Abstract:

Wildland urban interface (WUI) fires produce extensive smoke caused by the burning of vegetation and buildings (e.g., framing, roofing, paint, cars, carpets, electronics, furniture, and other contents). Smoke from the fire contains toxic and hazardous substances, such as asbestos, lead, mercury, arsenic, and cadmium. (National Academies of Science: “The Chemistry of Fires at the WUI”) Smoke also contains a mixture of aerosolized particles and the vaporization of smoke, char, ash, dioxins, furans, and heavy metals. (California DIR “Respiratory Requirements During Fire Cleanup, Removal, and Demolition”; Newsweek “California Wildfires: How Smoke Harms Your Body;” Scientific American “What Makes Urban Wildfire Smoke So Toxic”) Ash and char are the main wildfire particles that may contain heavy metals, polycyclic aromatic hydrocarbons (PAHs), dioxins and furans. (AIHA: Technical Guide for Wildfire Impact Assessments for the OEHS Professional)

Some pollutants in fires are heavy metals, which are defined as metallic elements that have a relatively high density compared to water. With the assumption that heaviness and toxicity are inter-related, lead and beryllium for example can induce toxicity in humans at low levels of exposure. (Heavy Metal Toxicity and the Environment) However, in controlled amounts, not all metals are bad for us to inhale, eat, and drink, such as cobalt, copper, chromium, iron, magnesium, manganese, molybdenum, nickel, selenium, and zinc. These are essential nutrients that are required to maintain human biochemical and physiological functions. In other words, we need a certain amount of heavy metals around us all the time to maintain human and animal life, vegetation, and a balanced ecosystem. Therefore, after a vegetation wildfire or a WUI fire, removing all 100% of heavy metals in a house is not necessary or scientifically sustainable.

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The emissions from a WUI fire can vary depending on whether the fire burns homes, cars, or commercial areas; even a subset of these fuel types can vary, such as homes of different ages made of different materials. Emissions vary depending on fuel composition, fire characteristics, and the heating   dynamics that the fuels experience. Human exposure can vary greatly, depending on weather patterns during and after the fire, personal activities, and the living and working circumstances of the people exposed. While few data are available on emissions and exposures from fires at the WUI, knowledge of chemistry, emissions, exposures, and health impacts of wildland fires and urban fires can be combined to hypothesize characteristics of WUI fires. (The Chemistry of Fires)

As mentioned, wildfires generate a wide range of fire effluents (e.g., gases, vapors, and particles) that can enter structures, settle on horizontal surfaces, and absorb and adhere to ceilings, walls, flooring, cabinets, and contents. The extent of wildfire residue impact on buildings and infrastructure depends on the distance the house is from the fire area, the wind speed and direction, flaming, heat energy, and smoke. In addition, the conditions near and downwind of the fire (e.g., open windows and doors, attic ventilation, HVAC systems) are important factors to consider during environmental and restoration professional inspection.

Structures downwind that are indirectly impacted by the fires’ thermal pressure and smoke residue may not exhibit visible signs of heat damage, and they may not have visible evidence of wildfire residue contamination. Still, microfine particles, smoke vapors, gases, and residue can contain toxins and may be responsible for homeowners experiencing adverse health effects for weeks and months after the fire. Homeowner’s health concerns must not be ignored by environmental professionals and restorers.

Unless contamination is removed or otherwise neutralized, wildfire residue will continue to emit chemical vapors that cause odors to linger for extended periods. Therefore, the goal of restoration is to return the property to its pre-wildfire state. (AIHA: Technical Guide for Wildfire Impact Assessments for the OEHS Professional) To accomplish this, there are general cleanup guidelines for wildfire cleanup available to property owners and restorers from various sources (e.g., FEMA, Cal/EPA, Cal/OEHHA, Cal/DHA, the Colorado Department of Public Health and Environment), in Canada, the Canadian Environmental Protection Act (CEPA) and provincial agencies; in Australia, the National Emergency Management Agency (NEMA), along with state and territory agencies. Recognizing workers can be affected by smoke and its byproducts, employers are required to protect workers before allowing them to have exposure to hazardous substances. (OSHA) Before beginning work involving fire damage cleanup, a job hazard analysis (JHA) should be performed. (IICRC S700)

The complete removal or neutralization of every wildland fire particle, along with VOCs, SVOCs, PAHs, dioxins, furans, and heavy metals, is not scientifically feasible. What is feasible is using a systematic method of cleaning and restoration that may completely remove or significantly reduce lingering wildfire residue down to acceptable levels. In other words, the purpose of detailed cleaning is to remove wildfire particles and heavy metals from surfaces is to stop the spread of wildfire residue within the structure and exposure to human health. If after testing this cannot be achieved, a plan for removing porous materials and soft goods should be recommended.

In California, the current clearance criteria for lead dust in pre-1978 homes on hard surface flooring, is 10 micrograms per square foot (µg/ft2 or ug/m2). Meaning, lead levels above 10 µg/ft2 are not acceptable, where additional cleaning is required to either eliminate or lower lead levels. 

Apart from environmental professionals using the California EPA lead dust exposure value of 10 µg/ft2, California EPA has not established regulatory limits of surface concentrations of metals in residential dust that were brought into a home after a WUI fire. That said, the Center for Disease Control and Prevention (CDC) , there is no safe level of lead dust for children and babies to have exposure. Lead dust, in any amount is dangerous to infants, toddlers, and developing fetuses.

Even at low levels of exposure lead dust can cause neurological, behavioral, and mental damage. CDC and public health officials agree, all detectible levels of lead dust, even below federal standards, should be treated as hazardous in homes where children or pregnant women live. In addition, homeowners that did not have lead dust in their home and contents prior to a WUI fire, do not want lead dust in any amount.

The EPA methods and procedures for removing lead dust and other inorganic metalloid dust are not the same for removing smoke generated by organic vegetation and buildings and contents that burned. In other words, oils, tars, PAHs, VOCs, SVOCs, dioxins and furans, brought into downwind homes require different cleaning methods along with deodorization.
 

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Organic Combustion Byproduct Testing:

In most instances, tapelifts are preferred to be a non- destructive method for collecting and analyzing char, ash, soot, and other particles of interest, because these particles are the primary indicators of wildfire debris impact. Laboratory analysis identifies carbonaceous material (soot), fibrous material, char fragments, ash crystals, and biological particles.

Tapelift samples use clear adhesive tape to capture settled dust and transfer it onto a clean microscope slide where particles remain fixed in place, making it easy to analyze their structure and composition under a SEM (scanning electron microscope) and other microscope types. In other words, the tapelift sampling technique preserves the relative position, density, size, and shape of particles on the surface, as well as the population per unit area. Sampling methods and techniques follow ASTM D7910- 14(2021) and E1216-21.

Laboratory analysis using SEM-EDS (energy dispersive spectroscopy) can detect elemental composition that might detect metals, but tapelift sampling and analysis methods are not designed to identify heavy metals or their level. On the other side of the coin, alcohol wipes, detergent wipes, and Ghost wipes, are not designed to capture carbonaceous material (soot), char fragments, ash, and biological particles, because the wiping and chemicals in wipes destroy their appearance and structure.
 

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Inorganic Chemical Testing:

Recognizing the tight-rope environmental professionals walk on when meeting customer commitments, no matter who their customer is, they have the responsibility for pre and post testing, verifying cleaning work was completed correctly, therefore returning homes and contents back to pre-wildfire condition.

For structures within or near the fire impacted area, a detailed evaluation of the property should be completed by qualified professionals, and when necessary, tested to determine the extent of wildfire impact. The results of inspection and tests should lead to reasonable and necessary recommendations for cleaning and restoration. Once cleanup is completed, compare the initial data against a second set of data involving the post-cleanup verification testing.

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Environmental Professionals and Restorers Cleanup Strategies:

When lead dust is in wildland fire smoke that impacts downwind buildings, the primary responsibility of the restorer is worker protection before completing cleaning.

Unless there are structural safety issues that become primary for stabilizing the building, making it safe for workers to enter, the next process is the removal of lead dust which supersedes the removal of smoke residue and other contaminants.

The EPA methods for lead dust cleanup are not completely interchangeable with procedures for cleaning and neutralizing smoke residue.

Key factors in distinguishing differences between the cleanup of inorganic lead dust and organic smoke residue include: 

The Chemical Composition of Inorganic and Organic Contamination

Surface and Material Penetration Differences Affecting Cleaning and Testing

Cleaning Agents and Chemistry Requirements

Cleanup Criteria for Lead Dust and Smoke Residue

Re-Contamination Risks

Comparison Between Lead Dust, Wildfire Contaminants, and Human Health Effects

Conclusions:

The earth and its environment contain a balance in chemicals it produces. However, when wildfire occurs, the balance in biodiversity changes where vegetation becomes altered, damaged, or permanently destroyed. Burning mainly releases combustion byproducts, but it can release natural heavy metals in plants, and soils.

In a WUI fire, the burning of vegetation and buildings creates a more complex mixture of gases, particles, and harmful chemicals that can remain in outdoor air for days and weeks, and downwind inside buildings for considerably longer, posing health risks to occupants and cleanup workers.

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In downwind buildings impacted by smoke and heavy metals, there are similarities between lead dust and smoke combustion byproduct removal, but there are also distinct differences, such as:

• Lead dust is a more serious health hazard than wildfire smoke residue.
• The level of worker protection is generally much higher for lead dust than it is when removing wildfire smoke residue
• Lead dust generally settles on horizontal surfaces, where smoke impacts all surfaces
• Lead dust is invisible and has no odor, where smoke is a volatile organic and generally has an odor right after the fire, and feasibly weeks and months afterwards 
• The cleanup processes for lead dust are regulated, where smoke residue is not regulated
• The chemistry to remove lead is regulated, where smoke residue is not regulated
• Lead is inorganic requiring different processes to bind and chelate lead dust, where smoke is organic requiring different processes to chemically penetrate porous surfaces and dissolve and neutralize oils, tars, furans, and other combustion byproducts residues
• The post-remediation verification (PRV) testing for lead dust is regulated by EPA, where PRV testing involving the elimination of smoke residue is not regulated.

While the focus of the article is establishing the difference between organic combustion byproducts and inorganic lead dust, it is important to confer that lead dust in smoke impacted buildings is only one of the heavy metals that can produce toxic effects in humans, where it must be removed according to government regulations. After being brought into a home by a WUI fire, other heavy metals that are not regulated in “residential buildings”, but at certain levels they can be as toxic or carcinogenic as lead. Examples include arsenic, beryllium, cadmium, chromium, cobalt, copper, mercury, and nickel. When they are present at certain levels, the requirements for completing a job hazard assessment, establishing engineering controls, and worker protection are the same as for lead.

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Cal/OSHA T8 CCR §3380 (hazard assessment); T8 CCR §1532.1 and 5198 (lead); T8 CCR §3380 (dermal contact); T8 CCR §3382 (eye and face protection); T8 CCR §1528-1532.1 (contaminated work clothing); T8 CCR §3544 (respiratory protection)

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