Working Knowledge: Breathing Easier?; January 2002; Scientific American Magazine; by Mark Fischetti; 2 Page(s)

The spread of anthrax in the U.S. that began in October has spurred many people to buy gas masks. But the gear's effectiveness may be misunderstood. A mask's filter canister is intended to stop particles such as anthrax, chemicals such as nerve gas, and germs such as smallpox. The respirators come as face masks that protect the mouth, nose and eyes and as hoods that envelop the head.

U.S. certification is done by the National Institute for Occupational Safety and Health (NIOSH) and the armed services. Two key parameters are the size of the smallest particle the filter traps (the best are 0.3 micron) and the efficiency of gases the filter removes, rated at 95, 99 or 99.97 percent.