Introduction

As our planet is getting warmer rivers, lakes, large watersheds are drying up every year, and more wildfires are becoming increasingly common throughout the world. These wildfires take in the form of large and uncontrolled burn of natural vegetation and may continue to burn for weeks or months. The effects of wild fire can be devastating including loss of ecosystem and diversity, forest and soil degradation, air pollution, economic losses, destruction of watersheds, impact to human well-being such as loss of lives and complete destruction of villages and towns.

California is especially prone to wildfires because of unprecedented drought for the last decade and heat exacerbated by climate change, overgrown forests caused by decades of fire suppression, and rapid population growth along the edges of forests. The state is known for its wildfire seasons, which usually take place between late spring and autumn, but they are getting increasingly more intense, destructive, and longer in the past two decades. At least a third of some of the worst wildfires in US history occurred in California. Data from the Western Regional Climate Center shows that the northern two-thirds of the state received only half of normal rainfall over the past few years. The U.S. Drought Monitor has categorized about 85 to 90 percent of California is experiencing extreme or exceptional drought for all of summer 2021. According to data from the National Centers for Environmental Information, the period between September 2019 and August 2021 ranked as the second-driest on record for the state. Enormous wildfires have been constantly raging in California in recent summers. According to the California Department of Forestry and Fire Protection, eight of the state’s ten largest fires on record—and twelve of the top twenty—have happened within the past five years. Together, those twelve fires have burned about 4 percent of California’s total area.

Constituents of wildfires and their effects on human health

Wildfire smoke contains combustion by-products, which are gases and small particles generated when materials burn. These combustion by-products include ash, soot and char particles and can travel several miles away from the origin of fire. Wildfire smoke, often times coming from several miles away, can be carried into a home. There are multiple pathways for smoke to enter a home including vents, chimneys, and openings around windows and doors. A home that is affected by a wildfire evacuation is particularly at risk for smoke intrusion because the owners often leave at a moment’s notice due to safety reasons, potentially leaving windows open. The main combustion by-products are ash, char, and soot.

Ash is pyrolyzed material obtained from advanced combustion of char particle that is left when a substance is burned. Ash includes trees and vegetation but can also include building material or any other burned object. Because the carbon matrix of char particle is almost completely combusted, ash is mainly inorganic with a high amount of calcium, potassium, magnesium, aluminum, silicon, phosphorus or sulfur. The ash particles are very brittle and may or may not contain some of the original material’s cell structure. Ash has high pH (9 to 11). The abrasive particles of ash can scratch the surface of the skin and eyes, causing discomfort and inflammation. If inhaled, ash can cause breathing problems and damage the lungs. Inhaling large amounts of ash can cause a person to suffocate.

Char is often associated with remnants of burnt wood and damaged building materials. Char particles are produced when a substance or material does not completely burn and is a incomplete combustion by-product. The size of the char particles can range from 1 to 500 micron. It is darker than ash and can range up to several millimeters in size. Char particulate may not de-agglomerate or disperse by ordinary techniques, may contain material which is not black, and may contain some of the original material’s cell structure, minerals, and ash. Carbon is typically the predominant component in char particle. The reviewed literature suggested that the respiratory effects of char particle and inhaling for longer period may cause chronic obstructive pulmonary and cardiovascular diseases. In addition, char particles are also known to be carcinogenic to humans.

Soot is frequently referred to as carbon black because of the color, but soot is not carbon black. Carbon black (also known as acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion coal and coal tar, vegetable matter, and petroleum products. Carbon black is a distinct material that is commercially produced under highly controlled conditions and is used extensively as an ingredient used to strengthen rubber in tires, but can also act as a pigment, UV stabilizer, and conductive or insulating agent in a variety of rubber, plastic, ink and coating applications.

Soot, on the other hand, is sub-micron black powder generally produced by-product of combustion or pyrolysis of vegetation. Soot consists of varying amounts of carbon and inorganic solids in conjunction with adsorbed and occluded organic tars and resins. Soot contains acids, chemicals, metals, soils, and dust. These particles leave a black stain and foul smell. During a fire, soot spreads to the whole house, and attaching to surfaces. Thus, the acidic properties of soot can further affect the property and indoor air quality if the soot is not removed immediately.

Soot can be found in the home even if there was not a fire. For example, excessive use of candles can lead to soot buildup. Thus, property owners should not use them quite often since they may also pose a fire risk. Fireplaces can release soot, as well, if they’re not properly ventilated. Furnaces are also a source of soot contamination when they produce a puff back. Soot can enter the body through inhalation, ingestion or via the skin and eyes. Epidemiological studies have shown that significant association between human exposure to soot and adverse health effects which include exacerbation of underlying pulmonary and cardiac problem that can lead to earlier death of increased morbidity. Long term effects may include cancer, asthma, lung disease and heart diseases. To avoid the health risks of soot exposure after a home fire, all soot-affected areas in the property must be properly cleaned and sanitized.

Insurance for wildfires

Smoke damage can be costly and hard to get rid of. Smoke is very invasive it is difficult for a homeowner to clean and repair smoke damage. Special tools and equipment are typically required. And there are also safety considerations the home owners need to be aware of. Many homes contain asbestos and lead-based paint. If left undisturbed these are typically not hazardous. However, during a fire microscopic asbestos fibers and lead particles might be released into the air. It is important to hire a professional industrial hygienist to test for asbestos and lead. Based on their recommendations, home owners might have to hire an asbestos abatement contractor or lead remediation contractor. Homeowners need to remove smoke particles and need to use a professional fire restoration company to clean and decontaminate the home.

It is important for homeowners to protect financially by having adequate fire insurance in the event of a wildfire. While every insurance policy is different, a standard homeowner’s insurance policy typically covers all interior and exterior smoke damage. It is important to review insurance policy to ascertain exact coverage. The homeowners should take prompt action if home is damaged by wildfire smoke and take the following actions:

Insurance provider should be immediately contacted. Time is of the essence as smoke damage can become permanent if left too long on items that would otherwise be able to be cleaned.

Homeowners should examine the policy’s declaration page and see how much the deductible is.

Without disturbing the scene, homeowners should take photos and video so that it can provide proof if anything is in question later.

Homeowners should get a smoke damage testing and remediation estimate.

While smoke damage is still fresh, homeowners should write down the date and time of the loss, where it originated and what became damaged, the property owner’s information if rented, contact information, a copy of the police report, and any estimates that can provide to the insurance company. By providing as complete a profile as possible, the adjuster can proceed with the claim in a timely fashion. It is important to know that insurance adjusters always look after the best interests of insurance company.

Repairs should return homes to the uniform and consistent appearance even if it means replacing partially undamaged items such as flooring. Insurance companies will often pressure homeowners to accept similar looking products instead. It is good idea to consult a lawyer if insurance company denied the claim. Also hiring a public adjuster can help. A public adjuster looks after homeowners’ interest, not the best interest of insurance company.

Sample collection

The best way to demonstrate the smoke damage in a home and on property is to test for their presence. Both surfaces and the air inside a building can be tested for combustible by-products. Testing should be performed, whenever possible, by a professional industrial hygienist. It is important for an industrial hygienist to locate and test in all areas of potential smoke entry. Homeowners will often hire their own industrial hygienist. They are required to perform mass testing after a wildfire, requiring to test multiple homes in an area in a short period of time. This predictably leads to sloppy testing and a failure to locate the areas of a home most at risk.

Sometimes industrial hygienists avoid testing areas of a home where the most combustible by-products are present. If homeowners do not retain their own hygienist, insurance company will often use its certified industrial hygienist’s (CIH) inadequate testing as a basis to deny any smoke damage that is present inside the house.

When a hygienist goes for inspection and collection of samples from wildfire damages, visual inspection is the most important aspect of investigation. Hygienists can easily identify dark-colored particle after the occurrence of fresh wildfire. It is important that hygienist should record presence of any heat or smoke damage, smoke odors, how dark-colored particles different from other environmental or combustion products or dust, if combustion products are gathered in the interior and exterior spaces and surfaces, structural ledges, flooring, baseboards, attic spaces, garages, window sills, furniture, paintings, and decorative objectives. The hygienist should take enough photographs and videos to document the damages or presence of combustion products both inside and outside of the property. These information are necessary for processing insurance claim.

Samples are collected from the affected areas using 3 different sampling technique and media:

Wipe: A wipe is a small piece of colorless, non-fragranced cellulose material used to collect samples. Wiping an affected area is used to collect the particles, however, this technique will not collect smaller particles and in on-porous areas. In addition, wet wiping will solubilize and create a muddy layer if area is heavily laden with particles and leaves a black stain on the surface. In our opinion, wiping is not a good sampling technique. Wipe samples can destroy the physical integrity, size distribution, spatial distribution, dissolve ash components and aciniform of soot particles, making difficult for the laboratory to identify these particles.

Micro vacuuming: Vacuum is used to collect the surface sample as wells as carpet sample. Vacuuming creates low pressure and draws air into the vacuum chamber. The force of the air may destroy the integrity of ash and soot particle and we do not recommend vacuum to collect the sample.

Tape: Tape lift sampling is a preferred method for collecting surface sample since it preserves the positions and integrity of all the particles on the original surface. Samples are collected using adhesive clear tape (not frosted tape), placed on the surface to be sampled, lightly pressed to collect the particles, and are removed. Tape lift can collect ash as well as other fragile particles and remain intact in the adhesive side of the tape. We recommend using tape to collect the samples since tape lift can retain the particle morphology, spatial distribution, and chemical nature of the particle.

Air sample: Air samples for both outdoor and indoor environments can be collected using air sampler. The air passes through a collection device (cassettes) which catches air-borne particulate in a filter paper. In our opinion, this is not a good sampling procedure since sampling time delay, particles may have settled on the floor, and sir sampler may not catch heavier particle such as char.

According to Kovar et al (2016) and Crutcher et al (2017), the efficiency for collecting sample by tape lift is about 95 to 98 %, wipe is 75% and for vacuum is about 20%.

Wildfire residue analysis

Several methods have been developed for assessing fire particulates including IESO/RIA Standard 6001-2012 (Evaluation of Heating, Ventilation and Air Conditioning [HVAC] Interior Surfaces to Determine the Presence of Fire-Related Particulate as a Result of a Fire in a Structure), ASTM D1506-15 (Standard Test Methods for Carbon Black-Ash Content), and ASTM D6602-13 (Standard Practice for Sampling and Testing of Possible Carbon Black Fugitive Emissions or Other Environmental Particulate, or Both). The samples collected from wildfire debris contain complex mixtures of unburned particles, fully combusted particles, and partially burned particles. Partially burned particles are semi-volatile, semi-soluble and fragile. These samples can be destroyed during sample collection, laboratory sample preparation and analysis. Some aspects of wildfire contamination are not suitable for analyses of post-fire samples as described above and have their own limitation. Therefore, it is often necessary to go beyond these methods for applicable information.

The wildfires particles are identified at the laboratory using scanning electron microscopy (SEM), transmission electron microscope (TEM) and optical microscopy (OP).

During SEM and TEM sample preparation, partially burned materials that are physically fragile, semi-volatile, or semi-soluble can be altered or destroyed. In the past, these limitations have caused significant confusion while analyzing wildfire particles using electron microscopes. TEM is often suggested to identify the individual submicron aciniform soot particles, however, the reliability of this procedure for carbonaceous particles other than carbon black. Besides, soot particles can dissolve in the solvents during TEM preparation and evaporate when placed under the high vacuum used in the TEM analysis process. These losses can be significant, especially with low-temperature, smoldering fires. As a result, ASTM 6602 method to assess the lower temperature and uncontrolled residues found in the wildfire will produce unreliable results.

OP using polarized and reflected light microscopy is one of the most useful methods since it can provide information on several levels. OP can be used to identify soot, char, and ash, as well as as plant phytoliths, burned pollen grains, and burned soil clay particles. The proportion of fire residue particles to biological and inorganic particles provides an estimate of the percentage of fire to non-fire particles. The levels approximately 5 percent likely indicate an increasing probability of fire residue contamination.

Besides OP, ash particles can also be identified using pH meter. Common dust has a pH 6 to 8 whereas concentrated fire ash has a pH 9 to 13.

Remediation or Cleanup

The contaminated houses need to be thoroughly cleaned so that inhabitants of the houses are not inhaling toxic combustion by products, feel safe, and the houses are returned as closely as possible to their pre-damage state. After thorough investigation and based on the laboratory analytical reports, industrial hygienists will prepare a remediation protocol. It is highly recommended that homeowners hire a professional fire restoration company to clean and decontaminate the contaminated homes. A remediation company will follow several procedures such as removal of loose combustion particles using HEPA vacuum from the affected areas, thorough cleaning of porous and non-porous materials, clean HVAC, duct, ventilation system, and replace air filters. If necessary, remediation company will set up containment units and run negative air filtration vacuums. These high-efficiency particulate air (HEPA) vacuums are very effective in clearing particulates and deodorizing affected home.

The remediation company will also clean exterior of the house such as swimming pool (if any), decks, siding, driveways, concrete railings, etc. Another important aspect is to remove smoke odors. Remediation companies use many commercial products and devices to remove the smoke odors.

Post Remediation Clearance

It is important to do a post remediation clearance test so that homeowners know their homes are cleaned, toxic combustion by products as well as smoke odors are removed, and their houses are returned to pre-damage state.

Particles are a surface and dust contamination concern. A thorough cleaning of the surfaces and removal of dust may take care of the majority of particulate contamination. However, the biggest problem with particulate contamination is the possibility of recontamination, especially in an extensive wildfire situation in which char, ash, and soot from the fire remains in the outdoor environment, and air movement as well as foot traffic can bring the fire residues back into the building.

Conclusion

Wildfires are becoming more and more frequent as our earth is getting warmer. Wildfire smoke contains combustion by-products, which are gases and small particles generated when materials burn. These combustion by-products include ash, soot and char particles and can travel more than 50 miles from the origin of fire and can contaminate homes. Ash, char and soot particulates can have adverse health effect such as cancer, pulmonary and cardiovascular diseases, To avoid the health risks of combustion by-products exposure after a wild fire, all the affected areas in the property must be properly cleaned and sanitized. Most of the fire insurance policies cover all interior and exterior smoke damage. Homeowners should hire professional industrial hygienists to assess the damage, collect the samples from the affected areas. The industrial hygienist will generate a report and write a remediation protocol based on his or her own investigation and laboratory analytical reports. After remediation it is important to do a post remediation clearance to make sure houses are returned as closely as possible to their pre-damage state.