Note: This information has been compiled as a resource for our community. The authors of this content are scientists, engineers, and professors who have not been specifically contracted to perform this service and are not experts on fire remediation. Readers should assess their own risk and common sense to determine actions that they want to take. Read the main article on how to mitigate post-fire smoke impacts in your home for more information. 

What am I smelling?

Smoke is a combination of fine particles, volatile organic compounds (VOCs), and many other reactive gases. What you smell are the VOCs, some in gaseous form and others attached to microscopic particles. When the hot smoke penetrated homes, these VOCs condensed on interior surfaces such as walls, furniture, curtains, etc. The VOCs are now slowly off-gassing, and the odors will diminish over time.

When is it safe to go back to my home?

The human nose is a very sensitive instrument and many chemicals that can harm your health have odors, but others do not. It’s best to use professionals or clean your home as suggested in the main article before you reoccupy it. Ventilation and additional filtration (as suggested below) can lower your exposure to harmful chemicals as the VOCs off-gas from walls and other surfaces in your home over time.

If you start to notice non-specific health effects (such as headaches, eye irritation, and nosebleeds) it may be from contaminants that are irritating but not odorous or below your detection limit. New York State has a good overview of odors and human health. The ATSDR (Agency for Toxic Substances and Disease Registry) has a database to look up common odors by their smell characteristics or by their chemical ingredients.

What about the use of ozone and hydroxyl generators to eliminate smells? 

Despite their common usage by professionals for odor remediation, we don’t recommend these devices due to the lack of studies on their effectiveness for fire smoke-damaged homes, and possible unintended negative consequences. If you do decide to use them, stay out of the home while the ozone (or hydroxyl) generator is operating, and then air out the home (preferably with open windows and doors) for three hours before re-entering (based on calculations for tobacco smoke remediation). We also recommend temporarily removing indoor plants, artwork, and other materials susceptible to ozone damage. 

Ozonation (using an ozone generator) is a common remediation approach to eliminate odors from tobacco smoke, fire damage, and mold in unoccupied homes, hotel rooms, and cars. High levels of ozone (which is toxic to breathe and has a sweet, pungent smell like chlorine or an electrical spark) chemically react with VOCs condensed on walls and other surfaces and change their chemical nature – generally to more volatile compounds that off-gas quicker, but also unknown byproducts that may linger. While little information exists to assess its overall effectiveness, a study of tobacco smoke in a room-sized chamber found that nicotine and PAHs adsorbed onto polyester fabrics were effectively eliminated. Formation of more volatile (as intended) but toxic byproducts (such as formaldehyde, other carbonyls, acetone, and ultrafine particles) was observed, further emphasizing the importance of staying out of your home during the ozonation process and airing it out afterward. Another concern is that high ozone levels can damage indoor plants and materials in the home (such as paints, rubber, other natural materials, electrical wire coatings, and fabrics and artwork containing susceptible dyes and pigments).

Other odor remediation devices are marketed as safe for occupied spaces with labels such as hydroxyl, hydroxyl radical, reactive oxygen, and active oxygen. In some cases, these are falsely labeled and should be checked against the California Air Resources Board’s listing of Potentially Hazardous Ozone Generators Sold as Air Purifiers. Hydroxyl radicals are very reactive and would likely be consumed very quickly by chemical reactions with gases commonly found indoors (such as VOCs and nitrogen dioxide), and are therefore highly unlikely to affect odorous VOCs condensed on walls and other surfaces. Some of these reaction byproducts are toxic.

It is also important to recognize that these devices are different from air cleaners, which are intended to be used when a space is occupied. In this case, we recommend the use of HEPA (High Efficiency Particulate Air) filters for particles and activated carbon filters for VOCs, and to avoid ionic and other types of electronic air cleaners. These latter devices produce unintended chemical reaction byproducts that can be even more harmful. See the main article for recommended brands, and below for further advice on selecting and operating an air cleaner and technologies and brands to avoid. 

How can I monitor the air quality in my home?

The low-cost sensors discussed here are not as sensitive or accurate as the more expensive instruments that government agencies and scientists use to monitor air quality. But they do produce useful data that can let you know if you have elevated levels, and measure changes (for example, if they are reduced after cleaning or when you have a new filter or better ventilation in your home). Indoor pollutants of concern include microscopic particulate matter (a major health concern) that can penetrate deep into the lungs, Volatile Organic Compounds (VOCs, including toxics and odor-causing compounds), nitrogen dioxide (of health concern from gas stoves and other combustion sources), and carbon dioxide. Sensors for particulate matter and Total VOCs tend to be semi-quantitative measures since these pollutants are complex mixtures of many compounds and the sensors vary in their sensitivity to specific compounds.

The South Coast Air Quality Management District in Los Angeles conducted a comprehensive evaluation of low-cost sensors that can measure particulate matter and gases (primarily nitrogen dioxide and ozone) against regulatory monitors outdoors. PurpleAir particulate matter sensors performed well in these evaluations and have the advantages of relatively low cost ($200 to $250), detection of distinct particle sizes ranging from ultrafine particles (more likely to contain odor-causing VOCs) to dust, and many other users in our County that share data on outdoor and indoor levels. 

The Indoor Environment Group of Lawrence Berkeley National Laboratory evaluated 16 low-cost sensors with a variety of indoor sources under varying conditions of temperature and relative humidity. Total VOC sensors Awair, Foobot, and uHoo showed a strong correlation with professional-grade monitors despite a poor quantitative agreement, so they can be used to see if your mitigation measures improve the situation. Awair Second Edition rated best overall on particulate matter and carbon dioxide levels, temperature, and relative humidity, but unfortunately, neither it nor Awair Element ($299) are readily available.

More accurate but higher-cost (several thousands of dollars or more) professional grade options for Total VOCs used by scientists include the Aeroqual Photoionization Detector (with 10.6eV lamp), the Ametek-Mocon Baseline VOC‑TRAQ II, the GrayWolf AdvancedSense Pro (with IQ-610 Indoor Air Quality Probe with 10.6eV lamp), the GrayWolf VOC-103L Probe (with ppb PID sensor and 10.6eV lamp), and the RAE Systems ppbRAE 3000 (with interchangeable 10.6eV and 11.7eV lamps).

The EPA Sensor Toolbox includes information about how to use a sensor. 

An FAQ list put together by some of the world's experts on airborne transmission of COVID-19 includes information on how to monitor ventilation using a low-cost carbon dioxide sensor.

Your own nose can be a more sensitive instrument and any unusual, strong odors are an indication that further mitigation is needed as discussed in the main article.

Will a vacuum be sufficient to clean up ash?

The EPA recommends a vacuum cleaner equipped with a HEPA (High-Efficiency Particulate Air) filter system when cleaning surfaces contaminated with ash and other dust. The use of a typical household or shop vacuum should be avoided since they do not filter out small particles, but rather blow them out of the exhaust into the air where they can be breathed. Consumer Reports has identified HEPA vacuums with the lowest emissions. If you have no other option, vacuum (or wet mop) in well-ventilated conditions (windows and doors open) and protect yourself and others as described next.

How do I protect myself when cleaning up ash in my home? 

The ash in your home from the fires can be harmful to your health. The EPA recommends these steps to protect your health:

• Wear a well-fitted NIOSH (National Institute for Occupational Safety and Health)-certified mask or respirator:
  • Such as an N95 mask or more protective respirator (look for “NIOSH” and “N95” or “P100”)
  • Surgical and cloth masks will not protect you. 
  • Facial hair can get in the way of a well-fitting mask.
• Wear gloves, safety goggles, long-sleeved shirts, long pants, and shoes with socks to avoid contact with ash or debris. If you get ash on your skin, in your eyes, or in your mouth, wash it off as soon as you can.
• People with heart or lung disease (including asthma), older adults, and pregnant women should avoid cleanup activities as much as possible.
• Keep children and pets away from ash and cleanup activities.

Boulder County has more information on how to safely clean up after a fire (also en español).

Can I add more filtration to our forced-air heating system?

Most systems have filters (the “blue wool” ones) that are not very effective for the smallest particles that bind to toxic VOCs and penetrate deepest into our lungs. Upgrade to MERV 11- or 12-rated filters (for example, 3M Filtrete 1000 and 1500 filters available for $10-$15 in hardware stores, Target, online, etc.) and add 1” foam around the edges or tape over any gaps in the filter holder. These filters have a white cloth-like material and are pleated for a larger surface area to capture particles and prevent a significant pressure drop. Change your filter monthly until the smell goes away.

Should I be concerned about my attic?

If your air ducts are intact, it is unlikely that chemicals in the attic will move throughout the house. A detailed study of a single-family house in northern California found that a tracer compound released from the attic did not show up elsewhere in the house, either in summer or winter.

Should I add a stand-alone air cleaner?

If the odors are strong and concentrated in one area – or you want to avoid having your forced-air system on all the time – consider purchasing portable air cleaners with both a HEPA (High-Efficiency Particulate Air) filter and an activated carbon filter. The carbon filter is important as it will remove the VOCs that cause the smell from the air. The HEPA filter will remove 99.97% of particles, including VOCs that are bound to particles. These units are also effective at reducing general particle pollution, coronaviruses, woodsmoke, airborne pollen and pet dander, cigarette smoke, etc. See the main article and below for further advice on how to select and operate an air cleaner.

What about ionic and other types of electronic air cleaners?

Ionic air cleaners are generally ineffective at removing particles and VOCs. This applies to other types of electronic air cleaners such as ionizers, electrostatic precipitators, photocatalytic oxidation (PCO) devices, hydroxyl generators, and devices with UV light components. Some technologies can generate ozone at levels that are unsafe to breathe, especially if they are not certified by the California Air Resources Board – see certified air cleaners here (for safety only, not pollutant removal effectiveness). They have also listed Potentially Hazardous Ozone Generators Sold as Air Purifiers.

What is CADR and how do I use it to select an appropriate stand-alone air cleaner for a room?

The AHAM (Association of Home Appliance Manufacturers) developed the AC-1 test for a CADR (clean air delivery rate, in cubic feet per minute) of tobacco smoke, fine dust, and pollen. The CADR is the volume of clean filtered air delivered each minute by an air cleaner, and our recommended brands (in the main article) have CADRs ranging from 100 to 500 cubic feet per minute. Tests are conducted by an independent laboratory and reported here. Use the results for the tobacco smoke CADR because these smaller particles penetrate deepest into the lung and are also the most likely to contain the VOCs that cause odors. The room size recommendations (roughly 1.5 times the CADR in square feet for a normal ceiling height of 8 feet) are based on our recommended five air exchanges per hour in the room. Most homes in the winter have less than one air exchange per hour with clean outside air so an air cleaner can be an important supplement. It will be expensive to equip every room with an air cleaner, but even one for each level (located in a central point) or just moved to the main room that’s occupied at the moment will be helpful.

Is there a CADR test for VOC removal?

Unfortunately, not at the present time. AHAM is developing the AC-4 test to measure a CADR for VOCs, but it will take at least a year for the methodology to be approved and manufacturer results to be available. If you’re particularly concerned about VOCs, Wirecutter recommends the Austin Air HealthMate HM400 because of the large amount of activated carbon (15 pounds), but it's more expensive ($715), noisier, and uses more electricity than other air cleaners intended for larger rooms. We’ve had good personal experience with cooking and wildfire odor removal with other brands, and we suggest looking at buyer reviews for odor control feedback.