Should citizens buy gas masks?

No. The most current advice provided by the Centers for Disease Control is that gas masks are not recommended for the general public. They need to be fitted carefully for each face, and there are different kinds of masks for different types of agents. Having or using a gas mask may offer a false sense of security. They can also be unsafe for children or people with asthma.

The chances that terrorists will turn to poisonous substances instead of conventional bombs are very, very remote. Various news reports have noted that citizens are opting to purchase protective masks as a way to defend against chemical or biological terrorism. There are several important factors to bear in mind when considering this option.

In order for a mask to protect you against a chemical weapons attack, you would need to carry the mask with you at all times---24 hours a day, 7 days a week---and be prepared to put it on immediately if chemical emergency was suspected. To guard against a biological attack, you would need not only to carry the mask but also wear it at all times, since the presence of biological agents is not obvious without advanced sensors.

Gas masks capable of effectively protecting people from either chemical or biological agents are not a "one size fits all" purchase. At this point there are many different sizes and brands of masks available on the open market. It is critically important to make sure that the mask fits you properly---a loose gas mask defeats the purpose. Reputable dealers would be able to provide instructions not only on finding the right mask fit, but also on how to put it on, how to maintain it, and how to take care of the filters the mask uses as a barrier against microscopic particles.