Image: The Sand Fire near Santa Clarita, California, U.S. in July 2016. Credited to Getty Images and Attila Adam.

This post is a continuation of the discussion between AIHA’s chief science officer, Michele Twilley, DrPH, CIH, and Dawn Bolstad-Johnson, MPH, CIH, CSP, FAIHA, about the assessment of structures that have been damaged by fire. Their conversation covered instrumentation, sampling and analysis, issues for homeowners, forthcoming guidance from AIHA’s Real-Time Detection Systems Committee, and other aspects of post-fire assessments. Bolstad-Johnson is CEO and founder of Kaizen Safety Solutions in Phoenix, Arizona.

The first post in this series was published on March 11, 2025. The following transcript has been edited for length and clarity.

Michele Twilley: When you're talking about evaluating a house, you're not necessarily talking about one that was burned. You're talking about one that was in the smoke nearby or adjacent to a burn zone. Is that correct?

Dawn Bolstad-Johnson: That's partially correct. Fire damage occurs in three forms.

The first is thermal damage, which could be where the paint gets bubbly because it was in the heat envelope. It could also mean that part of the structure was burned.

Next is non-thermal damage, which is particle intrusion—the fire smoke, soot, char, and ash, chloride anions, and maybe heavy metals that have been deposited into the home or around the home.

And the last is chemical contamination, where the fire emissions can absorb or adsorb into and onto porous building materials and contents.

A conflagration of a neighborhood may also include single homes or a small cluster of homes that are left standing for no logical reason. The standing homes should be evaluated for all three types of fire damage: thermal, non-thermal, and chemical contamination.

I've inspected homes where the roof, for example, looks fine visually, but I referred the homeowner to a roofing specialist to inspect the roof for fire damage, and they found that all layers of the roof were melted together from the heat envelope, so it didn't appear to be obvious thermal damage. The fire actually stopped at the home next door, but seven homes in a row were burned down to incineration on the other side of that. The home next door to them was destroyed beyond repair, but it wasn't leveled down to ash, like all the other homes.

With the lithium batteries that are in consumer products such as hover boards, cars, and computers, and the overall synthetic and plastic load in homes, typical house fires are burning much hotter than they ever used to. So even though the house was maybe one door down, the heat envelope could have exceeded 1,000 F. Some of those fires are burning at 2,000 F or more. That is why the homes are literally incinerated. In the pile of ash, you don't see a dishwasher or a washing machine. They're simply gone. Sometimes all that is left is a brick chimney. But the appliances are gone. The couches are gone. Sometimes you'll see a remnant of a car. The beds are gone, but you might see the springs. It looks like an apocalypse.

Whatever was in all those homes that burned collectively creates a plume of smoke with everything in it: chloride anions, sulfide anions, lead, heavy metals, aldehydes, VOCs, acid gases, carcinogens, hydrogen cyanide, etc. Smoke is the transport vehicle that carries this toxic mixture into everything in its path including standing homes. If a home survives a conflagration, it's like a blessing and a curse at the same time.

If a home or structure survived the fire, the smoke is going to go through your home. Think of it as a staged filter. The smoke and all of the chemistry that comes with it will penetrate the exterior walls, get around the windows, and get into the window frames, the attic spaces, the wall cavities. There may be larger patterns of deposition near doors and windows, because homes aren't hermetically sealed. And what industrial hygienists don't realize, or maybe they've forgotten along the way, is that the wall cavities are actually breathing. Somehow, we understand that there can be mold in wall cavities, but we forget that the same principles apply to fire smoke. Fire smoke and all its constituents can go in a lot more nooks and crannies. Therefore, if the wall cavities are not being inspected, the level of smoke intrusion is not known. This also includes ductwork for supply and return registers and the HVAC unit itself. Note that the unit does not have to be on for smoke to find its way through the ductwork.

The built environment now is like a box that's just holding on to the smoke, the fire debris, the chemicals, and all this stuff is swirling around. And now the porous stuff in the house becomes the reservoir. For example, porous furniture has likely absorbed or adsorbed all the fire gases and everything that was in that smoke. So has the drywall. I've mined cyanide from a fire out of drywall up to seven years later.

The fire emissions act very similarly to chemicals in a meth lab. If a meth lab were to be discovered in a hotel room, remediation would include tear-down to the studs because the methamphetamine has absorbed into the drywall, the carpet, the drapes. And meth can be mined out of the walls years later. I'm finding the same thing with cyanide contamination.

Most post-fire inspectors are not recognizing that smoke is the transport vehicle for all these toxic gases and particulates. Look no further than the fire service. There's a cancer epidemic in firefighters because of the level of carcinogens they are exposed to from fire smoke. I think we should recognize that it's not different smoke for the firefighters than for the homeowners. It’s the same smoke. I think the difference is the firefighters are only at the fire for an hour, and they're at more of an acute exposure. The homeowner is often forced to move back into a standing home, and they have chronic exposure to all the fire emissions chemistry that has now absorbed or adsorbed into their building materials and contents.

I often get calls from homeowners after homes have been cleaned—meaning that all visible fire debris has been removed—looking for solutions to health problems. They call me and say their dog has health symptoms, and then like two weeks later their whole family has the same symptoms and they’re getting sick and they don't know what to do. And they’ve done everything that they were asked and directed to do. And they don't understand why they’re still getting sick. I try to explain to them that the reservoir is still there, the reservoir of all those chemicals that have absorbed into the drywall and into the insulation potentially, into the wood. They have just absorbed in because the house was hit so hard by the smoke and hurricane-level winds.

At the end of the day, the only things that can be salvaged without testing are glass and metal things. Everything else that is porous and capable of absorbing or adsorbing chemicals and particles is potentially damaged.

This idea that you can vacuum a couch and make it like new or wear your clothing again after it's been exposed—you know, if I'm finding cyanide in your wall, I wouldn't recommend wearing the clothing that was left behind in your house. Your skin is your biggest organ, and now you're exposed to every gas that was in your clothes, and we know we can't get all the fire residues out.

I believe that some people don't want to know because they love their house and their neighborhood and they just want to get back to normal, so they don't want the testing. Other people, after all the remediation has been done, they go back in their house, and they get bloody noses. I've sampled homes after they've been treated with ozone, which EPA doesn't even recommend. The house looks like a model house. It looks amazing. And the cyanide levels in the air are still high.

What's being solved for is what you can see with the naked eye, and you can see the soot, char, and ash. Maybe you can see some residues on a wall or on a shelf, but that's all that's being addressed.

I published the characterization of firefighter exposures during overhaul in 2000. That study was conducted when many people didn't have flatscreen TVs and computers in their homes. That wasn't the norm like it is now, and you didn’t have the number of people working from home then like you do now. There are more printers at home, more electronics, and there are old electronics in the garage because we don't know what to do with them. When that all burns, we treat it like it's a forest fire and just get a mop and clean it up, and that's not enough.

And I think that's where the huge disconnect is. We're not appreciating the level and complexity of fire emissions in these conflagrations of neighborhoods. We all have hazardous materials in our homes, whether it's oven cleaner or brake cleaner or brake fluid or our little cache of oil and spray paint. We've all got a little collection of that stuff in our garage, and it's all up in the smoke. Rubber from bicycle tires and car tires. It's just very, very complex.

If you’re only sampling the soot, char, and ash that you find in the patterns by the doors or the windows, that's not really determining the extent of damage. It's only verifying that you saw soot, char, and ash, and it could bias the remediator or the restoration expert that all they need to clean is by the doors. I've sampled homes where it was very heavy by the door, and then I sampled the center of a room where it didn't look like there was anything there to the naked eye, and it had char and ash. Sometimes the impacts are colorless or clear. It doesn't always have to be black. And in that case, we also found cyanide in the drywall. Those are a couple indicators that the problem may be much bigger than a vacuum cleaner can solve.

Michele Twilley: Can you talk a little about the work that the Real-Time Detection Systems Committee is doing with wildfires?

Dawn Bolstad-Johnson: We've been working on developing a sampling plan for post-wildfire. It's a guide for exactly what we've been talking about: identifying what stuff is in the fire so you can set up your sampling plan appropriately. The entire guidance document is based on science, not opinion. All guidance points back to peer-reviewed, published work.

We feel this guide is needed for cases in California right now. The industrial hygiene community is overwhelmed, and we don't have enough industrial hygienists to sample all these homes. The homeowners don't know about industrial hygienists or what a certified industrial hygienist brings to the table, which is different from an indoor air quality specialist. What they know is they have an indoor air quality problem or an indoor air quality concern. So they'll call the indoor air quality people in the phone book. They're mainly people who have taken 40-hour classes, and they're out there sampling for mold, asbestos, and lead, and they get the fire call. They're not turning it away. They're taking that call, and they're calling the lab that they use for mold, for example, and saying, “Hey, I just got a fire call. What should I do?” And the lab will direct them to maybe sample for soot, char, and ash using a tape lift. The lab in some cases will give an opinion on the results, and the untrained investigator accepts the lab interpretation on whether the materials analyzed are from a fire.

The industrial hygienist is supposed to interpret the lab results not just based on the results themselves but the details of where the sample was collected, what the conditions are, what the observations were, and so on. If the lab is making a determination on whether you have fire impact, I don't think that's appropriate. But the air quality specialists are out of their league.

We thought that by providing this guidance document, at least there would be something out there on how to approach post-fire sampling, whether it's a house fire, or a car fire in the garage and all that smoke got into the house, or a conflagration of a neighborhood, or a wildfire that spread into urban areas. Everyone would have guidance on how to approach sampling post-fire environments because there's no one-size-fits-all. The conditions are different in every case, so you really have to do your homework before you develop your sampling plan and understand your instrumentation if you are choosing to use direct-read equipment. For example, a PID cannot detect some of the most common fire emissions. So if the PID is reading zero, maybe the inspector should question whether they have the right tool to do this evaluation.

Resources:

American Industrial Hygiene Association Journal: “Characterization of Firefighter Exposures during Fire Overhaul” (September-October 2000).

National Academies of Sciences, Engineering, and Medicine: “The Chemistry of Fires at the Wildland-Urban Interface” (2022).

National Academies of Sciences, Engineering, and Medicine: “Why Indoor Air Chemistry Matters” (2022).