Coping with the health effects of wildfire smoke requires both community cooperation and some individual judgment and ingenuity, experts say.
How much smoke we're exposed to depends on a number of things, from the direction the wind blows to the type of fuel feeding a fire to the terrain around the blaze.
Smoke typically dilutes with distance, but plumes carried hundreds of miles can still contain particles sufficient to affect health.
The Environmental Protection Agency, the federal Centers for Disease Control and Prevention and most state health departments offer guidance about coping with wildfire smoke.
The following tips were gleaned from a guide for public health officials on wildfire smoke, written by a team led by Dr. Michael Lipsett, chief of the environmental investigations branch of the California Department of Health, and presentations by Michael Brauer, associate professor of environmental hygiene at the University of British Columbia, along with interviews with a number of other experts.
* What levels of smoke are dangerous?
If you live in an area where air quality measurements are taken, those readings can provide some warning. Levels of fine particulate matter higher than 89 units per cubic meter of air over a one- to three-hour average are unhealthy for sensitive groups such as people with asthma, lung or heart disease; 139 or higher are unhealthy for everyone.
But keep in mind that monitors may report readings only once or twice a day. Fire and smoke conditions can change in minutes, and public health officials may not be able to issue timely warnings.
Another way to measure smoke is visibility -- if it is limited to 3 to 5 miles in dry conditions, levels are unhealthy for sensitive people. Less than 2 3/4 miles is unhealthy for everyone.
The most important clue is how your body reacts. If you can smell smoke, you're probably being affected.
Experiencing irritated eyes, throat or lungs, as well as breathing difficulty, chest discomfort or a persistent cough when smoke is present, are all warnings to take protective measures or seek medical care, particularly if you have a history of breathing problems or heart disease.
* How do we avoid the smoke?
Leave the area. People who are sensitive to smoke may need to evacuate.
Consider going to a clean-air shelter set up by local health authorities if one is available. Some evacuation centers have separate interior rooms away from doors or windows to serve people with breathing problems. Temporary relief can be found in places like malls, theaters and public buildings with good air- conditioning systems.
Shelter at home. If your home is tightly built and air-conditioned, even sensitive people should be able to avoid the worst effects.
A high-efficiency filter on a whole-house air system is a good investment. Homes without whole-house AC may still be safe if you can seal up a room, keep it air-conditioned and use a good HEPA air filter.
If you're going to shelter at home, make sure you have medicine and supplies to stay indoors at least five days. Limit exertion in the home and trips outside to short jaunts in an air-conditioned car, with vents closed, and the AC in "recirculate" mode if possible.
* What can healthy people do outdoors when wildfire smoke is present?
Outdoor exercise should be limited whenever air is at unhealthy levels; schools should cancel sporting events and other activities. People who must work outdoors -- public-safety workers, mostly -- should wear masks and take frequent breaks.
Workplaces, such as garages, factories and warehouses, where it's impossible to seal out smoke, should limit operations and take steps to protect workers when smoke levels are high.
Pets and domestic animals are also sensitive and need to be protected.
* What sort of respiratory masks can help protect people from smoke?
Disposable particulate respirators rated N95 or P100 by the U.S. National Institute for Occupational Safety and Health offer good protection from small particles in smoke, but not against other toxic fumes.
The masks, sold in many hardware stores, must fit tightly, using two sets of straps above and below the ears, and be replaced regularly.
Other types of industrial respirators, such as those used by painters, fitted with particulate-filtering cartridges, may also be helpful.
Paper "dust" masks or surgical masks offer no protection from smoke. People with heart or lung conditions should not use the respirators because they can restrict breathing.