USDA Forest Service
Technology and Development Program
As engines are more widely used, the risk that fire will burn over the engine increases. Protective clothing and equipment (such as the fire shelter) are well accepted in the fire community. A wide range of opinion has been expressed concerning the protection an engine might afford during a burnover.
In recent years firefighters have been entrapped in their engines during a number of incidents. They have been forced to make instantaneous decisions about their best chances for survival: in an engine, or in a fire shelter.
Figure 1-This engine burned during the 1995 fires on Long Island. Although many engines were destroyed, all firefighters escaped without injuries.
Figure 2-The cab interior of the same engine burned during the 1995 fires on Long Island.
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Figure 3-Layout for the June 5 burn in Los Angeles County.
The specific factors to be measured included:
Figure 4-Several types of fire shelters were tested, including the standard Forest Service fire shelter and prototypes from MTDC and a private firm.
There is no intention on the part of MTDC or the WO Fire and Aviation Management in this study to set policy to determine whether firefighters should remain in a vehicle or deploy a fire shelter- rather, the study should provide as much quantifiable data and observations as possible so managers can formulate policies that apply specifically to their agencies.
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Figure 5-This engine burned during the 1990 Toolara Fire in Australia. Three firefighters were trapped, one of whom was badly burned when he ran for safety. The other two men stayed in the vehicle, spraying themselves with water until the tires caught fire. Then they too ran for safety.
In a 1972 report, Studies in Human Survival in Bushfires, Cheney reported that temperatures within a few feet of the ground and within a few feet of trees up to 35 feet (11 m) tall were lower than 120 °F (49 °C). In vehicle tests, car windows blocked half the radiant heat, but occupants would have still received severe burns to their bare skin. Within 4 minutes after the test fire was ignited, temperatures inside the vehicle reached 390 °F (199 °C). The roof lining and rubber seals burned, filling the cab with thick, dense smoke. Plastic and rubber material used in the interior lining smoked, causing "severe discomfort; tyres were caught alight by severe radiation heating; and 8 to 10 minutes after peak radiation, the engine compartment caught alight and burned strongly."
In a 1995 personal communication, Cheney recounted his experience on a bush fire during 1965 when the Australian version of the fire shelter was being developed. He believes he took additional risks because he had a fire shelter, that it was very hot and uncomfortable inside the shelter, and that he would have been safer if he had stayed in his vehicle.
In an April 1996 article, New Fire Tactics for New Car Fires, Bill Gustin discusses the hydrocarbon-based synthetic materials now used to reduce vehicle weight. He says that these materials produce thick, toxic smoke, "a witches brew of toxic gases." He also discusses the possibility of explosions from tires, batteries, hollow drive shafts, and components of the air-conditioning system. The plastic fuel lines used in newer vehicles carry gasoline at 15 to 90 psi. An electric fuel pump pumps gasoline from the tank to the engine. If a fire causes the fuel line to leak, gasoline will be under pressure, resulting in a sudden, intense fire fed by a spray of atomized gasoline.
Fuel tanks can no longer be vented to the atmosphere because of environmental concerns. Instead, vapors are pumped into a charcoal canister in the engine compartment. Excessive pressure from the heat of a fire could cause the fuel tank to leak along a seam, spilling fuel to the ground, increasing a fire's intensity. Fuel tanks made of polypropylene are lighter than metal tanks, but would melt more quickly.
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The availability of engines that could be destroyed when subjecting them to the full effects of direct flame was critically important. In response to requests over the Internet, personal contacts, and interagency contacts throughout the wildland fire community, surplus engines were identified at the Florida Division of Forestry, Los Angeles County Fire Department, and the Montana Department of Natural Resources and Conservation. These engines enabled MTDC to fully implement the test plan as designed, with the engines and fire shelters exposed to a flaming front of fire for varying durations in a variety of fuel types.
Once engines were available, suitable sites had to be found where prescribed burns could be ignited under conditions similar to an engine burnover without damaging the site. Several of the agencies that contributed engines to this study also offered areas where burns could be conducted that met all of the criteria: where engines could be easily accessed and observed, where fire could impact both engines and shelters simultaneously, and where the risk of fire escape was minimal. The Florida Division of Forestry (Figure 6) and the Los Angeles County Fire Department offered burn sites that met these criteria. Both agencies had surplus engines available nearby. In Florida, lands of the Lake Butler Forest Unit of the Georgia-Pacific Corporation were selected. In Montana, the Beaverhead National Forest offered a site where we could to test the engines from the Montana Department of Natural Resources and Conservation.
Figure 6-Cooperators provided vehicles used in the tests, such as this engine and pickup provided by the Florida Division of Forestry.
Because the purpose of this study was to quantify the effects of flame and heat on the engines and fire shelters, scientific procedures had to be used when measuring:
Dr. Bret Butler of the Forest Service's Intermountain Fire Sciences Laboratory in Missoula provided valuable expertise gathering and processing much of the data discussed throughout this report.
Preparing all the equipment, vehicles, and instrumentation for the test burns was labor intensive. Several smokejumpers from the Forest Service's Aerial Fire Depot in Missoula, MT (detailed to MTDC), helped complete these tests. In addition, the MTDC employees who helped implement the test plan were: Jim Kautz (photography), Lynn Weger (gas chemistry), Loren DeLand and Dave Gasvoda (instrumentation), and Ted Putnam and Bob Hensler (fire shelters and PPE).
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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:
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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The first burn was conducted on February 27, 1996, on an open, grasscovered field that had dry, cured bunchgrasses 30 to 36 inches (76 to 91 cm) tall, with a 2- to 4-inch (5 to 10 cm) mat of cured grass and thatch on the ground. The burn was in late afternoon with a 3- to 5-mile per hour wind. It was over in less than 1 minute, and had neither the intensity nor the duration to seriously test the survivability of the shelters or the engines (Figure 13).
Figure 13-The Florida burn was not intense enough and did not burn for long enough to seriously test survivability inside either the shelters or the vehicles.
Despite the brief duration and low intensity of this burn, some meaningful data were gathered:
Figure 14-The change in color of the pants shows the effect of heat. Water bags inside the fire shirt and upper pants served as a heat sink, keeping them from becoming as hot as the pant legs.
A second burn was planned in a heavier palmetto-galberry fuel type (NFFL Model 7). Heavy rains prevented us from conducting the burn as planned.
In summary, this burn served as a good "shakedown" for the procedures and techniques used in future tests, but it was not long enough or hot enough to develop meaningful data about the differences between the protection offered by a fire shelter and an engine cab.
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Two burns took place on June 5 and 6, 1996, in dry, cured grasses 12 to 24 inches (30 to 61 cm) tall, with a 2- to 3- foot (0.6- to 0.9-m) chamise brush overstory (NFFL Model 5). Air temperatures were approximately 32 °C, with wind speeds of 5 to 10 miles per hour (8 to 16 km per hour) during the burns. Flame lengths averaged 12 to 20 feet (4 to 6 m), with short periods (less than 30 seconds) where lengths were 20 to 30 feet (6 to 9 m).
The June 5th burn took place on slopes averaging 70%. The engines, fire shelters, and PPE were on a road near the top of the slope (Figure 3). Flames came in direct contact with the engines and shelters, since they were positioned at the road's edge to receive the maximum effect of the flaming front (Figure 15).
Figure 15-This image (taken from video) shows the intensity of the June 5 burn in Los Angeles County.
This burn occurred in heavier fuels and on a day with higher air temperatures than the Florida burn. It produced a significant amount of meaningful data:
Figure 16-These items of personal protective clothing show the effects of the June 5 burn in Los Angeles County. Note the difference made by being just a few feet from the edge of the roadway.
Figure 17-Mudflaps are just one of the flammable items on the engine's exterior.
|Gases (parts per million)||Engine||Shelter|
The second burn in Los Angeles County was on June 6th, the next day. Weather conditions were nearly identical, but the slope, aspect, and fuel loading were different. The engines were positioned at the head of a small draw with 35 to 45% slopes (Figure 18). Some chamise brush was cut and piled next to the engines and shelters to increase the fire's intensity and duration. Because of the topographic effect of some adjacent spur ridges, the flames were diverted from the engines and shelters.
Figure 18-The engine, patrol engine, and fire shelters positioned for the second burn in Los Angeles County, June 6th.
Although the engines and shelters had less direct flame contact than expected, important data were obtained from the effects of the radiant heat load:
Figure 19-The patrol engine caught fire during the June 6 burn in Los Angeles County.
Figures 20 and 21-Firefighters put out the fire in the cab of the patrol pickup. Material on the inside door panel burned, emitting smoke that would have forced entrapped firefighters to leave the truck.
LOS ANGELES-JUNE 5TH
LOS ANGELES-JUNE 6TH
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The test burn was conducted in late July in an area of thinned lodgepole pine slash that had been piled about 5 feet (2 m) high, 8 feet (2 m) wide, and 200 feet (61 m) long. Air temperatures that day were in the mid-70's (about 21 °C), with humidities in the low 20's. The engines, fire shelters, and PPE were laid out beside the edge of the slash piles to obtain maximum heat load.
An unforecast wind shift just before ignition prevented direct flame contact on the vehicles and shelters being tested (Figure 22).
Figure 22-Wind prevented flames from directly contacting vehicles during the test burn near Dillon, MT.
However, satisfactory results were obtained:
Figure 23-Even though flames did not directly contact the 212-ton truck, its cab caught fire.
Figure 24-This hardhat shows the difference a few inches can make at ground level. The hardhat melted where it was closest to the fire, but wasn't damaged just a few inches away from the heat.
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Figure 25-Even after a fire has passed, a vehicle retains heat, acting as a "heat sink."
Figure 26-When a fire comes up a steep sideslope, it appears to go over and under the engine, creating an eddy on the back side that draws heat and flame.
Figure 27-Items on an engine's exterior may catch fire during moderate-intensity, short-duration fires.
Figure 28-Items on an engine's exterior may catch fire during moderate-intensity, short-duration fires.
Figure 29-Even though the engine is on fire, the shelters and personal protective clothing are undamaged.
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Bond, A.; Cheney, N. P. 1986. A discussion paper on techniques and equipment for bush fire fighters entrapped by fire. Canberra, Australia: CSIRO National Bush Fire Research Unit.
Cheney, N.P. 1972. Forestry and timber bureau studies human behavior in bushfires...don't panic and live. Canberra, Australia: CSIRO Division of Forestry. NAT/DEV: September 1972.
Cullom, Keith D. 1986. The breaking point: twice in one season. Boston MA: National Fire Protection Association. Fire Command. March 1986: 22-27.
Douglas, D. R. 1969. Safety as a factor in the design of fire-fighting vehicles. In: South Australian Emergency Fire Services E.F.S. Manual: 30, 32, 34, 47.
Gustin, Bill 1996. New fire tactics for new-car fires. Fire Engineering. April 1996: 43-54.
Harris, J. P. 1997. Calabasas Incident entrapment analysis. Los Angeles, CA: County of Los Angeles Fire Dept.
Knight, Ian 1988. What intensity of fire can a fire fighter survive in a reflective shelter? Boston, MA: Fire Technology. November 1988: 312-331.
Mangan, Dick. 1993. New standards for wildland firefighting protective clothing and equipment. Tech Tip 9351-2340-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and Development Center.
Mangan, Dick. 1995. Safety zones versus survival zones (Recommendations B.5 and B.8). In: Interagency Management Review Team on South Canyon Fire: Final Report.
Mangan, Dick. 1994. Lessons learned: the use of personal protective equipment on wildfire entrapments in 1993. Tech Tip 9451-2335-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and Development Center.
Mangan, Richard J. 1996. Wildfire safety: equipment, training and attitudes. In: Seminar on Forests, Fire and Global Change. Sushenskoye, Russian Federation.
McArthur, A. G.; Douglas D. R.; Mitchell, L. R. 1966. The Wandilo Fire, 5 April 1958: fire behavior and associated meteorological and fuel conditions. Leaflet No. 98,O.D.C. 431.6. Canberra, Australia: Department of National Development, Forestry and Timber Bureau, Forest Research Institute.
National Fire Protection Association Committee on Fire Gas Research. 1952. Fire gas research report: report of research by Arthur D. Little, Inc. Quarterly. January 1952. Boston MA: National Fire Protection Association.
Putnam, Ted 1995. Your fire shelter: 1995 edition. Tech. Rep. 9551-2819- MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and Development Center.
Putnam, Ted 1996. Your fire shelter- beyond the basics: 1996 edition. Tech. Rep. 9651-2829-MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and Development Center.
Queensland Forest Service. 1992. Swampy Fire no. 7-S.F. 1004: Toolara State Forest -22 September 1991. Queensland, Australia: Queensland Forest Service.
Smith, J. E. 1994. Fire storm: after action report. Arroyo Grande, CA.
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Firefighter PPE will also be placed around filled 5-gallon water bags and laid in the same area as the shelters to assess visual indicators of heat load and fire effects.
Florida: February 23 to March 1, 1996
California: mid-April to mid-May, 1996.
Phone: (906) 488-6111
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On February 26, 1996, this equipment was deployed on a cured bunchgrass/ matted grass-thatch site at Lake City, FL, a day before the prescribed burn planned for the vehicle entrapment study. A FASS package was set up to monitor the air in each of the two vehicle cabs. The third FASS monitored the air inside a standard aluminum fire shelter.
The FASS had to be modified to fit in the vehicles and the shelter. The particulate- collecting "heads" were positioned where a human would be breathing inside the cab or shelter. After particulate is collected on filters in the head, pumps that deliver a flow of 2 liters per minute draw gases through inert Teflon tubing to collection canisters and real-time sensors. The real-time data are recorded on data loggers. The tubing is protected by a loose, flexible ceramic sheathing. The tubing umbilical exposed in the cab was threaded through an aluminum pipe to support the head and umbilical and to provide protection from the high temperatures. The aluminum pipe extended from the cab interior, through the cab floor, to the ground. The 50-foot umbilical (with Teflon tubes inside) was stretched from the lee side of the shelter or vehicles to the main body of the FASS package that holds the sensors, pumps, data loggers, and canisters. The lee side refers to the side of the shelters and vehicles opposite the fire's expected approach. The umbilical and FASS were buried after they had been assembled, calibrated, and armed. The aluminum pipe inside the shelter was slanted from the FASS head to the ground, roughly simulating the position of a human body lying in a shelter. After the arm plug has been pulled, these FASS packages activate once they sense a predetermined level of carbon monoxide. Carbon monoxide is a product of incomplete combustion that will always be produced in a fire. It is one of the first gases produced and its concentration spikes sharply early in any fire episode. The passive Drager tubes were hung inside the cabs and shelter where they were protected with high-temperature foil and tape. The tubes, like the FASS heads, were positioned in the approximate area where a human would be breathing.
A short-duration, low-intensity burn took place the next day. The results were disappointing. One package failed to trigger, while data from the other packages were negligible. The Drager tubes showed no color change. A second burn attempted a few days later in a Palmetto site was cool and spotty because of precipitation. Results were negligible and the Drager tubes indicated no color change.
This burn yielded two major conclusions. Future burns needed to be of high intensity and long duration. In addition, we learned that we needed to develop new compact, portable instrumentation to detect and measure acidic gases that could be generated.
|Chemical||Predicted Color Change||Reaction Chemistry|
|Sulfur dioxide||Violet to yellow||SO2 + pH indicator - yellow reaction product|
|Benzene||White to brown-green||C6H6 + I2O5 + H2SO4 - I2 + CO2 + oxidation products|
|Hydrogen chloride||Blue to yellow||HCl + Bromophenol Blue - yellow reaction products|
|Toluene||White to brown||C6H5CH3 + I2O5 + H2SO4 - I2 + CO2 + oxidation products|
|Carbon monoxide||White to brown||5CO + I2O5 + SeO2 / H2SO4 - I2 + CO2 + oxidation products|
|Hydrogen cyanide||Yellow to red||HCN + HgCl2 - HCl + Hg(CN)2 HCl + Methyl Red - reddish reaction product|
New, simple equipment was developed to detect and measure the acid gases- hydrogen chloride, hydrogen cyanide, and sulfur dioxide (see table at right). Additional chemicals of interest were carbon monoxide, benzene, and toluene. Drager tubes would serve as the "sensors" in the instrumentation. Color changes in the tubes can be examined easily after a test.
The new package used sorbent tubes in addition to the Drager tubes. These tubes generally are more accurate than the Drager tubes, but they show no color change and require laboratory analysis. Either real-time monitoring or a visual indicator like a Drager tube is needed to be sure that an experiment has produced the chemicals being studied. When both tubes are used, the Drager tubes can provide a coarse measurement while the sorbent tubes provide a fine measurement. Four types of sorbent tubes were used to measure sulfur dioxide, hydrochloric acid, hydrogen cyanide, and the b-tex compounds that include benzene, ethylbenzene, toluene, and xylene.
Both the Drager and sorbent tubes in this package require a constant gas flow to be delivered through the tubes, unlike the passive Drager tubes used in the first test. A system of pumps, flow controllers, tubing, and a valved manifold system supplied the air flow. Three pumps were required for each gas sampling package (Figure 1).
Figure 1-Schematic of the new gas sampling system used during the entrapment tests in California.
A 12-volt pump pulls a steady gas stream of 2 liters per minute into the system through 14-inch ID Tygon tubing. This pump was powered by a 12-volt Power Sonic rechargeable gel battery that had a lifetime of 8 hours under continuous usage. Excess gas flow is channeled to an exhaust port. From this main gas flow, two smaller pumps pull the required air flows through 18-inch Tygon tubing to either the sorbent tube sampling train or the Drager tube sampling train. The tubes in each sampling train were arranged in parallel. Each tube has specific flow requirements that are controlled by a valved manifold. The flow across each tube is set by its associated needle valve on the manifold. The pumps pulling flow across each sampling train also can be programmed to adjust flow control. This guarantees delivery of a constant preset flow rate if the inline Teflon filter collects a great quantity of particulate or if there is a minor blockage (such as pinched tubing) in the system. Once gas has passed through the sampling trains, the gas is channeled to the exhaust ports.
Outer packaging and a long-distance flow delivery system (umbilical) were needed to help the instrumentation survive the hazardous fire environment. The components of the system were mounted on an aluminum sheet that slid inside an old steel military surplus ammunition box. The system was oriented such that the box sits on its side in the field or when working with the interior components. A Swagelok bulkhead fitting provided the connection for interior and exterior tubing. The exterior PTFE Teflon tubing was 24 feet long. A soft ceramic sheath protected it from high temperatures. The sheathing must withstand temperatures as high as 1400 °C where it is exposed in the vehicle cab and shelter. The umbilical was supported by an aluminum pipe that extended from the cab, through the floor to the ground. A piece of aluminum over the end of the pipe protected the umbilical and interior tubing while allowing gases to freely enter the tubing.
The vehicles, shelters, and test instrumentation were deployed on June 5, 1996, for a prescribed burn scheduled that day. The vehicles and shelters were situated on the outer edge of a road near the top of a ridge. The hillside below the road had a 70% slope. The vegetation was primarily chamise and sage, fuels known for their volatile oil components. Some cut vegetation was piled in open or sparse areas near the road to provide a continuous fuel source and help create an intense, long-duration fire.
The gas detection system was deployed in a standard aluminum fire shelter and in the Ford Patrol. The umbilical was supported by aluminum pipes inside the vehicle cab (Figures 2 and 3).
Figure 2-Overhead view of the instrumentation positions in the cab of the vehicle. The aluminum conduit with wiring or tubing inside was fitted through these holes and served as support and protection.
Figure 3-Cutaway view of the gas sampling assembly inside the aluminum conduit in the cab of the vehicle, and underground.
The remainder of the umbilical stretched across the road to the gas sampling package, which was on the cut bank side of the road. The instrumentation was on the lee side of the vehicle and shelters with respect to the direction of the fire's expected approach. Before the fire, gas flow across each tube and across the whole train was calibrated. A BIOS dry calibration, piston-type flow meter was used for the calibrations. As close to ignition time as possible, the flow controller was programmed, the pumps were started, and the umbilical and gas box were buried.
The fire was ignited below the road at the bottom edge of the burn unit and swept up the slope to the vehicles and shelters. The fire was more severe and of longer duration than either Florida burn. Instrumentation survived the experiment with no damage. The shelters and vehicles also appeared to have sustained little if any damage. The gas sampling units were retrieved, the pumps were stopped, and the Drager tubes were examined. All the tubes except the hydrogen cyanide tube showed some color change. All experimental tubes were removed and capped. A postfire calibration test was run with another set of Drager and sorbent tubes. The Drager tubes were examined and the following results were obtained:
|Gases (parts per million)||Engine||Shelter|
These numbers are derived from calculations applied to concentrations taken from visual examination of the calibrated Drager tubes. New Drager and sorbent tubes must be used for each fire as the reagents are chemically changed, rendering further readings inaccurate or unreliable.
A second prescribed burn took place the following day. The same vehicles were used. No structural damage and very little cosmetic damage (a few paint blisters) had occurred to the vehicles during the first fire. The second site had a higher fuel loading that promised an even more intense and longer fire event. The shelters and vehicles were positioned next to the edge of a road crossing the burn unit as in the first experiment. This road was on the east side of the draw. Some vegetation was cut and piled in bare and sparsely vegetated spots below the vehicles and shelters to obtain a continuous fuel source.
The gas sampling instrumentation was deployed inside the Ford Patrol and standard aluminum fire shelter exactly as it had been the day before. After calibration and as close to the time of ignition as possible, new Drager and sorbent tubes were fitted into the equipment, the pumps were started, and the equipment was buried.
After the fire was ignited, a wind change prevented flames from engulfing the shelters and vehicles. Thermocouple data revealed that the temperatures during the June 6 burn were somewhat higher than during the burn the day before. Those temperatures also lasted longer, an important condition for thermal degradation of materials in the vehicles and shelters. After the fire, smoke continued to rise from the interior of the patrol. When the door was opened, thick, dense, black, sooty smoke billowed out of the cab. This smoke was very black and sooty compared to the brown smoke that had collected in the cab during the first fire. The inside panel of the driver's door was smoking. The synthetic materials on the door panel on the fire side of the cab appeared to be thermally decomposing. Other synthetic materials hidden under the hood may have been in a similar condition.
The Drager and sorbent tubes were collected and capped. A postcalibration test was performed on the equipment. All the Drager tubes except the hydrogen cyanide tube showed a color change. Results from the fire were:
|Gases (parts per million)||Engine||Shelter|
Because no color change was recorded in the hydrogen cyanide tubes for either field experiment, concentrations were zero or undetectable as measured by the Drager tubes. In both experiments, all chemicals other than hydrogen cyanide were detected in both the shelter and the vehicle. Concentrations were higher in the vehicle cab. The concentration of sulfur dioxide was slightly higher during the second burn. The concentrations of benzene, toluene, hydrochloric acid, and carbon monoxide all were significantly greater during the second burn, particularly inside the vehicle. Data from the sorbent tubes for both burns were negligible and unreliable because of pump failures.
The final field test was on July 24, 1996, in the Beaverhead National Forest near Dillon, MT. Two surplus vehicles, a 1955 212-ton, 6x6 Reo and a 1972 34-ton 4x4 (club cab) Dodge pickup, were positioned on an old logging road next to a windrow of lodgepole pine slash. Fire shelters were placed near the vehicles. The dry, densely piled slash and midsummer weather conditions would normally produce an intense fire with a long duration.
One gas sampling system was positioned inside the newer Dodge pickup while the other was placed inside the standard aluminum fire shelter. Some modifications were made to the gas sampling system. Teflon tubing in the umbilical was replaced to ensure the system's purity. Internal plumbing was changed so that one pump flow controller unit was pulling across both the Drager tube and sorbent tube trains. A temperature label was slipped inside the Tygon tubing to monitor gas temperature at the entrance of the gas sampling package. Check valves were added at strategic points to prevent backflows that could contaminate the system or sample tubes. New Drager and sorbent tubes were placed in the collection unit after a calibration test.
The windrow of fuel was ignited. The wind changed direction and flames did not engulf the sides of the vehicles and shelters as expected. Sooty, dark smoke did collect in the vehicle cabs.
After the fire, the boxes were retrieved, the tubes were removed and capped, the postfire flow calibrations were performed, and the Drager tubes were examined. The sorbent tubes were sent to the Clayton Environmental Laboratory for analysis. Each yielded the results shown in the two tables below.
Prefire and postfire calibration data indicated that the sorbent tubes still had flow problems. With such a problem, concentrations could be off by a factor of 10. Although concentrations may have been off, all test chemicals were detected by the sorbent tubes. The concentrations of benzene and toluene were the highest among the gases studied, whether they were measured by sorbent or Drager tubes. Gas concentrations were higher in the vehicle than in the shelter except for hydrogen chloride, where the difference was minimal and the concentrations were low.
This test had mixed results. Benzene and toluene appear in concentrations that are nearly as high if not greatly higher than concentrations produced in the California burns. Concentrations of sulfur dioxide, hydrochloric acid, and carbon monoxide were lower than those detected in the California field tests. Temperature data obtained from the thermocouples show that this fire had the longest duration. The temperatures peaked slightly below those of the second California burn but were sustained at higher temperatures for a longer time.
The concentrations derived from the field tests may underestimate the true chemical concentrations. Correction factors were made for the excess amounts of flow before ignition. It is impossible to visually judge when gases are no longer being produced at the end of the experiment. Air volume is measured to the time the system is stopped, whether that air contains gases or not. That may flush and dilute gases in the sample tube.
|Gases (parts per million)||Engine||Shelter|
|Gases (parts per million)||Engine||Shelter|
Many plastics, including those commonly found inside motor vehicles, can produce the chemicals detected in these field tests. The flash ignition and decomposition temperatures (Table 2) for some of these plastics are in the range of temperatures reached inside or near the cabs of the vehicles (Table 3) during the tests. Long polymer chains decompose in the presence of heat or flame, producing chemicals of lower molecular weights such as hydrogen chloride, hydrogen cyanide, and similar chemicals.
Smoke, ranging in color from dark brown to dense sooty black, accumulated in the cabs of all the test vehicles during each of the field tests. Even after the June 6 burn was over, the Patrol continued to generate this smoke. This provides some evidence that the smoke was generated from some of the vehicle's synthetic components. In the early stages of decomposition, styrene polymers and acrylonitrile-butadienestyrene (ABS) characteristically generate black, sooty smoke rich in aromatic polymers.
Table 1-Gases produced by seven plastics.
|Rigid polyurethane foam||yes||yes||yes||yes||yes|
Table 2-Flash ignition and decomposition temperatures for six plastics.
|Flash ignition temperature (°C)||Decomposition temperature (°C)|
|Acrylonitrile-butadiene-styrene||466 (self ignition)||300-400|
|Rigid polyurethane foam||310|
Table 3-Temperatures reached in the outside air, inside a vehicle cab, and inside and outside a fire shelter during three tests.
|Location||June 5 (°C)||June 6 (°C)||July 24 (°C)|
|Vehicle: Outside||1000||440||< 200|
|Vehicle: Cab ceiling||< 85||280||250|
|Vehicle: Cab floor||-||45||-|
|Shelter: Outside surface||430||300||150|
|Shelter: Inside surface||150||180||140|
|Shelter: Inside 2 inches AGL||150||< 80||40|
|Shelter: Inside 12 inches AGL||220||-||75|
Carbon monoxide can be produced as a byproduct of the thermal decomposition of many plastics. It is also a product of incomplete combustion and is produced in any wildfire. A portion of the carbon monoxide detected may have come from smoke produced by natural fuels. Sulfur dioxide may be produced by thermal degradation of tires. Some tires were undamaged during the first California burn but caught fire during the second. During the Montana burn, tires burned on the side facing the fire and smoked on the other side. Concentrations of sulfur dioxide were highest during both the California burns, even though the tires generally did not burn or smoke. Industrial processes in the state may have contributed to the concentration of sulfur dioxide. Baseline data before the experiment could have helped determine the ambient concentration of sulfur dioxide on the day of the burn.
The fire shelter contains no plastics to serve as a source for these chemicals. However, all chemicals except hydrogen cyanide were detected in the fire shelter. Hydrogen cyanide is a component of the adhesives used in the shelter. This chemical was not detected by the Drager tubes and was only detected in small quantities in just one experiment by the sorbent tubes. The proximity of the shelters to the engine may have contributed to concentrations of these compounds. The swirling winds may have transported the chemicals to the air near the shelter and mixed the gases there. Pinholes and pores in the shelter material may have allowed the gases to enter. Smoke may have gone under the fire shelters. This is unlikely because heavy chain weighing down the inside perimeter of the shelter appeared undisturbed after each experiment. The lowest concentration of all chemicals except toluene was recorded during the Montana burn, when the wind was moving the fire's smoke away from the vehicles. The questions raised by these results might be answered if an additional gas sampling unit were deployed inside the burn unit to measure ambient gases near the shelter and vehicle.
A special thanks to the Intermountain Fire Sciences Laboratory Fire Chemistry Research group, Clayton Environmental Laboratory, and the MTDC purchasing and shop personnel.
-Lynn Weger has worked on fire projects at MTDC since 1996. She graduated from the University of Montana with a B.S. degree in chemistry in 1987 and began working at the Forest Service's Intermountain Fire Sciences Laboratory the following year.
The following is the list of components used to assemble the gas sampling system.
|Diaphragm pump, 5x4x212 inches, 12 volt dc, 1.5 amps||KNF Neuberger, Inc.||Rechargeable gel cell battery, 734x412x214 inches, 12 volt, 8 amp hours||Power Sonic||Tygon tubing, large size 14-inch ID, 38-inch OD, 116-inch wall||Cole-Palmer||Tygon tubing, small size 18-inch ID, 14-inch OD, 116-inch wall||Cole-Palmer||HDPE fittings, high-temperature resistance, various shapes||Cole-Palmer||Manifold, 12-port black anodized aluminum||Clippard Minimatic||Brass needle valves, 10-32 male||Clippard Minimatic||Brass fittings (plugs, hose barbs, pipe to hose)||Clippard Minimatic||Teflon tape||Cole-Palmer||Alpha constant-flow air sampler||Dupont||Temperature labels||Omega||Drager tubes||National Draeger, Inc.||Sorbent tubes||National Draeger, Inc.||Teflon tubing, 0.190-inch ID, 0.250-inch OD, 0.03-inch wall||Cole-Palmer||Voltrex ceramic sleeve packing, 1 inch x 25 feet, 132-inch wall||SPC Technology||Bulkhead Swagelok fitting||Idaho Valve and Fitting||Aluminum plate 13x1678x14 inches||scrap||Steel surplus ammunition box, 1714x 758x1418-inch wall||scrap|
Drager organization. 1994. Drager-tube handbook. Gad, Shayne C.; Anderson, Rosalind C. 1990. In: Combustion toxicology. CRC Press: 147-192.
Gerstle, R. W.; Kemnitz, D. A. 1967. Atmospheric emissions from open burning. Journal of the Air Pollution Control Association. 17(5): 324-327.
Guastavino, Thomas M.; Speitel, Louise C.; Filipczak, Robert A. 1982. The pyrolysis toxic gas analysis of aircraft interior materials. Final report to the Department of Transportation. 33 p.
Huggett, Clayton; Levin, Barbara C. 1987. Toxicity of the pyrolysis and combustion products of poly(vinyl chlorides): a literature assessment. In: Fire and Materials. Vol. 2: 131-142.
Landrock, Arthur H. 1983. Handbook of plastics flammability and combustion toxicology. Noyes Publications.
Levin, Barbara C. 1987. A summary of the NBS literature reviews on the chemical nature and toxicity of the pyrolysis and combustion products from seven plastics: acrylonitrile-butadiene- styrene (ABS), nylons, polyesters, polyethylenes, polystyrenes, poly (vinylchlorides) and rigid polyurethane foams. In: Fire and Materials: Vol. 2: 143-157.
Madorsky, Samuel L. 1964. Thermal degradation of organic polymers. Interscience Publishers.
Miller, James A.; Fisk, George A. 1987. Combustion chemistry. Chemical and Engineering News: 22-44.
Nelson, Gordon L. 1990. Fire and polymers; hazards identification and prevention. Washington, DC: American Chemical Society: 542-565.
Paabo, Maya; Levin, Barbara C. 1987. A literature review of the chemical nature and toxicity of the decomposition products of polyethylenes. In: Fire and Materials. Vol 2: 55-70.
Paabo, Maya; Levin, Barbara C. 1987. A review of the literature on the gaseous products and toxicity generated from the pyrolysis and combustion of rigid polyurethane foams. In: Fire and Materials: Vol. 2: 1-29.
Ryan, Jeffrey V.; Lutes, Christopher C. 1993. Characterization of emissions from the simulated open-burning of non-metallic automobile shredder residue. Final report to the Environmental Protection Agency. 73 p.
Sarkos, Constantine P.; Hill, Richard G. 1988. Characteristics of transport aircraft fires measured by full-scale tests. Paper No. 467-11 from the Aircraft Fire Safety Conference Proceedings: 11-1 to 11-18.
Sarkos, Constantine P.; Hill, Richard G.; Howell, Wayne D. 1988. The development and application of a full-scale wide body test article to study the behavior of interior materials during a postcrash fuel fire. Paper No. 123 from the Aircraft Fire Safety Lecture Series: 6-1 to 6-11.
Terrill, James B.; Montgomery, Ruth R.; Reinhardt, Charles F. 1978. Toxic gases from fires. Science: 200 (4348): 1343-1347.
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The camera is a Sony SSC-DC30 with a threaded "C" mount that accepts various lenses. Lenses from 3.5 to 50 mm are available. This camera requires a 12- to 18-volt, 4.5-amp current and outputs a standard NTSC video signal.
The recorder is a Sony Hi8 camcorder (CCD-TR700). The camera portion of this unit is not used. The video signal from the SSC-DC30 camera is fed directly into the video tape recorder. The camcorder requires a 6.5-volt, 2-amp current.
One battery powers both units. The battery is a 14-volt, 5-amp-hour Gates Cell that is fused. The camera is powered directly from the battery; the camcorder uses an adapter to reduce the voltage.
The insulated box, made of 16-gauge stainless steel (Type 306), has tripod mounts welded on the bottom. The insulation inside the box is 1-inch thick ceramic board. This ceramic has a continuous- use temperature of 1260 °C. Its thermal conductivity at 815 °C is 0.95 BTU inches Hr °F Ft2.
The window for the camera is a thermopane design using Corning Vycor glass on the outside and a hot mirror on the inside. The Vycor glass is 96% silica and 4% boric oxide. It can be used continuously at 898 °C and intermittently to 1298 °C. This glass has a high resistance to heat shock. It can be heated to 900 °C and plunged into ice water without breaking. The inner glass is a dichroic mirror that transmits 90% of visible light (400 to 700 nm) and reflects 98% of the infrared light (wavelengths greater than 700 nm). The metal coating on the glass faces the outside of the box. This prevents radiant energy from heating the camera.
The Sony SSC-DC30 camera uses 4.5 watts of power. This will generate heat that raises the temperature inside the insulated box 0.0033 °C per second or 24 °C in 2 hours. The resulting temperature would be higher than the maximum recommended temperature of 52 °C. To keep the camera cool, 16 ounces of blue ice is frozen and placed under the camera mount. The power and video cables connecting the camera to the battery and recorder are routed through woven ceramic sleeving that is routed through steel conduit. The conduit is then wrapped with ceramic blanket (rated for continuous use at 1300 °C) and the assembly is wrapped with aluminized fire shelter material.
The camera must be within 5 to 10 feet of the subject. If the camera is farther away, smoke is likely to obscure the subject. The camera is mounted on the aluminum base plate, placed in the insulated box, and connected with a coax cable to the Tektronics waveform/video monitor. The Tektronics monitor becomes the viewfinder. The waveform is used to adjust the camera exposure. After the exposure has been adjusted, the monitor is disconnected and the camera is connected to the video camcorder/video tape recorder (VTR). The recorder can record for 2 hours.
2-Bolt the tripod legs to the box with 14-inch bolts. Insert the power cable and the coax cable into the box one at a time. Connect the insulated conduit to the bottom of the box.
3-Choose the camera location and set up the boxes. The wide-angle camera lenses allow the camera boxes to be within 5 to 10 feet of the subject. This is important because smoke can obscure the subject. Cameras inside vehicles must use the 3.6 mm Computar lens.
4-Mount the camera on the aluminum channel with a 14-inch flathead bolt. Connect the power cable. Connect the coax cable to "video out" using a rightangle BNC adapter.
5-The switches on the back of the camera are:
8-Connect the power cable to the battery. Connect the camcorder power cable to the battery and to the camcorder.
9-Connect the coax cable from the Tektronics monitor to the coax cable from the camera using a female-female phono adapter.
10-Turn on the camera and the Tektronics monitor. The PIX button shows the picture from the camera. The WFM button shows the waveform (exposure).
11-Focus the lens on infinity (the wideangle lenses do not focus). The lens mount must be adjusted by loosening the Phillips screw (LOCK) on the side of the camera and turning the lens thumbscrew on top of the camera. Use the Tektronics monitor (PIX) to view the picture.
12-The Computar lenses have two adjustments:
13-Disconnect the camera coax cable from the Tektronics monitor and plug it into the video jack (yellow) on the camcorder. Use a right-angle phono plug adapter. The CCD-TR101 has a switch that must be set to input.
14-Plug the remote control into the REMOTE jack. Then turn the camcorder power switch to VTR. The power switch on the remote can turn the power on or off only if the power switch on the camera is set to VTR. Insert a 120-minute tape. Look into the viewfinder to confirm that the video signal is coming from the camera. If it is not, check all power and cable connections.
15-Record some video by pressing the two REC buttons on the remote control. Rewind and play the tape. The remote control will show the counter running and a round dot will display, confirming that the camcorder is recording. The playback can be viewed in the viewfinder or by connecting the Tektronics monitor to the camcorder video jack.
16-Close the boxes and start recording just before the fire. Seal the camcorder box and the remote control in a plastic bag and bury them. Be careful not to depress any buttons when burying the remote control.
-Jim Kautz heads the Audio-Visual Support Unit at MTDC. He graduated from Montana State University in 1975 with a B.S. degree in film and television production. He worked in fire control positions and as a smokejumper before coming to the Center in 1976.
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Safety won't cost you anything...until you forget it. -Richard E. McArdie, Chief
Forest Service, 1953
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Missoula, MT 59804-7294
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