Wildfires are increasing, especially in the last decade. The trend may continue into the foreseeable future, and worker safety is an issue. Wildfire smoke can severely impact the health of communities, not only personal and economical but public health issues.

Wildfire contributes to air pollution by first, emission of pollutants, and second, the production of secondary pollutants like ozone. Particulate Matter (PM) is a concern from wildfire smoke because of the short-term exposure to workers fighting the fire and communities surrounding the wildfire.

Wildfire Workers in Utah
Wildfire Workers in Utah
Image by Scott Stringham

Fine particles from wildfire smoke and coarse particles from ash can irritate the lungs and cause coughing, wheezing, and difficulty breathing.

Most healthy people will recover quickly from wildfire smoke exposure and will not suffer long-term health consequences. Certain high-risk groups, including the elderly and those with compromised immune systems or heart, lung, or other diseases, are compromised when breathing the particles.

The testing of dust particles is essential for determining the accuracy of occupational dust in a wide range of industries but is of interest in the Wildfire setting. To improve protective measures for wildfire workers, a significant push in aerosol monitoring of workers is moving to real-time monitoring of PM. Real-time monitoring measures and reports live aerosol concentration, alerting the user of dangerous exposure levels.

Currently, on the market, there are two dominant technologies when it comes to personal real-time aerosol monitoring: Optical Particle Counters (OPC) and photometers. Both technologies utilize laser as a detection source; however, each has pros and cons.

How do they compare?

Both OPC’s and photometers are optical instruments that do not directly measure mass but can be calibrated to the sampled aerosol’s material properties to infer it. OPC’s are designed to measure and size individual particles where photometers measure multiple particles at the same time.

Since OPC’s are sizing individual particles, the technology is independent of particle size distribution when measuring mass concentration. However, to accurately measure mass concentration, the photometer must be calibrated to a particular particle size distribution. If the sampled aerosol’s particle size distribution changes, the photometer will fall out of calibration, such as in the wildfire situation.

AQI in Canada, Australia, and the USA

The Air Quality Index (AQI) is a unit of measure that runs from 0 to 500. The higher the AQI value, the greater the amount of air pollution is, and therefore the more significant the effect of air pollution is on humans. Different countries have various levels of AQI.

In the United States, the following table depicts the health risks. (Reference AirNow)

AQI Basics for Ozone and Particle Pollution
Daily AQI ColorLevels of ConcernValues of IndexDescription of Air Quality
GreenGood0 to 50Air quality is satisfactory, and air pollution poses little or no risk.
YellowModerate51 to 100Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.
OrangeUnhealthy for Sensitive Groups101 to 150Members of sensitive groups may experience health effects. The general public is less likely to be affected.
RedUnhealthy151 to 200Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
PurpleVery Unhealthy201 to 300Health alert: The risk of health effects is increased for everyone.
MaroonHazardous301 and higherHealth warning of emergency conditions: everyone is more likely to be affected.

In Australia, the following table depicts the health risks (Australian Unions)

Australian Union AQI
An AQI less than 50 indicates that the air quality is good. At this low level, a person can spend time outdoors and air pollution will pose very little risk to their health. As the AQI number increases, so does the risk to human health.

In Canada, the following table depicts the health risks. (Reference Wikipedia)


Risk: Low (1-3) Moderate (4-6) High (7-10) Very high (above 10)

To see the health effects in relation to PM 2.5 (µg/m3)

Wildfire PM2.5=AQI Correlation
Wildfire PM2.5=AQI Correlation

PM levels specified by AQI are for wildfire particulate. Most real-time instruments use Arizona Dust to calibrate the instruments. NIOSH blog and chart indicates that if we don’t calibrate the real-time instrument with the type of particles that we will measure, the percentage error could be as large as 55%.  In Nanozen lab, we calibrate the DustCount wildfire monitors with wildfire particulates to increase the accuracy of the Optical Particle Counter (OPC) similar way as NIOSH suggested.

Use of Real-time Respirable Dust Monitors

Real-time respirable dust monitors can help in determining the health risks of wildfires by instantly providing a reading of the particle counts. Typically the Respirable Dust Monitors, like the Nanozen DustCount, are used in both outdoor and indoor situations such as a mine or laboratory to find small particles such as silica.

According to the blog, The Use of Real-time Respirable Dust Monitors by National Institute for Occupational Safety and Health (NIOSH), several respirable dust monitors were tested using a controlled dust chamber. The manufacturer calibrated each monitor. ISO A1 Fine Arizona Road Dust was used, and the manufacturer calibrated each monitor. The following is the chart that demonstrates the correction factor for ISO A1 Fine Arizona Road Dust.

Correction Factor for ISO A1 Fine Arizona Road Dust
Correction Factor for ISO A1 Fine Arizona Road Dust

Laboratory Testing

In a controlled laboratory setting, a series of tests ran by Nanozen demonstrated and were analyzed to find the differences between OPC’s and photometers.

The photometer performed well over a broader concentration range than the OPC and is more suitable in scenarios with exceedingly high dust concentrations, given that the aerosol size distribution is well-characterized.

However, the OPC, unlike the photometer, performed accurately with multiple particle size distributions. Occupational scenarios that create variation in particle size distributions, such as changing worker location, changing processes, and the presence of numerous point sources of different aerosols, would be where the OPC would excel.

The tests concluded that a photometer would need recalibration for each sampling convention where areas an OPC would not.

Field trials were then conducted particularly in a wildfire site where OPC determined the particle distribution of wildfire particulate where more than 90% of particulates are below 2 micrometers. The following chart depicts the results.

Sizes and concentrations of Wildfire particulates detected in 2018 Fire in British Columbia, Canada to help guild the setting of Permissible Exposure Level (PEL) in industrial settings.

Sizes and concentrations of Wildfire particulates detected in 2018 Fire in British Columbia, Canada
Sizes and concentrations of Wildfire particulates detected in 2018 Fire in British Columbia, Canada

This blog was written by Linda Rawson, who is the founder of DynaGrace Enterprises (dynagrace.com), an authorized distributor of the Nanozen DustCount.  The Nanozen DustCount is available on the GSA Schedule.  For further information, please connect with Linda on LinkedIn, or contact her at (800) 676-0058 ext 101.