Beginning this summer, firefighters will carry a new wildland fire shelter developed by the Missoula Technology and Development Center (MTDC). The new generation shelter will provide improved protection from radiant heat and flames.
Wildland firefighters have carried fire shelters since they were developed during the 1960s. More than 1,100 firefighters have deployed their fire shelters. The shelter is credited with saving more than 300 lives and preventing hundreds of burn injuries. Although the original shelter (which this Tech Tip will call the standard fire shelter) was designed to reflect radiant heat, direct flame contact can cause damage. Fatalities have occurred when flame contact was severe.
In January 2000, MTDC was asked to develop an improved fire shelter. The goals of the project were to maintain the protection from radiant heat provided by the standard shelter while improving protection from direct flame. Other considerations included material strength, durability, flammability, weight, bulk, toxicity, and cost.Development Process
The first step in the development process was to devise tests to evaluate the performance of the prototype shelter materials and designs. Small-scale laboratory tests were designed to allow screening for strength, flammability, thermal performance, and toxicity. Full-scale tests were developed to measure the strength, durability, flammability, thermal performance, and toxicity of the overall shelter designs. Over 60 materials and combinations of materials were considered. Seventeen full-scale designs were tested. The Federal Fire and Aviation Leadership Council selected the final shelter design in June 2002.The New Design
The shape of the new generation shelter differs from that of the standard fire shelter (figure 1). The shelter is now shaped like a half cylinder with rounded ends. The new shape has a number of advantages. The rounded design reduces the surface-area-to-volume ratio, decreasing the amount of material needed to provide enough volume inside the shelter. The new materials improve protection from flames, but they weigh twice as much as the old materials. If the new materials had not been used efficiently, the new shelter could have weighed more than twice as much as the standard shelter.
The new shelter is narrower and longer than the standard shelter. Overall, the shelter offers significantly more protection than the standard shelter, but it will feel smaller to users.
The new design's reduced surface-area-to-volume ratio improves protection because the shelter has less surface area to absorb radiant heat. The rounded ends also solve a problem noted during field testing of the standard fire shelter. Video footage taken during test fires showed that the flat ends of the standard shelter could reflect heat onto adjacent fuels, igniting them before the flame front arrived. Flames from adjacent fuels could damage the shelter, reducing its protection when the flame front arrived. The rounded ends of the new shelter scatter radiant heat to the atmosphere, rather than focusing heat on fuels next to the shelter.
The new shelter is made of two layers of material (figure 2). It weighs 4.2 pounds, compared to about 3.4 pounds for the standard shelter. The outer layer is woven silica laminated to aluminum foil. The inner layer is fiberglass laminated to aluminum foil. The outer layer of foil reflects radiant heat and the woven silica slows heat transfer to the inside of the shelter. The inner layer of foil prevents heat from being reradiated inside the shelter, and it prevents gases from entering the shelter. When the two layers of material are sewn together, the air gap between them provides additional insulation.
Seams across the top of the shelter support the shelter's main shell. The seams also help keep the outer foil layer in place. When the shelter is heated to 260 °C (500 °F), the adhesive that bonds the foil to the silica breaks down, allowing the layers to separate. In turbulent conditions, the foil can tear and peel away from the silica layer. Seams protect the foil layer because foil stops peeling when it reaches a seam.
The new shelter's carrying case is blue. The pull strap for removing the shelter from the case is yellow. The new shelter, like its predecessor, should always be carried inside its hard plastic liner. The new generation shelter will be available through the General Services Administration (GSA) Wildfire Protection Equipment and Supplies catalog by June 2003. See the ordering information at the end of this document.