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Fire Entrapments



Previous Studies of Vehicle Burnovers


Test Procedures and Methods

Test Results



About the Author

Appendix A - Vehicle Entrapment Study Plan

Appendix B - Characterizing Gases Generated in Vehicles and Fire Shelters

Appendix C - Insulated Boxes for Protecting Video Cameras

Also read about engine entrapment incidents:


Fire Entrapments
Comparing Conditions Inside
Vehicles and Fire Shelters

Test Procedures and Methods

Because the study's objective was to quantify conditions in an engine compared to a fire shelter, test procedures and methods had to realistically measure the critical factors in a fire entrapment.

A study plan developed by the staff at MTDC was given wide review by cooperators, Forest Service fire specialists and researchers, and other fire specialists in the United States, Canada, and Australia. The final version of the study plan is in Appendix A.

Vehicles were positioned in or adjacent to fuels as they would normally be configured in a typical wildland setting:

  • In the grass fuel type, they were placed in the middle of the fuels, with no clearing.
  • In the brush and timber fuel types, engines were placed on roads, immediately adjacent to the fuels, but not in direct contact with them (Figure 7).

Figure 7-Both vehicles and fire shelters were placed right beside fuels. Firefighters would normally set up their shelters farther from the fuels, but the test compared fire shelters and vehicles under the worst conditions.

Fire shelters, both the Forest Service's standard model and a stainless steel prototype, were erected in front of or behind an engine, using tent framing to keep them erect. Weights along the inside edge of the shelter simulated a firefighter holding the edges to keep them from rising during the burnover. These shelters were adjacent to the fuels, rather than in a preferable deployment site as far from the oncoming fire as possible. This ensured that the data gathered were fully comparable to that obtained from the engines.

Instrumentation on the sites included two poles 9 feet (3 m) tall outfitted with thermocouples every 6 inches (15 cm). Data were recorded on Campbell Scientific data loggers, providing vertical temperature profiles on the burnover site. Radiometers were placed at the front or rear bumpers of the engines and on poles (Figure 8) to measure radiant heat flux. In the passenger side of the cab, 4-foot (1-m) thermocouple "trees" were outfitted with thermocouples every 6 inches (15 cm). The data were recorded on Campbell Scientific data loggers.

Figure 8-Radiometers on these poles measured radiant heat flux.

The fire shelters had thermocouples attached at the foot end, on the shelter's inside and outside skin. Thermocouples were placed at the head end of the shelter, 1 inch (3 cm) and 12 inches (30 cm) above the ground to measure air temperatures in an entrapped firefighter's critical breathing zone.

Both the engines and fire shelters had gas collection devices (Figures 9 and 10) placed inside to measure gases that could be harmful or fatal to an entrapped firefighter. The breakdown of materials inside the engine cab, such as the volatilization of petroleum-based plastics and sound-deadening materials inside the door panels, were a special concern, as was the off-gassing of the fire shelter adhesive that bonds the aluminum foil to the glass cloth. Detailed documentation of the gas collection system used on these burns-and on the gases collected-can be found in Appendix B.

Figures 9 and 10-Gas collection devices sampled gases inside vehicle cabs. Instrumentation was buried inside ammunition boxes so that it would survive the fire.

Personal protective clothing (Figure 11), equipment, and other items commonly used by wildland firefighters were laid out near the fire shelters to visually evaluate their protective value during an entrapment. Items included the standard Forest Service Nomex shirt and trousers; leather firefighter gloves; hardhat; military-issue flight suit; and various outer garments such as brush coats, FR coveralls from Canada and Australia, and shirts from various cooperators.

Figure 11-Personal protective clothing was laid out to observe the fire's effects on it.

Clothing was tested as though it were on a firefighter. Five-gallon water bladders were filled with water and covered with 100% cotton undershirts. The shirts and jackets (or flightsuits) were placed over the undershirt. The bladder filled out the garments and simulated a heat sink, not unlike that of the human body. While some of these items were not instrumented, we felt visual observation of damage would offer valuable lessons for firefighter training. Specialized fireproof video photography equipment (Figure 12) was developed to take closeup shots of the fire's effects on the engines and shelters. These boxes were designed to withstand temperatures as high as 2300 °F (1260 °C) for extended periods (see Appendix C).

Figure 12-Video cameras were set up inside specially designed fireproof boxes to observe the fire from several vantage points.

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