Evaluating a
STRUCTURE FIRE
An IH Guide to Smoke’s Impact
BY MICHELLE ROSALES
Following a fire, property owners, insurance companies, and neighboring residents are looking for answers. What is damaged? Is it safe to return to my home? Are any of my belongings salvageable?
These questions can be difficult to answer, especially in cases where the fire is minor or where physical damage isn’t observed. IHs, using our knowledge about recognition and evaluation of hazards, can help answer these questions. However, assessing a structure fire is challenging even for IHs because few reference documents are available, and few methods exist for sampling and laboratory analysis.
This article provides general guidance on assessing the impact of a structure fire on properties and contents. The term “impact” refers to physical damage and the presence of surface contamination—for example, fire- and smoke-related particulates, or polychlorinated biphenyls (PCBs)—at the property. My purpose is not to outline a comprehensive assessment strategy for all types of structure fires and situations, nor will I provide guidance on evaluating environmental health risks or structural integrity issues following a fire. Each property and evaluation is unique and should be assessed based on project considerations and information provided.
Most structure fire consultants are retained by homeowners and insurance companies, specifically to help settle a dispute over smoke impact or to evaluate areas of concern that are not visually distinguishable. Preparation for assessment of a structure fire starts well before the site visit and begins with the gathering of background information. BACKGROUND Every thorough investigation begins with gathering as much background information as possible prior to arriving on site. Start by focusing on the “five W’s”: who, what, when, where, and why.
Who is requesting the assessment? A homeowner is typically concerned about the structure and its contents. Tenants might only be interested in their personal belongings. Identifying the stakeholders is the first step in developing an adequate assessment strategy. It’s important to consider that a structure fire might impact more than just the structure it started in: smoke infiltration can significantly affect neighboring structures and properties. Assessment strategies and sample locations may change based on the fire origin. For example, potentially affected neighboring structures may have different smoke pathways than structures with an internal point of origin.
What was the ignition source? The composition of smoke depends on the nature of the burning fuel—that is, the source—and the conditions of combustion. Structure fires typically involve the burning of materials such as plastics, electronics, and plaster that might produce a wide variety of hazardous compounds. Knowing what started the fire and what burned in the process will help you determine the appropriate sample and laboratory methods. For example, the burning of electronics can produce PCBs and various metal fumes, which can become airborne and eventually settle onto surfaces. Polycyclic aromatic hydrocarbons (PAHs) can be released into the air during cooking activities and during the burning of organic materials. Knowing what burned allows for the use of specific indicators to determine areas of potential impact without visible evidence.
When did the fire occur? Knowing when the fire occurred and how much time has passed between the fire and the on-site assessment will also help you determine the most appropriate sampling strategy. Will the indicators you selected based on what burned be appropriate and still remain on surfaces by the time you are there to assess? Have they volatized?

Where did the fire occur? Is the location industrial or residential? Is the place occupied for long periods of time? Are the occupants a sensitive population such as students at a school or patients at a healthcare facility? This would be an important question to ask when evaluating environmental health risk to occupants.

What is our scope of work? It’s unwise to form conclusions and recommendations when the purpose of the assessment is unknown. Are you there to determine impact to the structure? To evaluate contents or merchandise? To determine the environmental health risk to occupants prior to re-occupancy? Or to evaluate health and safety risks to remediation contractors?

Potentially affected neighboring structures may have different smoke pathways than structures with an internal point of origin.
ON-SITE INVESTIGATION A well-rounded structure fire investigation should include detailed sensory observations (for example, evaluating odors and assessing visible or physical impact), supplemented by sampling as needed.
Structure fires generally result in odors due to the burning of various manufactured materials. Although subjective, olfactory senses can be used during the evaluation to provide additional information on the degree of impact or potential pathways of smoke infiltration. Some materials generate a specific odor when burned. Most people are familiar with the smell of burning wood. The burning of plastic materials can produce a synthetic type of odor, which may present different contaminants (such as dioxins and styrene) that aren’t produced when organic wood materials are burned. Protein fires, which are caused by burning foods, can generate a repugnant smell with little visible impact.
Smoke impact should also be evaluated visually by surveying the property to identify areas of visible fire damage, fire- and smoke-related particulates, smoke staining, and corrosion.
Fire damage. The term “damage” is usually defined as the loss of appearance, utility, or value. This term may be deemed subjective by insurance companies and other stakeholders. For purposes of a typical IH structure fire assessment, “fire damage” can be defined as areas or items that have been visibly burned. In general, sampling of these items isn’t necessary unless the samples are being used as exemplars to determine whether areas without visible confirmation of impact have been affected (that is, on the microscopic level).
Fire- and smoke-related particulates. Fire- and smoke-related particulates are the most prevalent indicators following a fire event. These samples are easy to collect and analyze. Fire- and smoke-related particulates are categorized as char, ash, or soot:
  • Char is a partially burned piece of material that can be identified by morphology, color, relative opacity, fracture pattern, structure, and other characteristics.
  • Ash is the leftover residue following complete combustion.
  • Soot is a black carbonaceous substance produced during incomplete combustion.
Smoke staining. This refers to a black pigment generally observed in areas where thermophoresis results in the deposition of smoke-related particulate. Smoke staining can typically be found around picture frames, shelving, bed frames, and similar items. The hot smoke particles are transported along temperature gradients to areas of lower temperatures.
Corrosion. The corrosivity of smoke depends on the fuel source. Generally, corrosion is due to the creation of acidic gases and soot—both electrically conductive soot and electrically non-conductive soot. Corrosion by these mechanisms generally occurs within minutes to weeks and is typically associated with the burning of specific types of fuels such as plastic. If you’re assessing a property months after a fire event and don’t observe any corrosion, the likelihood that future corrosion will occur is minimal.
For assessing the impact to a structure from a fire, surface and bulk sampling are preferred over air sampling.
SAMPLING AND ANALYSIS It’s rare that a single method can be used to look for every analyte of concern in an air sample. This constraint holds true for surface sampling following structure fires. Again, obtaining the right background information prior to arriving on site will help determine the most appropriate sampling and laboratory methodology to use for the structure fire assessment. Selection of sample locations should be based on background information. In general, samples should be collected from representative surfaces needed to reach a conclusion on impact. These may be horizontal or vertical surfaces assessed with appropriate media.
For assessing the impact to a structure from a fire, surface and bulk sampling are preferred over air sampling. Each method has advantages and disadvantages.
Tape lifts involve collecting settled dust using a clear (transparent) tape affixed to a microscopic slide. This is the method of choice when analyzing for fire- and smoke-related particulates. Tape lifts provide something like a “snapshot” of conditions observed on site. The collected dust is not changed in any way prior to analysis. However, tape lifts can sample only small areas, making it difficult to draw larger-scale conclusions, and the analytical methods for tape lifts are limited. This method isn’t appropriate for porous surfaces and items.
Wipes collect settled dust using an absorbent material containing sterile alcohol over a certain area. Wipes can sample a larger area than tape lifts and have a greater range of analytical methods and analytes (for example, metals, VOCs, PAHs, and PCBs). But wipes can also alter the dust composition (it can be impacted by the alcohol), and the extraction of analytes is limited by the absorbent sampling material. Wipes are also not appropriate for porous surfaces and items.
Bulk sampling collects a piece of material for further analysis, such as a piece of a burned couch. This method allows for a larger sample size, and several pieces of material can be submitted for analysis. Bulk sampling materials are excellent choices for use as exemplars. The disadvantage of bulk sampling is that it limits what can be submitted to the lab, since property owners typically don’t want their belongings destroyed for analysis.
Vacuum/micro-vacuum sampling collects dust using a pump-and-filter collection system. It allows for collection of dust from porous, soft goods, as well as composite samples from larger areas. However, the extraction methods can alter the composition of the dust, and composite analysis leads to “averaging,” which can skew results.
Colorimetric strips can be used to determine acidity (pH) of the settled dust for assistance in corrosion evaluation. Collection via this method is easy, and laboratory analysis is inexpensive. For best results, the samples should be conducted shortly after a fire event. DATA ANALYSIS Interpretation of sample data for structure fires is often challenging due to the lack of evaluation criteria and reference documents. In addition, many analytes can be present at background levels in properties, which can confound interpretation.
For example, low levels of combustion-related particulates such as soot and PAHs are common in interior surface dust samples due to the presence of uncontrolled and controlled combustion within the property and the outdoor environment. Vehicle exhaust, wood burning, propane burning, industrial processes, candle burning, and natural gas burning are examples of everyday sources of combustion-related particulate. Therefore, surface dust commonly contains some background amount of fire- and smoke combustion-related particulate in typical residential and non-residential environments, regardless of a large fire event.
Most hygienists rely on their personal knowledge and experience from structure fire investigations when evaluating sample results. The resources listed below are among the published documents that provide reference levels for guidance in interpretation of samples. RECOMMENDATIONS Once impact has been identified and confirmed by either sensory observations or sample results, development of recommendations for restoration work is needed. For structure fires, the Restoration Industry Association (RIA) Guidelines for Fire & Smoke Damage Repair provides detailed guidance related to restoration of building materials and contents following a fire.
If cleaning practices as outlined in the RIA document are not enough to eliminate smoke odors, specialized odor removal techniques may be necessary. Primary odor removal should consist of removing or cleaning source materials. If the combustion particulate can’t be removed, the area may continue to emit odors. Other treatments such as thermofogging, oxidizers, counteractants (covering scents), and sealants (such as paints and encapsulants) may be used with discretion. The advantages and disadvantages of these methods should be investigated prior to recommending use. MICHELLE ROSALES, MPH, CIH, is a senior project manager of the Forensic Analytical Consulting Services, Inc. Los Angeles regional office. She can be reached at (310) 668-5617 or mrosales@forensicanalytical.com.
RESOURCES EPA, ATSDR and NY City Department of Health: World Trade Center Indoor Environment Assessment: Selecting Contaminants of Potential Concern and Setting Health-Based Benchmarks (PDF, May 2003). This document provides health-based benchmarks for various chemicals (for example, PAHs and dioxins) and metals in settled dust.
EPA: Polychlorinated Biphenyl (PCB) Site Revitalization Guidance under the Toxic Substances Control Act (TSCA) (PDF, November 2005).
EPA: Regional Screening Levels. This resource provides screening levels for various analytes identified in soils and air.
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Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers