The health impacts of wildfires: Frequently asked questions
We compiled a list of all of the questions we’ve received from people in the LA area in the wake of the Eaton and Palisades fires earlier this month, and spoke to environmental health researchers Kari Nadeau, Joe Allen, Mary Rice, Amruta Nori-Sarma, and Vanessa Kerry to get answers to these pressing questions.
- Questions about Air Quality
- Questions about Children and Schools
- Questions about Household Cleanup
- General Questions
Air Quality
Q: Why is wildfire smoke harmful to people?
Wildfires produce a complex mixture of air pollutants, including fine particulate matter, referred to herein as PM2.5; this denotes small solid particles and liquid droplets in the air that are smaller than 2.5 micrometers in diameter, which is roughly 20-30 times smaller than the diameter of a human hair. Since these particles are so small, they are easily inhaled deep into the respiratory system, which can cause a myriad of negative health effects. These can range from coughing and throat and nose irritation to exacerbated asthma symptoms, altered heart and lung function, heart attacks, and even premature mortality, particularly among those with underlying health conditions. One study estimated chronic health impacts from indoor exposures to various air pollutants and found PM2.5 to account for the greatest burden, making them especially important to protect ourselves from.
While there are ambient particles every day in the air we breathe, the high toxicity of wildfire smoke is due to a combination of the higher concentrations of particles in the air during and after wildfires, as well as differences in the chemical makeup of the particles that form during wildfires. Different material burnt leads to different types of particles, which can also cause different health harms.
More research is still needed about what might be in the air after an urban wildfire, and how long it will stay in the air, but we know that for weeks, if not longer, exposure to particles in the air is a risk for everyone.
Q: Who should wear a mask and when?
Experts are advising everyone in proximity to the burn areas to wear a mask out of an abundance of caution. We recommend wearing a mask while outside, for at least a month after the fire. It is most important to mask if you see or smell smoke in the air, and the mask should be at least an N95 (or KN95). Surgical or cloth masks used during COVID will not protect from the fine particles contained in wildfire smoke.
For those who are more at risk of adverse effects (include people with underlying respiratory and cardiovascular conditions, children, infants, pregnant people, and people over 65), we recommend masking for up to 100 miles away from the fire.
One way to think about exposure is exposure over time within closer proximity to the burn area: so, the longer you will be outside, and the closer you are to the burn area, the more important it is to wear a mask. To limit exposure, it is best to limit time outdoors, especially doing strenuous physical activity.
This recent article from the NY Times features recommendations from Dr. Kari Nadeau and Dr. Joe Allen, and has important tips for choosing a mask, indoor air purifiers, and even fitting masks for young children.
Q: For how long after the fires are contained/put out, should we continue to mask outdoors when the AQI is yellow or above?
Experts recommend masking for at least a month after the fires are contained or put out.
Q: Which air purifiers are best for filtering out pollutants from wildfire smoke inside your home?
You want to use an air purifier with a HEPA filter, which will be effective for cleaning particles in smoke from inside your home. Your air purifier doesn’t need to have a UV or ionization option. If you’re looking for specific brands, check out this NY Times Wirecutter Review for some recommendations.
You can look for the ‘clean air delivery rate’, or CADR, that the manufacturer should report. This is an indicator of the effectiveness of the device, so you can make sure it’s sized correctly. Our rule-of-thumb is to look for a CADR of about 300 for a 500 square foot room.
For those who are closest to the burn area with a home directly impacted by soot and ash, there are also air purifiers that have HEPA filters combined with an activated carbon or activated charcoal filters. These air purifiers can help capture the particles (the HEPA filter) and also gases (the activated carbon filter).
Also, if you have central air conditioning or heating in your home, upgrade your HVAC filter to a Minimum Efficiency Reporting Value (MERV) 13-rated filter or higher. MERV ratings signify an air filter’s effectiveness at lowering airborne particles and pollutants, determined by the smallest particle it’s capable of trapping (in microns). It is also recommended to always change your filter immediately following a fire, as wildfire smoke can affect filter performance.
To ensure the air inside your home is healthy, Healthy Buildings recommends following the “hierarchy” of good indoor air quality, which focuses first on source control, then ventilation, followed by air cleaning. Here we present strategies specific to wildfire smoke:
- First, you want to limit the amount of polluted outdoor air that makes its way indoors. Start by closing all windows and doors, and ideally seal up any noticeable cracks or openings in exterior walls (i.e., reduced infiltration).
- If possible, do not use swamp coolers or whole house fans that bring in outside air. In this case of wildfires, you actually want reduced ventilation.
- Next, use an indoor air filter to clean the particles from your indoor air, this can be a portable HEPA air filter or a MERV13 or higher filter on your central air system (or a combination of both).
Learn more here: https://healthybuildings.hsph.harvard.edu/protecting-your-health-from-wildfire-smoke-spotlight-on-filters/
Q: How far away from the fires do we need to be concerned about health impacts and air quality?
Q: If I live in between two burn zones, does this mean I am safe or more at risk?
Q: If I was out of town when the fires happened, is it safe to return home if it is only a mile from the burn site?
Q: How far from the burn zone is considered a safe proximity?
Q: How far might the polluted air travel?
Many of these questions are difficult to answer because there is still a lot of uncertainty. Even people 50-100 miles away from the affected area could experience adverse health effects from the fires. The Harvard T.H. Chan School of Public Health, along with UCLA Fielding School of Public Health and other local partners, has just announced a 10 year study to investigate the health effects of the fires. I encourage you to reach out to Dr. Joe Allen and his study team to request your property be tested and monitored by emailing forhealth@hsph.harvard.edu.
In general, we’d recommend using these 3 questions as a guide to determine the level of precaution you might want to take:
- Did you see it? If you saw – or still see – visible dust or ash, you should take the extra precautions we provided in this document.
- Can you smell it? If you are still smelling smoke and/or ash and/or ‘fire smell’, that is most likely the off-gassing of chemicals that have absorbed into materials in your home or school. If you can smell it, you should take extra precautions.
- Can you sense it? If you are unsure, we recommend purchasing one of the portable air quality sensors listed in our guide. Look for one that measures airborne particles (PM2.5) and airborne gases (TVOCs). These are imperfect measures, but will give you a sense of how your space is being impacted or not. For more information on these sensors, and how to interpret the data, you can read this article. The article is written for businesses, but the information on sensors and what they measure are relevant for homes and offices, too: Harvard Business Review: It’s Time for Companies to Monitor Workplace Air Quality
Regardless of your distance from the burn zone, watch out for symptoms of smoke exposure such as dizziness, coughing, chest pain. These symptoms can occur even 5 days after exposure to an AQI of 80+. If you experience these symptoms, please see a doctor immediately.
Q: How can we monitor dangerous airborne substances which aren’t included in the AQI shown by most weather websites?
Q: Can you recommend an air quality tester?
The Air Quality Index (AQI) as published by airnow.gov is an excellent way to see what is generally happening with air quality outside your home, but it might not be accurate down to your exact location, and it can’t capture the quality inside your home. The AQI measures ground-level ozone, particulate matter (fine PM2.5 and coarse PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
To check the safety of the indoor air in your home, you will want to look for an air quality monitor that measures fine particles (PM2.5, in addition to volatile organic compounds (VOCs) and carbon dioxide (CO2). Read a recent NY Times Wirecutter review of air monitors here.
Q: Ash is everywhere, is this toxic?
The ash could be potentially toxic. Complex chemical reactions from burning things like paint, furniture, building materials, cars, electronics, and more can potentially make ash toxic. A lot of items in homes are made of petroleum and different composites that can be extremely hazardous when they combust. People who are involved in recovering ash could face increased health risks from inhaling potential toxins. Scientists are still trying to understand the health impacts of those chemical changes on human health.
Residents should not attempt to remove or clean hazardous fire debris themselves. Post-fire house debris is hazardous because it can contain toxic materials like asbestos, lead, mercury, chemicals from household products, and other heavy metals which are released into the ash and debris when structures burn. These materials pose a risk to health if inhaled or handled improperly. Planning is underway for Debris Removal Activities in coordination with the County Office of Emergency Management and our State and Federal Partners. Residents should check recovery.lacounty.gov frequently for updates on the debris removal program.
Once the local government has determined that it is safe to re-enter your property, or if your home was not located in a burn zone, you may still want to consider hiring a professional clean-up crew. There are fire remediation companies that can be hired to help assess your home for fire or smoke damage, support clean up and advise on safety.
If you enter a property with visible ash to examine the damage or recovery items, it is important to mask, wear gloves, and be as cautious as possible. We recommend wearing a high-grade respirator (ie, mask), specifically a P100+multi-gas mask. These can be purchased online and at local hardware stores.
Children and Schools
Q: How does wildfire smoke impact young children — particularly during pregnancy — and what can communities do to protect children both during and after a wildfire?
Although wildfire smoke affects everyone – it is especially harmful to young children and pregnant persons. During pregnancy, exposure to wildfire smoke can trigger the body’s inflammatory response, which can lead to problems such as gestational hypertension, preeclampsia, low birth weight, and preterm birth. Preterm birth is associated with poor health outcomes later in life, including impaired cognition, reduced growth, and chronic health issues.
Young children are also at risk of adverse health effects during and after wildfire episodes. Children have higher rates of respiration and more active systems than adults, making them more likely to inhale high levels of harmful particles during outdoor playtime. Young children have increased rates of emergency visits for asthma after exposure and higher rates of upper respiratory infections, pneumonia, and bronchitis. Wildfire smoke exposure is also related to poor learning outcomes. A nationwide study found that students with exposure to smoke a year leading up to a test, particularly on school days, had lower average scores, the more smoke they were exposed to.
To protect children during and after a wildfire, children should wear N95 masks, or if they are too young to mask, they should have as little exposure to outdoor air as possible. Children should also be exposed to clean air spaces. Schools, daycares, business, and other places where children spend time should have clean air shelters with well-sealed windows, and central air systems should be fitted with filters that are rated MERV13 or higher. Filters in portable units must be changed after a wildfire since reactions with the smoke can cause them to be more ineffective.
Learn more about the impact of wildfire smoke on children in this new brief from the Center for the Developing Child at Harvard University:
Q: How important do you think it is for schools to have a carbon filter (in addition to HEPA) in the air purifiers in each classroom?
The most important thing is to ensure that there is good filtration in the classroom by upgrading and changing out filters in the air handlers (e.g., MERV13 filters) and using portable air cleaners with a HEPA filter. Each classroom does not necessarily need to have a portable air cleaner with a carbon filter in addition to HEPA.
HEPA filters are excellent at capturing airborne particles, and carbon filters can be effective at capturing gases. However, there are limitations to carbon filters (e.g., most don’t have a lot of carbon and the filter can ‘saturate’ very quickly (meaning, they no longer capture gases); it’s hard to predict when they will saturate because it depends on many unknowable factors; they are expensive.)
We would recommend the decision of whether to use carbon filters be based on how impacted the school was. For example, if your school is close to the burn area and had visible soot/ash, it’s likely that porous materials absorbed smoke and can off-gas for many weeks. These schools need a deep-cleaning, and should consider discarding porous materials and, if not discarded, these materials should be given time to off-gas (this requires good ventilation). After cleaning, and as an added precaution, highly impacted schools could opt for these portable air cleaners with carbon – just look for one with HEPA filters and as much carbon as you can find. There are models that have 15-30 pounds of activated carbon.
Q: Is it safe to send kids to school, particularly as clean-up and rebuilding begin?
Schools that are impacted should be thoroughly cleaned before re-entry. Ideally air, water, dust, and soil testing should be completed, in particular for schools nearest to the burn area. In addition, we recommend enhanced filtration after the cleaning, and installing air quality monitors in classrooms to measure airborne dust (e.g., PM2.5) and airborne chemicals (e.g. TVOCs).
Q: Do we need to get rid of school supplies that were exposed to ash and smoke?
This will depend greatly on where your home/school was located and how close it was to the burn zone and smoke/ash from the fires. If you want to act out of an abundance of caution, items that should be discarded include items made from porous materials, or items that easily absorb smoke. These include paper items such as schoolbooks, fabric-based materials such as backpacks and clothes, and plastic-based items.
Here are some resources to look at when deciding what items to get rid of or how to proceed with cleaning:
- https://calrecycle.ca.gov/disaster/wildfires/homeowners/,
- https://www.maca.gov.nt.ca/sites/maca/files/resources/returning_home_safely_after_a_wildfire_-_may_2023.pdf
Household Cleanup
Q: What do you recommend to reduce toxins that are brought inside from pets?
After going on walks outdoors, wipe your pets’ paws and coat with a damp cloth. Also consider bathing pets more frequently if they are going outside a lot. Also, continue to damp wipe areas of the home where outdoor dust can be brought in easily (e.g. entryways), and vacuum regularly. Use a vacuum with a HEPA filter that is air-sealed. Some vacuums will pick up soot and dirt and capture the big particles but then redistribute smaller particles back into the air. This article explains why you want a HEPA filter, and why finding a vacuum that is air-sealed is important: Are HEPA Vacuums Worth It? Think Twice Before Spending Big. | Reviews by Wirecutter
LA County put together this helpful fact sheet about caring for pets after the fires: http://publichealth.lacounty.gov/vet/docs/WildfirePetSafetyFactSheet.pdf
Q: What household items need to be replaced?
This will depend greatly on where your home was located and how close it was to the burn zone and smoke/ash from the fires. Sifting through debris is not recommended as it can be very dangerous. LA County has a helpful resource about what their cleanup teams are removing from damaged properties here: https://recovery.lacounty.gov/returning-after-fire-faq/
If your home was not in a burn zone but you are worried that your home was exposed to smoke/debris from nearby burns, you should discard most food items, including jarred items that may have been exposed to heat or smoke. Cleaning products, paint, batteries, and electronics should be thrown out to mitigate risk as well.
Please check the LA County Recovery website for details about property cleanups and timelines for your neighborhood: https://recovery.lacounty.gov/returning-after-fire-faq/
There are also fire remediation companies that can be hired to help assess your home and belongings for fire or smoke damage, support clean up, and advise on safety.
Q: How do you clean surfaces in your house?
Residents should not attempt to remove or clean hazardous fire debris themselves. Post-fire house debris is hazardous because it can contain toxic materials like asbestos, lead, mercury, chemicals from household products, and other heavy metals which are released into the ash and debris when structures burn. These materials pose a risk to health if inhaled or handled improperly. Planning is underway for Debris Removal Activities in coordination with the County Office of Emergency Management and our State and Federal Partners. Residents should check recovery.lacounty.gov frequently for updates on the debris removal program.
If your home was not in a burn zone, but you are worried about smoke/ash inside your home, please keep the following tips in mind. Different types of surfaces need to be cleaned differently. When cleaning, always wear household dishwashing gloves, long sleeve shirts, and long pants, to avoid the ash irritating your skin. We recommend wearing a high-grade respirator (ie, mask), specifically a P100+multi-gas mask. These can be purchased online and at local hardware stores.
Also wear safety goggles, not glasses, so that ash won’t get in your eyes. To clean up ash, try gentle sweeping and then wet mopping, trying not to stir the ash into the air. HEPA filter vacuums can be used, but do not try to use a standard household vacuum. Ash can be discarded in the regular trash, but make sure to put it in a plastic trash bag first so the ash doesn’t blow away. For more recommendations, please visit the LA County Recovery guidelines for clean-up after a fire: https://recovery.lacounty.gov/returning-after-a-fire-public-health/
General
Q: What other reliable sources of current health info can we turn to in the coming months?
Aside from the resources that we have included in this newsletter, be sure to stay up to date on current health information by looking for articles with new research. There is a lot of new health information that is shared online as more research about the effects of the fires is conducted. Also, be sure to check local and state government websites, that have a lot of helpful information about how to best protect yourself.
