What types of pollutants do urban wildfires release?

Emissions from wildfires in urban areas can include particles or particulate matter (PM), volatile organic compounds (VOCs), metals, and other hazards like lead and asbestos.

What is the AQI?

AQI stands for air quality index. The AQI measures ground-level ozone, particulate matter (fine PM_2.5 and larger PM₁₀), carbon monoxide, sulfur dioxide, and nitrogen dioxide. The U.S. AQI is the EPA’s index for reporting air quality. The official AQI is reported on the AirNow.gov website by EPA monitors. Other websites such as PurpleAir, report data from their network of privately-owned air quality monitors in homes.

AQI does not, however, measure VOCs, metals, or other harmful pollutants that may be present after wildfires.

What are VOCs?

VOC stands for volatile organic compounds. VOCs are gases that are emitted into the air from solids. This can happen after structures burn during wildfires, but VOCs are also commonly emitted in homes from an array of everyday sources like cleaning products, air fresheners, paint, new furniture, etc. Some of these VOCs are harmful to human health.

What is off-gassing?

Off-gassing is the production of gases from the chemical deterioration of a substance over time, and the release of gases from materials into the air. Source: EPA Indoor Air Glossary 

For example, when you light a scented candle, the heat from the fire melts and releases chemicals from the wax to help freshen the smell in your home. This a similar process to the off-gassing that happens over time as chemicals are released from solids inside your home.  

After a fire, this off-gassing can include more hazardous compounds due to the chemicals that are likely present in ash and debris from the fire. As the ash and debris get stirred up and moved (by cleaning activities, turning on the HVAC system, etc.), they can begin to emit fine particles and VOCs into the air.  

This is why it is important to air out your home frequently in the days after a fire. This allows the VOCs to dissipate from your indoor environment.  

This is also why it is advised to wear a protective mask and take other precautions when entering a home that was affected by the fire, or is located in a burn zone, even if the home itself was not damaged. 

What is PM_2.5 and why does it matter?

Air pollution is often measured by measuring the number of tiny particles in the air. These particles, called particulate matter (PM) are made up of a mixture of many different chemicals. PM varies widely in size, shape and chemical composition, and may contain manmade chemicals, metals, organic compounds, carbon, and many other compounds.

Particles are defined by their size for air quality regulatory purposes. Those with a diameter of 10 microns or less (PM₁₀) are inhalable into the lungs and can induce adverse health effects. For comparison, a human hair is 50-70 microns in diameter.

Fine particulate matter is defined as particles that are 2.5 microns or less in diameter (PM_2.5). PM is more likely to travel into and deposit on the surface of the deeper parts of the lung. PM_1.0 is a subset of PM_2.5 and contains even smaller particles.

The EPA and CA Air Resources Board have both set limits for exposure to particulate matter in air. These limits are based on scientific studies that show that exposures to these pollutants for certain amounts of time are associated with an increased risk of adverse health effects. These limits look at two types of exposures:

• High exposures over a short period of time (less than 24 hours)
• Lower exposures on a regular basis over a long

Source: CA Air Resources Board (CARB)

Which air purifiers are best for filtering out pollutants from wildfire smoke inside your home?

You want to look for 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.

What is a HEPA filter and why do I need one?

HEPA stands for high efficiency particulate air [filter] (as officially defined by the U.S. Dept. of Energy). According to the EPA, “This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns corresponds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e. 99.97% or better for all particle sizes).” Learn more about HEPA filters on the EPA website here.

HEPA filters can be found on portable air purifiers and air cleaners, as well as on household and industrial vacuums.

What is a MERV rating?

MERV stands for Minimum Efficiency Reporting Values. These ratings report a filter’s ability to capture larger particles between 0.3 and 10 microns (µm).  The MERV rating is derived from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). This value is helpful in comparing the performance of different filters The higher the MERV rating the better the filter is at trapping specific types of particles. A MERV-rating of 13 or higher is recommended for HVAC filters in order to reduce airborne particles in your home. Learn more about MERV ratings on the EPA website here.

Can you recommend an air quality monitor? 

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 measure the quality inside your home.

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 WIRED review of air quality monitors here.

What is the difference between an N95 face and a surgical mask?

The FDA regulates surgical masks and surgical N95 respirators differently based on their intended use. The below information is from the FDA website here.

A surgical mask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. These are often referred to as face masks, although not all face masks are regulated as surgical masks. Note that the edges of the mask are not designed to form a seal around the nose and mouth. Surgical masks will not protect from the fine particles contained in wildfire smoke.  

An N95 respirator or mask is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles. Note that the edges of the respirator are designed to form a seal around the nose and mouth.

The FDA advises the following precautions when wearing an N95 mask:

• People with chronic respiratory, cardiac, or other medical conditions that make breathing difficult should check with their health care provider before using an N95 respirator because the N95 respirator can make it more difficult for the wearer to breathe.
• Some models have exhalation valves that can make breathing out easier and help reduce heat build-up. Note that N95 respirators with exhalation valves should not be used when sterile conditions are needed.
• All FDA-cleared N95 respirators are labeled as “single-use,” disposable devices. If your respirator is damaged or soiled, or if breathing becomes difficult, you should remove the respirator, discard it properly, and replace it with a new one. To safely discard your N95 respirator, place it in a plastic bag and put it in the trash. Wash your hands after handling the used respirator.
• N95 respirators are not designed for children or people with facial hair. Because a proper fit cannot be achieved on children and people with facial hair, the N95 respirator may not provide full protection.

Should I wear an N95 mask? When and Why?

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.  

During the COVID-19 pandemic, there were many concerns about fake N95 masks being sold online. The CDC developed this resource to help you determine if your N95 mask is genuine and NIOSH-approved. (NIOSH is the National Institute for Occupational Safety and Health: the federal agency responsible for testing and approving respirators used in U.S. workplace settings.)

What is a respirator and when do I need one?  

A recent advisory from the Healthy Buildings Program at the Harvard T.H. Chan School of Public Health highlights when to wear a respirator or N95 mask, and which type of cartridges to use.  We recommend using a P100+multigas respirator if you are in the burn scar area and/or cleaning soot/ash. If you’re outside the burn scar area and don’t have visible soot/ash, and if the Air Quality Index (AQI) is ‘very unhealthy’ or ‘hazardous’, then we recommend a N95 respirator. 

Read the full recommendation here: https://hsph.me/wildfiremasks 

How do I know if there are dangerous contaminants inside my home?

The Harvard Healthy Buildings team recommends 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. If you can smell it, you should take extra precautions.  
• Can you sense it? If you are unsure, we recommend purchasing a portable air quality sensor to monitor your indoor air quality. Look for one that measures airborne particles (PM2.5) and airborne gases (VOCs). These are imperfect measures, but will give you a sense of how your space is being impacted or not.  

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. 

How do I get VOCs and other potentially toxic substances out of the air inside my house? 

If you still see soot and ash in your home or smell chemicals, you should ventilate to help these materials “off gas”: 

• Open windows 
• Run A/C (make sure you have a MERV-13+ filter on your HVAC system) 
• Run air purifiers if possible – we recommend HEPA for filtration of particles and of VOCs.  

However, make sure not to ventilate or air out your home when there are outdoor conditions that may bring more harmful materials inside. 

For example:  

• ❌️DON’T ventilate when there are debris removal activities on neighboring properties.  
• ❌️DON’T ventilate on windy days when ash and debris are more likely to be kicked up into the air.  
• ✅️DO ventilate the day after it rains (when the air is typically cleaner) and when there is no cleanup or debris removal happening nearby.  

If you see clean-up or debris removal happening nearby, that is when you should try to prevent outside contaminants in the air from coming inside. This map shows the location of planned debris removal activities for both the Palisades and Eaton fires, which can help you know when to avoid ventilating your home. 

To reduce contaminants from entering your home: 

• Close windows 
• Turn off HVAC systems 
• Run air purifiers and air filters in your homes 
• Avoid working outside while this cleanup work is happening 

Healthy Buildings recommends these 3 things to improve air quality inside your home: https://healthybuildings.hsph.harvard.edu/3ways-reduce-risk-wildfire-smoke-home/ 

How can I protect myself when working inside an affected home (i.e., a home in a burn zone)? 

Due to the likely contaminants in soot, ash, and fire debris, even in homes that did not burn, we recommend wearing protective masks and clothing when entering a home in the burn zone. 

If possible, hire a professional remediation company to remove the soot, ash, and fire debris before entering the home yourself. If that is not possible, take the following precautions to avoid exposure to potential toxins in affected homes. In general, try to wear the most protective gear that you can afford and can find.

Recommendations:

• When entering an affected home, always wear a well-fitting high-grade respirator (mask).
• When cleaning, always wear a protective outer layer that you can easily remove when leaving the burn site, and try to minimize exposed skin to avoid skin irritation.
  • You can do this by wearing household dishwashing gloves, long sleeve shirts, and long pants.
  • For more protection, you can wear a disposable Tyvek “bunny suit.” These can be purchased online and at local hardware stores.
• Wear safety goggles, not glasses, so that ash won’t get in your eyes.
• Cover your head to avoid ash from sticking in your hair.
• Wear thick-soled shoes or boots, and be sure to clean the soles of the shoes thoroughly when leaving the burn site.
• After you leave the affected home, remove the outer layers of protective clothing and clean the soles of your shoes (preferably while outside so that you don’t track ash and toxins into where you are staying), and wash or discard dirty items. Be sure to shower and wash skin and hair with soap and water.

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/ 

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.  

If your house has already been remediated, or if you live outside the burn area but are still concerned about smoke and air quality in your home, you can take these steps to remove smoke from your personal items: 

• You can wash all clothes, linens, and any other fabrics (curtains, etc.) that may have absorbed smoke in hot water with a strong detergent. 
• Wash fabric items that can be washed (area rugs, curtains, etc.) in separate loads in your washing machine. 
• If possible, have wall-to-wall carpets and upholstered furniture professionally cleaned. You can also rent steam carpet cleaners at your local grocery and hardware stores if professional cleaning is not possible. Please see below for precautions to take while cleaning. 
• If you are still concerned about any items, you can dispose of them according to the instructions provided by your local waste removal service. 

How should I clean surfaces in my home?  

If possible, residents should not attempt to remove or clean hazardous fire debris themselves. Post-fire house debris can be hazardous because it may 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. Debris Removal Activities are underway in coordination with the County Office of Emergency Management and 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: 

• Wear a protective layer of clothing and a mask to prevent exposure to debris and contaminants. Read our full list of PPE recommendations here.
• Vacuums with HEPA filters should be used to clean up ash/soot, but do not try to use a standard household vacuum. 
• Use wet mops and rags to clean hard surfaces (tile floors, countertops, cabinets, etc.). Do not sweep dry ash with a broom as this can stir up toxins into the air. Spraying ash and dust with water first helps to contain and minimize the amount of particles that become airborne. 
• Ash, dirty rags, etc., can be discarded in the regular trash, but make sure to put them in heavy duty plastic trash bags (i.e. “contractor bags”) first so the ash doesn’t blow away. 

For more recommendations, please visit the LA County Recovery guidelines for clean-up after a fire.

Should I drain my pool?

If you have visible contamination in your pool and are interested in participating in a study to assess its water quality, you can volunteer to enroll here.   

LA County Department of Health recommends the following procedures to clean your swimming pool after a fire:

• Clean the skimmer baskets of debris and skim water surface of the pool with a pool net to remove floating debris.
• Brush the sides and the bottom of pool to loosen contaminants, then vacuum pool.
• Backwash and clean the filter(s). Release waste and wastewater into a municipal sanitary sewer only. If connected to a septic tank system, release the backwash to a pervious surface like gravel, lawn, or open space to allow for infiltration without erosion.
  • Backwashing into the storm drain system (alleys, driveways, streets, storm drains) and creeks is prohibited by law.
• Check pH and adjust level between 7.2 and 8.0.
• Check free chlorine level and adjust level to a minimum of 2.0 ppm for a pool and 3.0 ppm for a spa.
• Ensure the recirculation system is operating properly by checking filter pressure and/or the flow meter.
• Reopen pool only when pH levels are between 7.2 to 8.0 and the free chlorine is at a minimum of 2.0 ppm for a pool and 3.0 ppm for a spa.

For more information, please contact the Environmental Health Division, of the LA County Department of Health’s Recreational Waters Program at (626) 430-5360 or rhealth@ph.lacounty.gov.

Is my tap water safe to drink? 

A recent article from the Sierra Club highlights a concerning finding of benzene levels in the tap water of homes in the burn zone of the Eaton fire. Some areas in the City of Pasadena, Los Angeles, and water utilities including Lincoln Avenue Water Company issued a Do Not Drink order in the days after the fire due to the potential risk of consuming benzene and other contaminants. 

Gregory Pierce, research and co-executive director at the UCLA Luskin Center for Innovation, told the Sierra Club:  “If you’re not in area that burned, and you don’t have a notice from your drinking water system, you should not have any new concern about your drinking water quality because of the fires,” he says.  

However, if you are in an area that was affected by the burn, you should take extra precautions. The CA State Resources Control Water Board recommends the following: 

• When returning to a residence or business, first check your local water quality notice before assuming the water is safe to drink. 
• Follow any water quality notices issued by your local water provider. Instructions for using safe water will be listed on the water quality notice. 
• If your area is under a water quality notice, bottled water and clean water filling stations may be available in your area. Check with your water company for potential bottled water points of distribution. 
• If you have damaged or destroyed property, water quality on the customer side of the meter may be impacted. Contact your local water provider to discuss assessing your property for water quality impacts. 
• If you can operate water on your property, performing low-flow flushing is a common tool that customers can use to bring fresh water into their water lines. Continually refreshing water in the lines could help lessen or limit water quality impacts you may experience.