Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Smoke from Wildfires

AIRNOW is a cross-agency U.S. government website devoted to air quality and its impact upon human health. The fire season has begun with a vengeance in California, with approximately 1100 fires burning today. Because of the tremendous number of wildfires burning in California, an unprecedented portion of the state is suffering hazy, smoke-laden air. Utilizing information from AIRNOW and other sources, including the American Lung Association and Environmental Protection Agency, here is a brief overview of important considerations related to what will undoubtedly be a very active fire season.

First and foremost, smoke from fires can affect your health. A person does not acclimate to smoke in any way, and repeated exposures can diminish lung function. So, avoidance is very important.

The discussion of intense exposure to heat and smoke when in the immediate proximity of a raging forest fire is a separate topic, because there are considerations of becoming burned, asphyxiated from lack of oxygen, affected by carbon monoxide, and injured by other severe, acute causations. The focus of what follows is exposure to smoke exposure of a degree to create a hazy horizon, where you can see, smell, and taste the smoke, and must make a decision to what extent, if any, you should modify your behavior and activities.

Healthy persons are usually not at a major risk from such smoke. But of course, it's always a good idea to avoid breathing smoke if you can help it. Smoke is not good for you.

Smoke is a mixture of gases and fine particles produced when wood and other organic matter burn. It reflects the fuel, so can contain products of combustion from rubber, plastics, and any other material consumed in the blaze. Firefighters have the greatest exposures to smoke, and they are often affected. It has been estimated that nearly 40 to 50% of medical encounters by wildland firefighters are for respiratory problems. Whether or not this statistic can be perfectly extrapolated to a non-firefighter population passively exposed to wildfire-generated smoke is not known, but it is highly likely that respiratory ailments and diminished lung function would be a logical result of exposure to smoke.

What's in the smoke. Some of the combustion products of concern include these classes of materials: particulate matter (organic and inorganic), carbon monoxide, ozone, organic acids, polynuclear aromatic hydrocarbons, volatile and semi-volatile organic compounds, and free radicals. These are present or absent in varying degrees depending on the fuel burned, temperature of the fire, suppression method(s) used, and other factors. Therefore, the toxicity of the smoke may vary, but for the purposes of this discussion, all smoke from wildland fires should be considered comparable.

Because particulate matter dominates in proportion within wildland fire smoke, the greatest health threat from smoke comes from the fine particles, which are often microscopic. The particles easily get into the eyes and respiratory system, where they can cause health problems such as burning eyes (conjunctivitis), irritated throat, runny nose (sometimes associated with an allergic response), and illnesses such as bronchitis (cough). Fine particles also can worsen chronic heart and lung diseases. Because death rates from these conditions have been noted to rise in a smoky environment, the smoke has been linked to premature deaths in people with these conditions, in a fashion analogous to increased mortality during heat waves.

Persons who are more susceptible to ill effects at lower smoke levels are those heart disease (congestive heart failure, symptomatic angina, cardiomyopathy), lung disease (asthma, reactive airway disease, chronic obstructive pulmonary disease [COPD]), and any medical condition in which oxygen delivery and heart and lung function are essential for health and wellness.

Older adults appear to be at increased risk of being affected by smoke, as do children with high activity levels. Firefighters, athletes, soldiers, and others who exercise in smoky conditions often report feeling poorly, sometimes up to the point of incapacitation.

It is not difficult to know if smoke is affecting you, if you develop symptoms. It is less easy to know if you are being affected if the impact is subtle. Obvious symptoms are irritated and reddened eyes; painful throat; fatigue; decreased exercise tolerance; palpitations; chest pain; shortness of breath or inability to draw a deep breath; coughing; wheezing; sinus irriation; headache; or worsening of pre-existing conditions that manifest any of these symptoms.

Prevention is key. One must know how to limit exposure to smoke:

Pay attention to local air quality reports, and to the Environmental Protection Agency's Air Quality Index (AQI)(more about this below). Stay alert for any news coverage or health warnings related to smoke. You can check out news on current status of wildfires by going to the website

Use visibility guides, if they're available. Not every community has a monitor that measures particle levels in the air. In the western United States, some areas without air quality monitors have developed guidelines to help people estimate the AQI based on how far they can see.

Common sense is the cornerstone of everything we do in wilderness medicine. If it's smoky outside, do not plan to exert yourself. Do not run the race and consider keeping your children indoors. If you develop smoke-related symptoms, curtail any contributing activities and seek an environment away from the smoke. Ordinary dust masks are designed to filter out large particles, so do not count on them to diminish exposure to small particulate matter found in smoke.

The air indoors is also important during times of high smoke levels outdoors. So, you should keep indoor air as clean as possible. Unless it is extremely hot outside and you need to open windows and doors for air circulation, you should keep them closed. If you have an air conditioner, allow it to run, with the fresh air intake closed and the filter clean. Certain air cleaners might decrease particulate matter indoors, but be certain that the device does not emit ozone. Do not vacuum or smoke tobacco products, and do not burn anything that will emit smoke. If it becomes too hot inside a building or enclosure, find a cooler shelter, so that you are not overcome by the heat. When driving a car in smoky areas, keep the windows and vents closed.


The AQI (see the color chart above) is an index for reporting daily air quality that indicates how clean or polluted is the air, and what associated health effects might be of concern. The EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in the U.S. In the setting of smoke from a wildland fire, it is the particulate matter that is of greatest concern.

The AQI is reported as a numerical rating that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality. When AQI values are above 100, air quality is considered to be unhealthy, at first for sensitive (to the harmful components) groups of people, then for everyone as AQI values get higher.

The AQI categories are:

0 to 50 Green Good
51 to 100 Yellow Moderate
101 to 150 Orange Unhealthy for Sensitive Groups
151 to 200 Red Unhealthy
201 to 300 Purple Very Unhealthy
301 to 500 Maroon Hazardous

Each category corresponds to a different level of health concern. The six levels of health concern are:

"Good" - The AQI value is between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.

"Moderate" - The AQI value is between 51 and 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a small number of people.

"Unhealthy for Sensitive Groups" - The AQI value is between 101 and 150. Members of sensitive groups may experience health effects. The general public is not likely to be affected when the AQI is in this range.

"Unhealthy" - The AQI value is between 151 and 200. Everyone may begin to experience health effects. Members of sensitive groups may experience more serious health effects.

"Very Unhealthy" - The AQI value is between 201 and 300. This triggers a health alert, because everyone may experience more serious health effects.

"Hazardous" - The AQI value is over 300. This triggers health warnings of an emergency nature. The entire population is more likely to be affected.

People living in close proximity to the fire-stricken areas should remain indoors and avoid inhalation of smoke, ashes, and particulate matter in the area. Ordinary dust masks, designed to filter out large particles, will not help as they still allow the more dangerous smaller particles to pass through. HEPA filter masks can remove nearly all airborne particles 0.3 micrometers (microns) in diameter, but they are more expensive and may be difficult to use for people with lung disease, because it can be hard to draw air through them.

If outdoor trips in smoky areas are necessary, breathing through a damp cloth may help filter out some of the particles that are floating in the air, but this is a temporizing measure only and should not be counted upon to significantly diminish smoke exposure for more than a few minutes.

Preview the 25th Anniversary & Annual Meeting of the Wilderness Medical Society, which will be held in Snowmass, Colorado July 25-30, 2008.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.