Wildfire Smoke as an Occupational Health Hazard: Regulatory Update and Current State of the Science

Posted on Behalf of  Claire M. Hamaji, Rachel Zisook

Posted on Behalf of Claire Hamaji and Rachel Zisook.


The regular occurrence of highly destructive wildfires in California and other arid regions around the world has placed a spotlight on the health effects of wildfire smoke (Badger & Foley, 2019; CDC, 2019). In this update to our previous post on wildfire smoke as an occupational health hazard (available here), we summarize the current state of the science surrounding wildfire smoke, applicable regulations, and environmental health and safety topics that may become increasingly pertinent as wildfires continue to arise each year.

Why does wildfire smoke matter to human health?

Wildfire smoke is a complex combination of chemicals and combustion products, some of which can cause or exacerbate health conditions (USEPA et al., 2016). Particulate matter (PM) exposure is a major concern in the days and weeks following a wildfire (USEPA et al., 2016). PM less than 10 micrometers in diameter, including fine particulate matter known as PM2.5, is particularly hazardous because of its ability to penetrate deep into the lungs (USEPA, 2018). In addition to causing coughing and difficulty breathing, PM exposures can elicit heart attacks, aggravate asthma, and impair lung function, especially in people with pre-existing heart or lung conditions (USEPA, 2018). Inhalation exposure to other chemicals of concern in wildfire smoke, such as carbon monoxide and formaldehyde, can also elicit adverse health effects at sufficient doses (ATSDR, 2014; CDC, 2016).

What is being done to protect workers from wildfire smoke?

An emergency standard promulgated by Cal/OSHA in July 2019 requires that employers take measures to protect their workers from exposures to wildfire smoke (California DIR, 2019). Specifically, the standard requires that employers monitor the Air Quality Index (AQI) for PM2.5 at their worksite before each shift and periodically during each shift (Cal/OSHA, 2019). Employers may check the AQI using sources such as the USEPA AirNow website (here) and California Air Resources Board website (here), or may directly measure PM2.5 levels at their workplace and convert them to the equivalent AQI value (Cal/OSHA, 2019). You can view the current air quality index here.

If the AQI for PM2.5 exceeds 151 (designated as an “unhealthy” level) but is below 500 (designated as a “hazardous” level), employers are required to notify employees, provide training on health and safety relating to wildfire smoke, provide respiratory protection for voluntary use, and, if possible, implement engineering controls and/or change work procedures to reduce worker exposures (Cal/OSHA, 2019).

If the AQI for PM2.5 exceeds 500, employers are required to provide compliant respiratory protection to employees, and employee respirator use is required (Cal/OSHA, 2019).

What may employers need to consider moving forward?

· Implementing the hierarchy of controls is a prudent approach for minimizing worker exposure to wildfire smoke (NIOSH, 2015). Cal/OSHA requires such action to reduce employee exposure to PM2.5 to less than a current AQI of 151 (or as low as feasible if not achievable). Examples of controls include: 1) providing enclosed structures or vehicles with filtered air (engineering); 2) changing work locations and schedules (administrative), and 3) providing proper personal protective equipment (PPE).

· In California, employers are required to provide appropriate respiratory protection (e.g., NIOSH-approved N-95, N-99, N-100, R-95, P-95, P-99, or P-100) when the AQI reaches a threshold of 500, and for voluntary use when the AQI is in the range of greater than or equal to 150 and less than 500 (California DIR, 2019). Ensuring availability, training, proper use, and maintenance of PPE is critical. Employers should provide proper training and respirator fit testing in order to ensure that their workers are adequately protected when using respirators.

· Different populations will have different susceptibilities to wildfire smoke. For example, people with asthma and other respiratory diseases, pregnant women, and older adults may all be more susceptible to air pollution from wildfire smoke (USEPA et al., 2016). Employers should also consider the risks of respiratory protection for older adults and persons with respiratory diseases.

· If taking direct readings at a worksite, instrument accuracy is an important consideration. Under the new Cal/OSHA standard, any direct reading instruments used to measure PM2.5 at a worksite must be adequately calibrated, maintained, and used so that PM2.5 levels are not underestimated (Cal/OSHA, 2019).

· Every wildfire will result in a unique exposure profile, depending on the types and condition of materials burned, weather conditions, and the age of the smoke once it is inhaled (USEPA et al., 2016). The issue of wildfire smoke composition is further complicated by the spread of wildfires into populated areas since fires at the wildland/urban interface (WUI) also burn many additional types of materials present in housing and other structures (NFPA, 2019).

· The AQIs may not reflect all potential worker exposures from wildfire smoke. The EPA calculates AQIs for only five major air pollutants: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide (AirNow, 2019). Additionally, AQI monitors may not be located close to a given worksite. As such, the AQIs may not accurately reflect workers’ complete exposures to wildfire smoke at a given work site.

· While the long-term health effects of exposure to PM and other individual constituents in wildfire smoke are well-characterized, short-term, episodic exposures to the variable chemical mixtures represented in wildfire smoke are not (CDC, 2016USEPA, 2019). Different measures may be needed to protect workers from wildfire smoke exposure depending on individual wildfire duration and frequency, wildfire season length, and wildfire smoke composition.

· Certain areas will already have background air pollution present. When assessing the health risks posed by wildfire smoke, background air pollution present in a given area from normal industrial, commercial, and personal activities will also need to be considered.

Cardno ChemRisk scientists have evaluated exposure profiles and dose-response relationships for complex mixtures resulting from wildfires, air pollution, and industrial emissions. Cardno ChemRisk has a number of industrial hygienists and environmental health professionals who can assess exposure and risk of adverse health effects in specific settings. If you have any questions or would like more information about our environment, health, and safety capabilities, please contact Rachel Zisook.