January 23, 2025 / An Interview with Enrique Medina by Michele Twilley

The LA Fires: Considerations for the Public

Image: The Thomas Fire burning in Ventura and Santa Barbara counties, California, United States, between December 2017 and January 2018. Credited to Getty Images and Carsten Schertzer.

As first responders make progress containing the fires burning in the Greater Los Angeles area, authorities are allowing some evacuated residents to return to their homes. AIHA’s chief science officer, Michele Twilley, DrPH, CIH, recently spoke with Enrique Medina, MS, CIH, CSP, FAIHA, about the hazards potentially faced by returning residents and people living downwind of the fire in the coming days and weeks. Medina is the editor of AIHA’s Technical Guide for Wildfire Impact Assessments for the OEHS Professional and the president and CEO of Alliance Consulting International in San Diego, California.

This post is the first of two that present transcripts of Twilley’s conversation with Medina. It has been edited for length and clarity. Last week's post, an interview by Twilley with Michelle Rosales, MPH, CIH, covered preparing for evacuation and concerns for returning residents. A subsequent post with Twilley and Medina will focus on challenges facing OEHS professionals responsible for workplaces and communities affected by the fires.

Michele Twilley (MT): What kind of message would you like to convey to members of the public about wildfires?

Enrique Medina (EM): For returning residents, the California Department of Public Health and LA County have some guidance on what to do when you come back (PDF). Additional information for people affected by the fires is available from the state and from the California Environmental Protection Agency Office of Environmental Health Hazard Assessment (PDF). If your house burned and you're looking through the debris for things to save, you really have to worry about exposures to particulates and toxic metals that can be in the residual ash and char.

For people who were fortunate enough to have their house survive, the first thing you want to do, if you go in, is to clean the accumulated fire residue that settled on surfaces in the house. Whether you're looking at volatile organic compounds (VOCs) or polycyclic aromatic hydrocarbons (PAHs) or some acids, what's airborne is a smaller part of what’s present. And any kind of ventilation that you utilize initially, as soon as you close the windows, the VOCs are going to off-gas and get in the air again. So, until you clean the settled particles, you're going to have reservoirs, which are places where particulate matter is absorbed or transformed into something else.

Attics in particular are places where smoke infiltrates and leaves fire residue. Many houses have the indoor air intake to the air conditioning units in the attic or plenum, so, if you turn it on, you could be putting that fire residue back into the house. Insulation probably will need to be replaced. Those issues will happen later as part of the smoke damage restoration, but if you are coming into your home for the first time and you smell that fireplace odor or burnt smell, you want to be really careful. You don't want to be in that environment until you either do basic cleaning by the occupant or by a professional restoration company.

MT: Are there any recommendations you would make for using PPE to protect yourself while you're picking through a debris pile, looking for a treasure?

EM: I would start at the bottom. Use good, sturdy shoes with good soles. There are going to be a lot of puncture hazards. Wear long pants and a long-sleeved shirt, and a good N95 mask at a minimum. And if you're entering the remains of a structure, or picking through debris, you need safety goggles and nitrile gloves under some thicker leather gloves.

You shouldn't enter a structure that looks compromised. Look at the outside to see if it's got thermal damage or even structural damage.

When you leave, you need to decontaminate. If you're a resident, you don't want to track contaminants into wherever you're staying, so have the shoes you're going to wear for looking around and then have another pair of shoes to wear in your car and back at your temporary housing. Also, change your clothing or wear something over it that you can take off. If you're going to be moving stuff around, a disposable Tyvek chemical-resistant “bunny” suit may be a good idea. Do not wash clothes you wore in a burned house together with your other laundry. If you're entering a house that survived the fire, at a minimum, you should wear gloves and an N95 mask. A cartridge respirator with a HEPA (high-efficiency particulate air) filter and organic vapor cartridge filters is more protective, but it needs to be fit tested and you need a medical clearance to make sure the respirator does not impair your breathing.

MT: How about people living downwind from the smoke of the burning fires? What should those residents do?

AQI meter
You can search for your local Air Quality Index reading by entering your zip code or location on EPA’s website. The results indicate which pollutant the AQI is based on—in this case, PM2.5 (see gray box).

EM: Look at your car to see if it's covered by ash. If it's not, then you have a much lower risk level. Before approaching the area, see if there is an Air Quality Index reading. You can find the AQI by entering your zip code or location on EPA’s AirNow website. That will tell you whether you should even be doing extra-strenuous work. For people who are otherwise healthy, if the AQI is more than 100, certainly at 150, you're really taking a risk. From some of the pictures I've seen while the fires are going on, I'm sure the AQI was above 300. So that should inform you whether you even want to be outside. The AQI measures fine particulates such as PM2.5 and other pollutants. The AQI level shown is for the pollutant with the highest reading. If you’re going to be outdoors and you are also concerned about VOCs in the air, check the AQI for ozone level as well, because VOCs in the air produce ozone by reacting with sunlight. [Editor’s note: see image at right.]

If you're downwind from the fire and the AQI is a little high, look for visual evidence of ash on your car or in your backyard, and then go into your home and look at infiltration points like doorways and windows. Look for signs of infiltration in the form of char, ash, and soot.

Wear an N95 respirator while you are in the house. If you have a low-cost air quality sensor, use it. You can see what the air quality is inside your house, at least for particulates. If you're going to do some cleaning, be sure to use a vacuum cleaner with HEPA filters that trap particles down to 0.3 microns from the exhaust airstream, so the dust doesn’t go back into your house. Follow with wet-wipe methods. Don't do any dry sweeping.

You need a safe place for your pets, because they're closer to the ground. Follow the same precautions for the pet that you would follow for a human, except for wearing respirators. But it is important to see how they act. Look at anything you left behind that could have been exposed to wildfire residue, like pet food and water, and throw them away.

After the 2018 Camp Fire, the town of Chico had high levels of emergency room visits for respiratory, cardiovascular, and cerebrovascular effects and for asthma that continued for over two weeks after the fire. So even when the air quality improves, people who are susceptible may experience symptoms, and it's important for them to seek healthcare.

MT: Once the fire ends, it sounds like the risk continues for adverse health effects or impacts.

EM: It depends on the distance from the fire.

We're really looking at three dimensions when we look at air pollution from a wildfire. As the fire plume lofts upwards, it runs into the tropospheric air currents several miles up that move it downwind and eventually settle it back down. The second dimension is at ground level where people live and work. While the fire is burning, and even afterward, outdoor air quality is affected. And then you have the third dimension of the indoor air environment inside your home. It's good to get clues from one as it affects the others.

There are a lot of dilution effects, particularly in the high-altitude dimension. There's transformation that occurs in the environment. What they're measuring up in the stratosphere or the troposphere may not exactly be what you're measuring at ground level. What’s in the indoor environment depends on how much smoke infiltrated your home or your business, and what happens after you clean. The main health concern is at the ground level where people are breathing fine particulates.

Subsequent to the fire, there's the issue of re-entrainment. The ground is going to be contaminated with toxic chemicals and heavy metals, especially on a fire like this that burned so many homes and buildings. Anytime you track that dust indoors, you raise the possibility of having some wildfire particulates and toxic substances.

MT: We're hearing a lot about the Santa Ana winds and the effect that they're having on fanning the fire. People who aren't on the West Coast are not familiar with the Santa Anas and how the wind changes direction or calms. How would that affect somebody near a burn zone?

EM: Well, the Santa Ana winds, first of all, they're very dry. So, the humidity, which at least in coastal California is normally around 60 to 80 percent, drops to 20 percent, sometimes even lower.

The Santa Ana winds come from inland and go toward the ocean, so that pushes the air pollution out into the ocean. However, the prevailing winds in Southern California are onshore winds, which bring the pollution back inland. If you consider LA a source of air pollution during a Santa Ana episode, San Diego will get the pollution after a one- or two-day delay when the onshore winds return. So, for people who are downwind, from an air pollution or air quality standpoint, you have to keep monitoring afterward.

The other thing about the Santa Ana winds is they exacerbate the drying that already occurred from having a dry season. A lot of the plants that are adapted to our weather have a lot of resins, so they can combust very quickly. Smaller fires that continue over a week or two after the fire has been extinguished are very common. That's going to continue to affect air quality if you're downwind, even some distance away.

We look at time and distance from the wildfire source. The “near field” can be six to 10 miles from the fire. The local effects can go out to 60 miles, and the “far field” can exceed 100 miles, as we saw during the Camp Fire when air quality in San Francisco, over 120 miles away, was poor for more than two weeks. Until the wildfires are completely out and for a week or two afterwards, if you see visible signs of ash outside your house, or on your car or patio furniture, that is an indicator that there are still high levels of wildfire particulates in the air that can get into your home.

MT: What action should somebody take if they see ash on their car or signs of soot, char, and ash at infiltration points in their home?

EM: At infiltration points, the more you step into the interior of the building or house, the less accumulation you should see. It's really important to clean all surfaces. Start and finish with HEPA vacuuming—we call it the “HEPA sandwich.” In between you wet-wipe all the surfaces, including ceilings and walls. You want to start in the cleaner areas so that you're not re-contaminating your rags or whatever you're using to clean.

Do a thorough cleaning—you know, like family is coming to visit. Start at the ceiling and then work your way down. A lot of the sampling industrial hygienists do is on the tops of ceiling fans and other fixtures where people forget to clean. Wear your mask while you're doing that, and wear gloves. Then move out to the places that are more contaminated and clean those. Try to set up a system so that you're not tracking stuff when you're going back and forth, like having a mat outside or changing your shoes. Pets are going to be an issue, and so that is something you should keep in mind.

For your car, take it to the car wash. We don't want to contaminate the stormwater because that goes out to the bays and the ocean. In fact, I don't think we're allowed to wash our cars now with a hose because of water conservation measures.

MT: What if somebody sees infiltration in their home? Would air cleaners be effective?

EM: Air cleaners are effective. Use HEPA filters with activated charcoal to filter VOCs as well as particulates.

I did some work with schools, and having good air filtration really helps. For a central air conditioning system, install MERV 13 air filters. But a lot of systems cannot accommodate a MERV 13 filter. Even MERV 8 or 9 are good filters for industrial applications—the higher, the better.

Portable air cleaners or purifiers are good, but as soon as you turn them off, volatile and semi-volatile organic compounds can off-gas from surfaces. Check that the filters have what’s called the Clean Air Delivery Rate (CADR). It's an industry-sponsored rating, and the industry says a unit that has a CADR of 300 or above is a good air cleaner. If it's got a good filter, it should last at least a couple of months, unless the pollution is really bad. You do need to keep an eye on the filter. Try not to use filters that have ozonation features because they produce ozone that can irritate your lungs and eyes. We don't want that.

Some DIY air filters were promoted during the pandemic. You can make one out of a fan and a cardboard box. You put two filters on it, and those can be inexpensive.

Air filtration is good, but only if you get rid of the particulate residue.

To donate to LA wildfire relief efforts, visit thewebsite of the American Red Cross, select “Disaster Relief,” and then select“California Wildfires.”

Resources

AIHA: Technical Guide for Wildfire Impact Assessments for the OEHS Professional (2018).

AIHA: Wildfire Safey Resources.

AirNow: Air Quality Index (AQI) Basics.

California Environmental Protection Agency Office of Environmental Health Hazard Assessment: “Fact Sheet: Protecting Public Health from Home and Building Fire Ash” (PDF).

County of Los Angeles Public Health: “Returning Home After a Fire” (PDF).

State of California: 2025 Los Angeles Fires.

An Interview with Enrique Medina by Michele Twilley

Michele Twilley, DrPH, CIH, is AIHA’s chief science officer and staff certified industrial hygienist.

Enrique Medina, MS, CIH, CSP, FAIHA, is president and CEO of Alliance Consulting International in San Diego.

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