RAG-KB/wildfire_soot_particulate_removal_full_text_extraction.md

SOOT PARTICLES: A Procedural Guide for Containing and Removing Wildfire-Caused Soot in Buildings

By Patrick J. Moffett, REA, CHMM Environmental Management & Engineering, Inc. Huntington Beach, California

Copyright © 1997, 2002, 2008 All Rights Reserved

SOOT PARTICLES: A Procedural Guide for Containing and Removing Wildfire-Caused Soot in Buildings

By Patrick J. Moffett, REA, CHMM Environmental Management & Engineering, Inc. Huntington Beach, California

Copyright © 1997, 2002, 2008 All Rights Reserved

COMMENTARY

The purpose of this paper is to provide a procedural guide for the restoration of buildings and contents contaminated with wildfire-caused soot. This paper was written primarily for restorers, insurance adjusters, and building owners who are dealing with extensive wildfire-caused soot contamination. This paper is not intended to be a comprehensive restoration manual for all smoke and soot contamination conditions. This paper focuses on wildfire-caused soot, ash, and odor contamination, and addresses worker and occupant safety and health issues; and in 2008, the paper was updated to address new concerns regarding ultrafine particles.

Worker Safety

In recent years, many restoration workers have been involved in cleaning wildfire-caused soot contamination. During these projects, workers often were observed wearing little or no respiratory protection. In some cases, workers were observed wearing simple dust masks or N95 respirators while performing soot cleaning activities. In other cases, workers were observed wearing N100 respirators or half-face respirators equipped with HEPA cartridges. In some cases, workers were observed wearing full-face respirators equipped with HEPA and organic vapor cartridges.

The question arises: What type of respiratory protection is appropriate for wildfire soot cleanup? In order to answer this question, it is important to understand the nature of wildfire-caused soot, including the size of the soot particles, the chemical composition of the soot, and the potential health hazards associated with exposure to soot.

PART I Particles and Chemicals in Smoke and Soot

Wildfire Smoke

Smoke is a complex mixture of gases and particles produced by the incomplete combustion of organic materials. Wildfire smoke contains numerous chemicals, including carbon monoxide, nitrogen oxides, hydrocarbons, aldehydes, ketones, alcohols, benzo[a]pyrene, and organic acids. The composition of wildfire smoke varies depending on the type of fuel burned, the combustion temperature, and the availability of oxygen.

Hot, flaming combustion tends to produce black smoke composed primarily of elemental carbon particles. Cooler, smoldering combustion tends to produce white or gray smoke composed of incompletely combusted organic materials.

Soot

Soot is composed primarily of carbon particles produced by incomplete combustion. Soot particles are often coated with organic chemicals, including polycyclic aromatic hydrocarbons (PAHs) and other combustion byproducts. The chemical composition of soot varies depending on the type of fuel burned.

Vegetation fires tend to produce gray or light-colored ash and soot composed primarily of inorganic ash and partially combusted organic materials. Fires involving petroleum products, plastics, roofing materials, and synthetic furnishings tend to produce black, oily soot composed primarily of carbon black.

Particle Size

Soot particles vary widely in size. Candle soot particles typically range from approximately 0.06 to 0.1 micrometers (µm) in diameter. Wildfire-caused soot particles may range from less than 0.1 µm to more than 30 µm in diameter. Larger particles, including embers, may be several inches in diameter.

Particle Deposition

Soot particles may be deposited on building surfaces by a variety of mechanisms, including gravity settling, impaction, diffusion, thermophoresis, and electrostatic attraction. Thermophoresis causes particles to move from warmer air toward cooler surfaces. Electrostatic attraction causes charged particles to be attracted to oppositely charged surfaces.

As a result of these mechanisms, soot often deposits preferentially on cooler surfaces, such as exterior walls, window frames, and surfaces near air leaks. Moist surfaces also tend to attract soot particles.

Firestorms and Convection

Large wildfires can generate intense convection currents, sometimes referred to as firestorms. These convection currents can create strong winds, dust devils, and fire whirls that carry smoke, ash, and soot over long distances. Buildings located near wildfires may be subjected to complex airflow patterns that influence the deposition of soot on interior and exterior surfaces.

PART II Environmental and Human Health Concerns

Chemical Composition

Soot typically contains approximately 60 percent carbon by weight. The remaining portion consists of a complex mixture of organic and inorganic chemicals, including PAHs and heavy metals such as arsenic, cadmium, chromium, and nickel. Thousands of individual compounds may be present in soot, many of which can be identified only by gas chromatography/mass spectrometry (GC/MS) analysis.

Health Hazards

Soot has been recognized as a human carcinogen. Occupational exposure to soot has been associated with an increased risk of skin cancer, lung cancer, and other health effects. Historically, chimney sweeps were known to suffer high rates of cancer due to soot exposure.

Workers involved in wildfire soot cleanup may be exposed to high concentrations of soot particles and associated chemicals. In some cases, these exposures may be comparable to or greater than those experienced by chimney sweeps and other workers historically exposed to soot.

Ultrafine Particles

In recent years, increased attention has been focused on ultrafine particles (particles smaller than 0.1 µm). Ultrafine particles are capable of penetrating deep into the lungs and entering the bloodstream. These particles may cause inflammation, oxidative stress, and other adverse health effects.

Wildfire smoke and soot contain large numbers of ultrafine particles. As a result, wildfire soot cleanup workers may be at risk of exposure to ultrafine particles unless appropriate respiratory protection is used.

Respiratory Protection

Respiratory protection for wildfire soot cleanup should be selected based on the size of the particles present and the presence of gaseous contaminants. Simple dust masks and N95 respirators are not adequate to protect against fine and ultrafine soot particles.

P100 respirators provide a minimum filtration efficiency of 99.97 percent for oil-based particles and are suitable for protection against fine and ultrafine soot particles. However, P100 particulate filters do not provide protection against gaseous contaminants such as carbon monoxide and organic vapors.

In situations where organic vapors or other gases are present, respirators equipped with both P100 particulate filters and organic vapor cartridges may be required. Full-face respirators provide additional protection for the eyes and face.

PART III Procedures for Removing Wildfire Soot from Contents

General Principles

The removal of wildfire-caused soot from contents should be approached systematically to minimize the spread of contamination and protect workers and occupants. Contents should be evaluated to determine whether they can be cleaned or must be discarded.

Dry Cleaning Methods

Dry cleaning methods are often preferred for removing soot from contents because they minimize the spread of contamination and reduce the risk of driving soot deeper into porous materials. Examples of dry cleaning methods include HEPA vacuuming, dry sponging, and the use of specialized dry cleaning compounds.

Wet Cleaning Methods

Wet cleaning methods may be used when dry methods are not effective. Wet cleaning should be performed carefully to avoid spreading contamination. Detergents and cleaning agents should be selected based on the type of material being cleaned and the nature of the soot.

Electronics

Electronics contaminated with wildfire soot require special handling. Soot particles can cause corrosion and electrical shorts. In many cases, electronics should be evaluated by qualified technicians and may require specialized cleaning or replacement.

PART IV Procedures for Removing Wildfire Soot from Buildings

Containment

Containment is critical to prevent the spread of soot during cleaning activities. Affected areas should be isolated using plastic sheeting and negative air pressure where feasible.

Surface Cleaning

Building surfaces should be cleaned using methods appropriate for the type of surface and the degree of contamination. Dry cleaning methods should be used whenever possible. Wet cleaning may be used when necessary, with care taken to avoid spreading soot.

HVAC Systems

Heating, ventilation, and air conditioning (HVAC) systems can become contaminated with wildfire soot. HVAC systems should be inspected and cleaned as necessary to prevent the redistribution of soot throughout the building.

Post-Cleaning Verification

After cleaning, surfaces should be inspected to verify that soot has been removed. In some cases, surface sampling or air monitoring may be used to confirm the effectiveness of cleaning.

Author

Patrick J. Moffett, REA, CHMM, is the principal of Environmental Management & Engineering, Inc., based in Huntington Beach, California. He has extensive experience in environmental health and safety, industrial hygiene, and hazardous materials management.

References

[References as listed in the original document]