemicals, but the main health concern is fine particulate matter known as PM2.5, particles 2.5 micrometers in diameter or smaller. These particles can travel deep into the lungs and enter the bloodstream.

Smoke can travel hundreds or thousands of miles from a fire, so workers far from any flames can be affected. Outdoor workers in construction, agriculture, landscaping, utilities, delivery and emergency services face the highest exposure, but indoor workers can also be affected when smoke enters buildings.

Health Effects

• Eye, nose and throat irritation, coughing and headaches.
• Shortness of breath and worsening of asthma and chronic obstructive pulmonary disease (COPD).
• Increased risk of heart attacks, irregular heartbeat and strokes in people with heart disease.
• Greater risk for older workers, pregnant workers and those with existing heart or lung conditions.
• Combined effects with heat, since smoke events often occur during hot weather and both raise strain on the heart. See heat stress.

Measuring Exposure: The Air Quality Index

Employers usually rely on the U.S. Air Quality Index (AQI) for PM2.5, available from AirNow.gov, state agencies and many weather apps. AQI categories range from Good (0 to 50) to Hazardous (301 and above). Readings from local monitors or portable sensors can help assess conditions at a specific worksite.

Regulations

Federal OSHA has no specific wildfire smoke standard. Employers are still expected to protect workers from recognized hazards under the General Duty Clause, and respirators used must meet the respiratory protection standard, 29 CFR 1910.134.

Several western states have their own rules:

• California: Title 8, Section 5141.1, applies when the current AQI for PM2.5 is 151 or higher and employers can reasonably expect workers to be exposed. Employers must communicate with workers, train them, reduce exposure where feasible and provide N95 respirators for voluntary use. When the AQI exceeds 500, respirator use is required under a full respiratory protection program.
• Oregon and Washington: both have permanent wildfire smoke rules that begin at an AQI of 101, with increasing requirements as conditions worsen.

Controlling Wildfire Smoke Exposure

• Monitor: check the AQI before and during shifts and set action levels.
• Relocate or reschedule: move work indoors or to areas with better air, or delay nonessential outdoor work.
• Filter indoor air: keep windows and doors closed and use HVAC filters rated MERV 13 or higher, or portable HEPA air cleaners.
• Use enclosed vehicles and equipment: with filtered air and recirculation on.
• Reduce exertion: lower work rates and add rest breaks to reduce breathing rates.
• Provide respirators: NIOSH-approved filtering facepieces such as N95s, with training on proper fit and use. Surgical and cloth masks do not provide adequate protection.
• Communicate: tell workers about current conditions, controls and how to report symptoms.

Example of Wildfire Smoke Exposure

A landscaping company in Northern California had crews working outdoors when smoke from a distant wildfire pushed the PM2.5 AQI to 180. Under the company's wildfire smoke plan, supervisors checked AirNow every two hours and notified crews by text when the AQI crossed 151.

The company moved crews from heavy work such as tree removal to lighter maintenance tasks, shortened outdoor shifts and provided N95 respirators with training on fit. Workers with asthma were reassigned to indoor tasks at the yard, where portable HEPA air cleaners ran in the break room. When the AQI rose above 300 for a day, outdoor work was postponed.

Frequently Asked Questions: Wildfire Smoke Exposure

Do surgical masks protect against wildfire smoke?

No. Surgical and cloth masks do not seal to the face or filter fine particles well. NIOSH-approved respirators such as N95s, worn correctly, provide much better protection.

What AQI level is unsafe for outdoor work?

Risk increases as the AQI rises. Sensitive workers may be affected above 100. California's rule begins at 151, and Oregon and Washington begin at 101.

Can wildfire smoke affect indoor workers?

Yes. Smoke can enter buildings through ventilation systems, doors and windows. Filtered air and sealed buildings reduce indoor exposure.