by Joshua Fody and Tony Petrilli
In 1959, the U.S. Forest Service, Missoula (Mont.) Equipment and Development Center began development work to design an emergency fire shelter for wildland firefighters. The first documented use of a fire crew using fire shelters for protection from a fire was in 1964 in Southern California, thirty-six lives were saved by the experimental fire shelters.
In 1967 fire shelters were mass produced for firefighters to carry when it was deemed necessary. The early version of the fire shelter was aluminum foil laminated to fiberglass fabric with a Kraft paper liner designed into an A-frame structure.
During the 1970s, the paper liner was eliminated in the design. Policy was changed in 1977 to require all US federal firefighters to carry fire shelters while working fires. Minor changes were made to the design during the 1980s and 1990s. From 1964 into the 2000s, it is estimated the fire shelter saved 300 lives, and prevented serious burn injury to another 300 firefighters; however, 20 firefighters died in fire shelters during that sametime period.
In 2000, Forest Service Fire Management officials directed the now named Missoula Technology and Development Center (MTDC) to pursue development of a more protective fire shelter. Many new materials and shelter designs were considered and tested. Interagency Fire Directors selected the New Generation Fire Shelter in 2002. This new shelter shows marked improvement in protection vs. the old-style shelter, but it is not able to provide sufficient protection in the most extreme fire conditions.The shelter is constructed into a rounded shape and is made of two layers of laminated material. The outer layer is made of woven silica laminated to aluminum foil, while the inner layer is made of woven fiberglass material laminated to aluminum foil.
There have been 159 new shelters deployed, saving 25 lives and preventing 102 firefighter burn injuries; however, 21 lives have also been lost. Nineteen of those lives were of the Granite Mountain Hotshot Crew in an incident near Yarnell, AZ on June 30, 2013.
The Fire Shelter Project Review was initiated in 2014. The project is pursuing advances in materials that may offer increased protection by slowing the transfer of heat through the shelter layers. Historically, many high-temperature resistive materials are relatively heavy, bulky, fragile and/or toxic. These are all attributes that are not suitable for fire shelters. A few entities are submitting promising materials for testing, one of those is the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) located in Hampton, Virginia.
For the past decade, NASA LaRC has been conducting materials development of flexible high temperature insulations for use on inflatable heat shields. Projects such as the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) are designing these novel inflatables for the delivery of large payloads to Mars. The use of a large heat shield made of conventional rigid materials, like the one used on the Apollo capsule, is impractical for this type of application. By creating an inflatable structure, heat shields 20 feet in diameter, or larger, can be packed down to less than 20% of their original diameter, allowing them to fit into launch vehicles of a practical size.
Highly efficient, flexible, durable, thin, and lightweight insulations are required to protect these inflatable structures from the enormous heat of re-entry, and there are several similarities between NASA’s flexible heat shields and the fire shelter. After learning of the tragedy at Yarnell Hill, NASA LaRC researchers reached out to MTDC to offer their expertise and assistance in the development of new materials and shelter designs for the Fire Shelter Project Review, with the goal of providing a safer shelter for future fire fighters.
The NASA fire shelter development effort became known as Convective Heating Improvement for Emergency Fire Shelters (CHIEFS), and was tasked with improving the fire shelter’s resistance to direct flame exposure. The CHIEFS team quickly realized that flexible heat shield materials used for atmospheric re-entry vehicles could not be directly applied to the fire shelter. Flexible heat shields are designed to withstand more than 10 times the thermal load of a typical forest fire and consequently materials are too robust to be appropriate for the tight mass and volume constraints of the fire shelter. However, the experience amassed during the development of flexible heat shields has proven advantageous to CHIEFS research.
CHIEFS began work by developing a small scale convective heating test apparatus based on existing test standards used by the U.S. Forest Service, which employs a propane flame to rapidly screen various material samples. To date, CHIEFS has used this small-scale apparatus to test the thermal performance of more than 300 unique material layups – combinations of multiple individual layers – and in doing so has evaluated more than 70 individual materials.
The individual material layers in a layup can be selected to target the suppression of various modes of heat transfer; the order of these layers is also important. By parametrically varying the composition and ordering of these layups, candidate fire shelter concepts can be optimized to provide maximum thermal protection while maintaining acceptable levels of mass, volume, durability, toxicity, and cost.
Once past the initial screening, promising candidate materials are manufactured into full-scale fire shelters for further testing. During the summer of 2015, the first round of CHIEFS full-scale shelters – along with shelters submitted to MTDC by other vendors – were evaluated in both controlled wildfires in Canada as well as in a series of controlled laboratory fire enclosure tests. All CHIEFS shelters performed well thermally, and the tests also provided many “real world” lessons, not realized in the earlier small-scale development, that are now being implemented into a second round of CHIEFS shelters.
Currently, CHIEFS is completing fabrication of their next round of full-scale fire shelters. These shelters will undergo preliminary evaluations, and then promising candidate layups will be evaluated in another round of full-scale shelter testing. This testing will take place along with candidates from other vendors in spring, 2016, at the MTDC. The goal is to have shelters with a significant increase in performance with minimal increase in weight and bulk that then can go forward to field testing. The CHIEFS team has thoroughly enjoyed their collaborative effort with MTDC, and is excited to continue development of more efficient fire shelters and help make our nation’s wildland firefighters safer on the ground.
Josh Fody was born and raised in Colorado. After serving as an enlisted sailor in the US Navy for 4 years working on the flight deck and in the jet shop performing intermediate level maintenance on aircraft power-plants, he attended CU Boulder for his undergraduate degree and later completed a Master’s Degree in Mechanical Engineering at the University of Maryland. His research primarily focused on enhanced evaporator concepts for alternate energy generation. After defending his thesis, he took a job at NASA Langley where he has been working in the Structural and Thermal Systems Branch for the past 2 years as a thermal analyst.
Tony Petrilli is an Equipment Specialist with the US Forest Service at the Montana Technology and Development Center (MTDC).