JOHN K. WILEY
Associated Press Writer

SPOKANE, Wash. (AP) -- An aluminum and fiberglass tent designed to shield firefighters from flames is credited with saving more than 250 lives _ but not those of four firefighters killed in a wildfire this week.

The emergency foil shelters, which take about 45 seconds to deploy, have been standard issue for the U.S. Forest Service since 1970. But a redesign was under way even before the fatal blaze, based on tests showing that direct flames can break down the materials.

The firefighters who died deployed their pup tent-like shelters Tuesday when the small wildfire they were battling exploded in size and sent walls of flame after them.

Fire officials say the silvery shelters are a last resort when all other efforts to escape have failed. Firefighters call them ``shake and bakes.''

``All firefighters would say they don't want ever to be in a position to deploy a fire shelter,'' said Don Smurthwaite, a spokesman with the National Interagency Fire Center at Boise, Idaho. ``It is the last line of defense. It is the last option.''

Investigators from the Forest Service Technology and Development Center at Missoula, Mont., were sent to the Cascade Range site where the four Forest Service firefighters died. The investigators will probably use data from those deaths to improve the shelters, Smurthwaite said.

When an approaching wildfire threatens to overtake them, firefighters drop their gear and pull plastic release handles to free the compressed shelters from a vinyl bag.

Ideally, the firefighter would have cleared a 4-by-8-foot space of grass and debris. Then, the firefighter steps into leg and hand straps and lies face down on the ground, pulling ground flaps along the bottom to seal out heat and gases.

The shelters, designed to reflect 95 percent of a fire's radiant heat, trap breathable oxygen while the fire makes its run. They can also be used as a body covering to protect a firefighter who decides to run through flames.

During the fatal blaze on Tuesday, a firefighter rescued a couple by cramming them into her shelter, which is designed for one person but can hold two in a pinch. The firefighter, Rebecca Welch, 22, suffered burns on her right side because she could not get completely inside the survival tent along with the couple. The couple, who had gone into the area to hike, were treated for smoke inhalation and burns.

Tim Eldridge, a spokesman with the federal Aerial Fire Depot in Missoula, Mont., said the shelters do not do well in direct flame, which causes the glue used to laminate the fiberglass and foil to deteriorate and burn.