Health officials do not recommend the use of gas masks, which are not designed to provide protection against biologic agents.  Gas masks would only protect against chemical agents if worn at the time of release.  Since gas masks are only effective for several hours without changing cartridges, it is impractical for persons to be wearing these masks continuously.  As they nee to be fitted properly, improper use of gas masks can cause serious injury or even death, especially among persons with underlying heart or lung disease.