Which is why, as CBS News Correspondent Wyatt Andrews reports, it has stunned some rescue teams to learn that almost none of the masks used today can seal out poison gas.
In a government test developed after Sept. 11, either mustard or sarin gas penetrated every major mask, except one used in only a handful of cities.
In the age of "orange" terrorism alerts, the failure of the masks is shocking news.
When he received the report, the chief of the Arlington Virginia Fire Department, Ed Plaugher, says he was, "devastated - literally devastated."
Plaugher led the Sept. 11 response at the Pentagon. Even though his rescue teams presumed there might be poison gas, they rushed in anyway, certain their gear would protect them. That confidence is gone.
"The failure of the test is a very, very big deal for us, because it means we have to re-evaluate and re-ramp the way that we attack an incident like this," says Plaugher.
What he means is delay. Today, if the alarm rings and a gas attack is suspected, the Arlington teams will not rush in.
"This is going to cost lives," he says. "This is going to delay rescues, absolutely."
Fire departments all over America, especially in places where terrorists might attack, face a tough choice. They can subject their rescue teams to a higher level of risk, which is dangerous, or replace or retrofit their masks, which is expensive.
According to Harold Shaitburger, the chief of the International Association of Firefighters, it would cost hundreds of millions of dollars.
Shaitburger says the federal government must step in because local governments can't afford new equipment.
"This goes to the heart of what is homeland security all about," he says. "It's a national responsibility, it is a federal effort."
It could be years before masks that can handle poison gas reach the teams that need them. But today rescue teams on high alert for the next attack could face the unheard of order to hold back.