Encyclopedia of Wildfires and Wildland-Urban Interface (WUI) Fires

Living Edition
| Editors: Samuel L. Manzello

Smoke Exposure

  • Fabienne ReisenEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-51727-8_126-1

Synonym

Definition

Smoke is a complex mixture of gases and particles that are emitted from the burning of substances, either natural or man-made.

Smoke contains a large number of chemicals that may cause short-term (acute) and/or long-term (chronic) health effects depending on exposure levels.

Smoke exposure assessment is the process of measuring or estimating the intensity, frequency, and duration of human exposure to a chemical present in smoke.

Introduction

Smoke is a complex mixture of chemicals unique to each fire in both its chemical composition and toxic features. Major combustion by-products produced during combustion of natural fuels include carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), particulate matter (PM) of various size distribution and chemical composition, volatile organic compounds (VOCs) including aldehydes, polycyclic aromatic hydrocarbons (PAHs), and other organic and inorganic compounds. At the wildland-urban interface, additional toxic gases are emitted due to burning buildings, vehicles, and other man-made materials. These include, for example, hydrogen cyanide (HCN), hydrogen chloride (HCl), hydrogen sulfide, ammonia, heavy metals, isocyanates, and other nitrogenated and chlorinated compounds.

The impact of a smoke plume on human health depends on the hazardous nature of the chemicals in the smoke plume as well as on the exposure intensity, frequency, and duration. Some chemicals in the smoke are likely to be a greater health concern because either they are hazardous or they are present in the air at concentrations to adversely impact on people’s health. The hazard from toxic chemicals can occur from acute exposure for even just a few seconds at very high concentrations and/or from chronic exposure at lower concentrations as a result of ongoing exposures. The risk of an adverse effect on health is proportional to hazard × exposure, i.e., the more hazardous a substance, the higher the risk. Likewise, for a given hazard, the greater the exposure, the greater the health risk.

Smoke Components Pertinent to Health

The key air toxics in smoke with the potential to cause adverse health effects include fine or respirable particles, CO, aldehydes (formaldehyde, acrolein, acetaldehyde), other VOCs (benzene, toluene, phenol), PAHs, other inorganic trace gases (nitrogen dioxide), and pollutant mixes (Naeher et al. 2007). The composition of smoke depends on the type of fuels burned and the combustion phase. During the rapid and intense flaming combustion, smoke composition is dominated by carbon dioxide and soot, while species such as CO, organic compounds, and higher particle concentrations are associated with the slow and prolonged smoldering combustion.

Particulate matter (solid or liquid particles suspended in air) is directly emitted from fires and can account for up to 3% of the burned biomass. Fires produce mainly fine particles less than 1 μm diameter which persist in the atmosphere for many days, increasing the likelihood of exposure. Fine particles have a large surface area-to-mass ratio meaning that a larger amount of contaminants can be absorbed to fine particles. Particles emitted from fires are mainly composed of carbonaceous materials (e.g., organic components and soot) with a small contribution from inorganic species (e.g., nitrate, sulfate, ammonium, and chloride) (Reid et al. 2005; Capes et al. 2008; Vakkari et al. 2014). The differences in the particle size and composition depend on the type of fuels burned and combustion phase (e.g., flaming or smoldering). Particle size and composition define where the particles deposit in the lungs and what sort of toxic effect they can exert.

CO, a colorless and odorless gas, is produced during incomplete combustion of biomass. Elevated concentrations of CO have been measured on the fire line, indicating that firefighters can be exposed to hazardous concentrations of CO (Reinhardt and Ottmar 2004; Reisen and Brown 2009; Miranda et al. 2010; Reisen et al. 2011). Combustion experiments under controlled conditions have shown that the highest ratio of CO production was measured under smoldering conditions immediately after cessation of the flaming phase.

A range of volatile and semi-volatile organic compounds are released during fires. VOCs include benzene, toluene, xylenes, and aldehydes, with formaldehyde being the most abundant aldehyde produced during forest fires (Reinhardt and Ottmar 2004; Reisen and Brown 2009); semi-volatiles (SVOC) include phenolic compounds that are produced from the oxidation of cellulosic fuels. While benzene and other hydrocarbons are a product of combustion of forest fuels, they can also be emitted from drip torches and engine-operated equipment such as pumps or chainsaws.

At the wildland-urban interface, burning buildings are likely to change both the composition and concentration of emissions. The presence of nitrogen-rich materials such as wool, nylon, and polyurethane releases HCN, ammonia, nitriles, and other nitrogenated organic compounds, while combustion of polyvinylchloride (PVC) releases HCl and other chlorinated organic compounds. Previous studies conducted at structural fires have found air pollutants of concern to be CO, formaldehyde, acrolein, HCl, HCN, hydrogen sulfide, hydrogen fluoride, benzene, nitrogen dioxide, sulfur dioxide, and PAHs (Brandt-Rauf et al. 1988; Jankovic et al. 1991; Bolstad-Johnson et al. 2000; Austin et al. 2001).

Acute Health Effects Resulting from Firefighters’ Exposure to Smoke

Acute health effects generally result from a brief exposure to high concentrations of a toxic chemical. Short-term exposure limits and peak limits are set by safe workplace standards for a range of rapidly acting substances and irritants to minimize acute health impacts. Emergency situations like fires and accidents can lead to acute exposures at uncommonly high concentrations. The following section highlights some of the acute adverse health impacts that can result from exposure to smoke.

Disruption to Oxygen Transport

Hypoxia occurs when not enough oxygen is supplied to the tissues and organs in the body, and under severe conditions this can cause coma or death. CO and HCN, labeled the toxic twins, are chemicals that affect oxygen transport, availability, and utilization to tissues in the body. CO and HCN toxicity mainly targets organs with a high demand for oxygen, particularly the brain and heart. HCN is more dangerous than CO (Simeonova and Fishbein 2004). HCN acts by inhibiting cytochrome oxidase, which prevents cellular utilization of oxygen.

When CO is inhaled, it competes with oxygen for binding sites on hemoglobin, the oxygen-transport protein in the red blood cells that carries oxygen from the lungs to the rest of the body (e.g., brain, muscles). CO binds to hemoglobin between 210 and 240 times more strongly than oxygen and produces carboxyhemoglobin (COHb). The amount of COHb formed depends on the CO concentration in the air, the duration of exposure to CO, and breathing rate. COHb has a half-life of about 4–6 h, and COHb levels will return to background levels once CO exposures are eliminated. Purging CO from the body can take 18–24 h. Therefore people should be mindful when having a continuous exposure to CO over several days. In order to minimize potential symptoms from overexposure to CO, it is recommended to keep COHb levels below 5%. As an example, 5% COHb is reached when being exposed to 30 ppm CO averaged over an 8-h period while sedentary or to 100 ppm CO for 40 min under a light workload.

The oxygen deprivation in the body may cause headaches, tiredness and dizziness, cognitive impairment (e.g., effects on visual perception, vigilance, hearing, and motor functions), decreased exercise performance, and, in extreme cases, unconsciousness. At higher concentrations, it can lead to severe headaches, nausea, mental confusion, and unconsciousness (WHO 1999). Table 1 lists some of the symptoms/effects that are observed at various COHb levels, with the risk for CO-induced symptoms varying substantially between individuals. People with underlying heart and lung disease are at greater risk as they will have little tolerance to even mild hypoxia.
Table 1

Symptoms and health effects with various levels of COHb (World Health Organization (WHO) 1999)

COHb [%]

Symptoms, effects

0.3–0.7

Normal endogenous level

5

Potential for adverse cardiovascular effects, decrease in short-term maximal exercise duration

5–10

Effects on performance of tasks requiring vigilance and on reaction time, potential headaches, dizziness, reduced work capacity

10–20

Slight headaches, dizziness, possibly slight breathlessness on exertion, impaired ability to perform tasks

20–30

Slight to moderate headaches, nausea, raised pulse rate, dulling of the senses

30–40

Severe headaches, vertigo, nausea, vomiting, weakness, exertion may lead to faintness

40–60

Weakness and decreased coordination, mental confusion, memory failure

>60

Unconsciousness, convulsions

Irritation to Eyes, Nose, Throat, and Upper and Lower Respiratory System

A wide range of smoke components can cause irritation to the eyes, nose, throat, and respiratory system and potentially lead to breathing difficulty and exacerbation of pre-existing respiratory conditions. Compounds within this class include fine particles, aldehydes, VOCs, nitrogen dioxide, ammonia, hydrogen chloride, sulfur dioxide, and isocyanates.

Due to their small size, particles can easily reach the alveolar region of the lungs, where clearance is slow and the potential for adverse health effects is high. Fine particles increase airway resistance; cause irritation, coughing, and difficulty breathing; and aggravate asthma. Acute exposures to high particle levels can trigger asthma attacks and may increase susceptibility to respiratory infections or lead to lung dysfunction.

A number of VOCs, including aliphatic and aromatic hydrocarbons, aldehydes, ketones, and acids, are respiratory irritants that reduce ciliary activity. In the lungs this reduces the efficient removal of particles and microorganisms from the respiratory tract. Formaldehyde causes upper respiratory irritation at levels exceeding 1.2 mg/m3 (Dost 1991). Acrolein causes irritation at levels as low as 0.23 mg/m3 and is a more potent irritant than formaldehyde (Beauchamp et al. 1985). Although mostly present at lower concentrations than formaldehyde, acrolein may contribute significantly to the irritant effects caused by smoke. It is also suggested that inhalation of PAHs can cause airway inflammation.

Ammonia and HCl can cause intense and prolonged inflammatory reactions. Nitrogen dioxide is a highly acid irritant that can cause fluid accumulation and may cause respiratory failure. Sulfur dioxide is highly irritating to the eyes and respiratory tract. Isocyanates are powerful irritants to the mucous membranes of the eyes and gastrointestinal and respiratory tracts and can aggravate respiratory conditions, trigger severe asthma attacks in susceptible people, and cause shortness of breath, wheezing, and chest tightness.

Cardiovascular Effects

Particles, carbon monoxide and nitrogen dioxide, can aggravate pre-existing heart conditions. Short-term exposures to elevated levels of fine particles can cause heart attacks and arrhythmias in people with heart disease. As carbon monoxide competes with oxygen for binding sites on hemoglobin in the blood, it reduces the oxygen-carrying capacity of the blood. To compensate for the reduced oxygen delivery, the heart works harder and beats more frequently. Therefore people with underlying heart disease are at greater risk for CO ill effects.

Effects on the Central Nervous System

Most common symptoms include headaches, nausea, dizziness, fatigue, confusion, and loss of coordination or judgment. Some of the compounds present in smoke that affect the central nervous system include CO, ethylbenzene, toluene, styrene, xylenes, alkanes, phenol, and hydrogen sulfide. In general the symptoms disappear once exposure stops.

The most likely health effects experienced by firefighters are eye, nose, and throat irritation, headaches, and wheezing (in particular for asthmatics). In more severe cases of exposure to heavy smoke, firefighters may experience nausea and dizziness. The common health effects from exposure to smoke are summarized in Table 2. While most of the symptoms and health effects are transitory, exposure to smoke can affect work performance, and for ongoing exposures acute health effects may lead to chronic health effects.
Table 2

Compounds grouped by primary target organs for acute health effects and cancer

Compound

Eye irritation

Respiratory tract irritation

Skin irritation

Impaired lung function

Exacerbation of respiratory illnesses

Exacerbation of cardiac illnesses

Impact on central nervous system

Hypoxia

Carcinogena

Fine or respirable particles

x

x

 

x

x

x

x

 

Group 1

Carbon monoxide

     

x

x

x

 

Ammonia

x

x

x

x

x

    

Hydrogen chloride

x

x

  

x

    

Hydrogen cyanide

 

x

    

x

x

 

Hydrogen sulfide

x

x

    

x

x

 

Nitrogen dioxide

x

x

 

x

x

x

   

Ozone

 

x

 

x

x

    

Sulfur dioxide

x

x

 

x

x

 

x

  

Acetaldehyde

x

x

x

 

x

 

x

 

Group 2B

Acetic acid

x

 

x

      

Acrolein

x

x

  

x

   

Group 3

Benzene

x

x

x

   

x

 

Group 1

1,3-Butadiene

        

Group 1

Ethylbenzene

x

x

    

x

 

Group 2B

Formaldehyde

x

x

x

 

x

   

Group 1

Isocyanates

 

x

      

Group 2B

Phenol

x

x

       

PAHs

x

x

      

Group 2B

Styrene

x

x

    

x

 

Group 2B

Toluene

      

x

  

Xylenes

 

x

    

x

  

aClassification according to the International Agency for Research on Cancer (IARC): Group 1, carcinogenic to humans; group 2B, possible carcinogenic to humans; group 3, not classifiable as to its carcinogenicity to humans

Chronic Health Effects of Firefighters’ Exposure to Smoke

Chronic health effects are characterized by prolonged or repeated exposures over many days, months, or years, and symptoms may not be immediately apparent. Chronic adverse health impacts that can result from exposure to smoke include lung damage, heart disease, chronic bronchitis, and cancer. The risk for long-term health effects depends upon the magnitude and frequency of exposure, the duration of exposure (in years), exposure to other pollutant sources (e.g., vehicle exhaust, cigarette smoking), and the health status of the individual.

Exposure to smoke containing high concentrations of formaldehyde, acrolein, acetaldehyde, and particles may lead to chronic respiratory health effects. Exposure to acrolein is likely to present the greatest health risk despite it being present at lower concentrations. This is due to its higher irritant potency.

Compounds emitted from fires that are carcinogenic to humans include benzene, formaldehyde, and benzo(a)pyrene. Benzene has been linked to leukemia; formaldehyde has been classified as a known human nasal carcinogen (IARC 2004a, 2012). Recently, the International Agency for Research on Cancer (IARC) has also classified PM and outdoor air pollution as carcinogenic to humans. About 40–70% of the fine particles consist of organic materials, and many carcinogenic compounds such as PAHs are contained within this fraction. These harmful adsorbed contaminants may be delivered deeper into the lung tissue.

Other compounds such as acetaldehyde, ethylbenzene, naphthalene, styrene, and isocyanates are possibly carcinogenic to humans.

Cumulative Health Effects Due to Smoke Exposure

For exposures to individual air toxics, there is unacceptable level of exposure risk if the hazard quotient, e.g., the ratio between the exposure concentration and the respective occupational exposure standards, is greater than 1. In a smoke plume, a number of air pollutants are present in varying concentrations. To assess potential health impacts for a mixture of pollutants targeting the same organ, e.g., irritation to eyes or respiratory tract, hazard indices are used. A hazard index is the sum of hazard quotients of all air toxics with similar effects that a person is exposed to. Any hazard index exceeding unity represents an unacceptable level of exposure risk.

Examples of additive effects due to exposure to mixture of chemicals are CO and HCN, both asphyxiants as well as the wide range of irritants in smoke plumes (e.g., PM, acrolein, formaldehyde, HCl, VOCs). If exposed to one pollutant, concentrations may not be high enough to cause irritation. However, exposure to a mix of pollutants may aggravate conditions.

Synergistic effects occur when one chemical enhances the toxicity of another chemical. These are much more difficult to assess. For example, smoking has a synergistic effect in combination with inhaled particles from other sources, while CO can increase the respiratory intake of other gases in the smoke by stimulating the respiratory center in the brain.

Heavy workload can also exacerbate health effects. This is due to increased intake of air and hence increased intake of pollutants. Furthermore when breathing harder, pollutants are carried deeper into the respiratory tract where clearance is slow. During heavy breathing, a larger fraction of air is also inhaled through the mouth, thereby bypassing the normal nasal filtration.

Adverse climatic conditions such as excessive humidity or heat or work at high altitudes may also cause an increased uptake of contaminants.

Health Effects of Community Exposure to Smoke

Smoke emitted into the atmosphere can be transported downwind and impact on communities. The major pollutant of concern in fire plumes impacting communities is PM, which consistently exceeds air quality guidelines. Particles can be transported over long distances and impact on communities that are hundreds to thousands of kilometers away from a fire. Major health effects on populations that have been linked to exposures to elevated levels of PM in smoke include respiratory symptoms and illnesses such as coughing, wheezing, shortness of breath, asthma attacks, and exacerbations of other pre-existing respiratory conditions. Cardiovascular effects from exposure to high levels of particles are less conclusive.

Ozone, which is formed in smoke plumes during transport, may pose a potential health risk, in particular during warmer months in urban areas with elevated background ozone concentrations. Exposures to high concentrations of ozone can lead to reduced lung function and lung inflammation even in young and healthy individuals (WHO 2006).

Because most of the air toxics in smoke impact the respiratory and cardiovascular system, people that are more susceptible to ill effects from smoke include the elderly, young children, asthmatics, and people with pre-existing respiratory and/or heart conditions.

Cross-References

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.CSIRO Oceans & Atmosphere, Private Bag 1AspendaleAustralia

Section editors and affiliations

  • Pedro Reszka
    • 1
  1. 1.Universidad Adolfo IbañezSantiagoChile