Working Safely When the Air Quality Index Is High

By Daniel Clark
Last updated: July 6, 2024
Key Takeaways

While employers can’t control the quality of outdoor air, there are important controls you can implement to protect outdoor workers from the harmful effects of air pollution.

2023 has been, and continues to be, the most severe wildfire season in recorded North American history, with the severity eclipsing even the newsworthy California fires of 2020. Beginning in June, wildfires in Alberta spread out of control, prompting evacuations as the flames crawled toward populated areas – something we also saw in the 2016 Fort McMurray wildfires in Northern Alberta.


A state of emergency was declared, the military got involved, and it became a big news item. I happen to live in Alberta and this was obviously a subject of local interest. It was also being covered in Canadian provinces where fires were also raging. But the hubbub became went international when the smoke got picked up on the wind carried outside the country.

In early June, tourist pictures snapped from the New York harbor looked like vintage photos taken 100 years ago. The yellow-brown air gave the images a sepia tone, as if they had been passed through a filter. That unusual color was due to smoke from wildfires in Quebec and Nova Scotia blanketing the northeast US, at one point giving New York City the worst air pollution of any major city in the world.


This level of air pollution has very noticeable effects, even indoors. Much like it was up here in Canada, breathing in the smoke made people feel progressively unwell with symptoms like headaches, chest pain, fatigue, and nausea. This was a serious problem, especially for people who worked outdoors and simply couldn’t avoid it. As they did at the start of the COVID-19 pandemic, safety and health professionals were suddenly scrambling to figure out how to keep workers safe.

Quantifying the Risk: The Air Quality Index

There is, unfortunately, only a shallow pool of research on how outdoor smoke affects workers as an isolated category. But we can piece together risk information from public health information and exposure guidelines to known smoke components.

That is, however, only looking at part of the picture. Many compounds are more hazardous in combination than they are in isolation, so we just don’t know for sure how bad exposure is.

The US Environmental Protection Agency (EPA) has developed the Air Quality Index (AQI) as a way to quantify this hazard. The Index uses a sampling of “PM2.5” (particles of solids and liquids in the air with an aerodynamic diameter of 2.5 micrometers or less) to rate outdoor air quality on a scale of 0 to 500, with a higher number indicating worse air quality.

This scale represents six different levels of risk:

  • 0 – 50: Good
  • 51 – 100: Moderate
  • 101 – 150: Unhealthy for Sensitive Groups
  • 151 – 200: Unhealthy
  • 201 – 300: Very Unhealthy
  • 301 – 500: Hazardous

A “Moderate” AQI is generally considered safe and will only adversely affect people who are particularly sensitive to atmospheric contaminants. An AQI that falls in the “Unhealthy” category will affect the general population, not only those with sensitives. The “Hazardous” range indicates harmful conditions that require everyone to take precautions.

During the California wildfires, the state government mandated companies to limit the AQI to 151 or less indoors in order to remain below the threshold specified as “Unhealthy for Sensitive Groups.” Indoor AQI in the 151-500 range required an employer to provide suitable respirators (such as N95s) for voluntary use that conform to the usual use and care guidelines, including a fit test. It’s likely that orders like this will later be incorporated into larger, national and international standards.

Air Quality Index chart describing who is affected by AQI levels and what measures they should take to stay safe.Source: EPA

Smoke may be grabbing the headlines, but it isn’t the only factor in air quality. The AQI (and other related indices) take into consideration concentrations of other common compounds that have adverse health effects, such as:

  • Nitric oxide
  • Carbon monoxide
  • Methane
  • Nitrogen dioxide
  • Ozone
  • Other oxides and hydrocarbons

All of these arise from an array of natural and industrial processes, and have to be considered as part of a comprehensive understanding of what we’re breathing in. Smoke, for example, is a combination of dust, droplets, gases, fumes, and vapors, so simply measuring the weight of particulate in a unit sample of air misses quite a bit.

(Find out How to Complete a Respirator Fit Test)

Protecting Workers from Hazardous Outdoor Air

When the outdoor air quality took a nosedive, employers wondered whether this came with any corresponding safety obligations. In some jurisdictions, employers have specifically codified responsibilities; in others, they are simply under the general duty clauses. If there are recognized hazards that can affect the health or safety of workers, the employer has a general obligation to put controls in places. Failure to do so can be construed as negligence in the event that an incident occurs or a health condition develops.

But what can they do about a global event?

Indoors, employers have some measure of control over the working atmosphere. It’s possible to modify the operation of an HVAC system to reduce fresh air intake during periods of anticipated high ground level smoke. Doing so will temporarily recirculate the same air throughout the work environment. While that isn’t typically ideal, it is useful for times when the recirculated air is of better quality than the air outside the facility. There is a limitation, however, at least according to conventional standards that currently don’t make dispensations for outdoor air quality. ASHRAE provides standards for HVAC systems which specify air turnover volumes and required percentages of fresh air for specific systems. While they outline minimums for fresh air intake, they don’t currently weigh the downside of drawing in polluted air.

Other measures include using active air purifiers with HEPA filters, installing electrostatic precipitators, or improving the seal integrity of the building envelope.

That’s well and good for indoor workers, but what can an employer do to keep their outdoor workers safe?

For all the efforts spent on managing indoor air quality, there’s little to be done for the air outside. That’s bad news, considering some parts of the east coast reported AQI levels of 400!

Outdoor air pollution is a hazard that employers cannot eliminate. Engineering controls like ventilation systems are also inadequate for outdoor spaces. The bulk of the controls will be administrative ones, such as job rotation, scheduling, increased rest periods, and moving tasks inside whenever possible. As a last line of defense, workers should be provided with adequate PPE, such as particle respirators.

The most important thing for employers will be keeping an eye on the forecast – as they already do for outdoor work. Many of the same considerations that go into dealing with extreme heat (another thing we’re seeing a lot this year) also apply to smoky weather, so scheduling around the forecast is going to become more and more vital. The movement of smoke and other air pollutants are directly influenced by the weather, particularly wind speed and direction, so it is not beyond our ability to model, monitor, and predict it in the short term.

(Learn about The Basic Types of Respirators – And How to Select the Right One for Your Workplace)

Air Quality Affects Everyone

Watching a satellite view of the fires’ smoky tendrils doing a lap around the earth provided a sobering reminder that we all share the same atmosphere. Air quality is going to impact everyone, far and wide, indoors and out. Unfortunately, there is no reason to think this increase in wildfires is a transient event. It’s far more likely that we’re facing an emerging norm. Employers that drag their feet, thinking they can treat air quality as an acute event rather than a chronic one, are misguided. This kind of thinking will cause them to fall behind – and to start seeing health effects and claims that impact their companies and industries.

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Written by Daniel Clark | Safety and Quality Management System Specialist

Daniel Clark

Daniel Clark is the founder and President of Clark Health and Safety Ltd., providing safety and quality consultation across various industries in Calgary, Alberta. Daniel has a Bachelor of Science degree, certification in health and safety, certificates in both CAD design and CNC, auditing certifications and the designation of Canadian Registered Safety Professional. Being raised and practicing in Calgary, the heart of Canada’s energy industry, most of Daniel’s career has been energy related. He has performed safety and quality roles from field supervision to office-based administration and management. Daniel’s consulting business has worked with organizations offering engineering services, restoration, pipeline, environmental, manufacturing and food service.

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