Clive M. Countryman

“ Some radiation problems can be alleviated Ordinarily, a piece of burning wood larger than about an inch in diameter does not continue to burn well or goes out if it is burning by itself and in a position where it can radiate thermal energy in all directions. The heat losses from radiation and convection are so great, and the heat conduction into the interior of the fuel so slow, that the flame at the surface cannot produce enough heat to keep the combustion process going. ”

“ Thus, the amount of heat transferred to the fuel by radiation from a fire depends greatly on the extent of fire or hot area the fuel is exposed to or can "see." A fire burning on one slope of a narrow ravine, for example, may expose the opposite slope to strong radiation and heating. This heat can dry the fuel and preheat it sufficiently to make it highly susceptible to ignition from sparks and embers. Occasionally, the radiation may be intense enough to ignite the whole slope, or a large part of it, almost simultaneously. ”

“ If you are caught in a wildland fire situation from which escape is not possible, your survival may depend on protection from intense radiation while the main flame wave passes. Possible temporary shelters include road cuts and cut banks, boulders, large logs, depressions in the ground, motor vehicles, and buildings in good conditions. Because fire and radiation intensity usually increase with fuel loading, refuge should be sought in areas where the fuel is as sparse as can be found. ”

“ Radiation and wildland fire Before a wildland fire can start, heat must be transferred from a firebrand to the fuel. Then heat must be transferred from the fuel surface to deeper layers if the fire is to continue to burn. Finally, heat must be transferred to surrounding unburned fuel if the fire is to spread. And decreasing or eliminating heat transfer is about the only way we have of controlling and extinguishing a fire. ”

“ Fire spread by radiation usually tends to be slow. As we have seen, radiation intensity decreases rapidly with distance, so fuels more than a short way from the flames are heated slowly and are not likely to ignite until the flames approach them closely or until they have been exposed to radiation for a considerable time. Also, radiation travels only along straight lines, so that often much of the fuel is shielded from direct radiation by other fuel until the flames are close. ”

“ The ground and other solid materials are better radiators than air, and lose heat more rapidly, especially dark-colored materials. Consequently, the solid materials become colder than the surrounding air. This is why frost may form on exposed surfaces, particularly dark ones, when the air temperature remains above freezing. ”

“ A snag in front of an advancing fire may also ignite in an unexpected way from the effects of radiation. Because of the shielding action of low-level fuels, the upper portion of the snag is likely to be exposed to radiation longer, and often to greater radiation intensity too, than is the lower portion of the snag until the fire approaches it closely. Thus, the snag may ignite first at some point well above the ground, either from radiation directly, or because preheating and drying permit easy ignition by flying sparks and embers. ”

“ If time permits and no better refuge exists, scoop out a narrow trench and lie in it. Always cover exposed skin and keep your face close to the ground where the air is cooler and more free from smoke. ”

“ Heat transmitted by radiation across a control line can preheat and dry fuels, making them more susceptible to ignition, or igniting them directly. Some topographic configurations facilitate preheating and drying of fuels by increasing the hot area the fuels can see, and this may result in ignition of large areas at one time. ”

“ Under windy conditions or on steep slopes, heat transfer by convection is likely to be most important. But with light winds and gentle terrain, the fire convection column is nearly vertical, and radiation becomes the major method of heat transfer. ”

“ But do not attempt to escape if there is little chance of success—you may make your situation worse. By keeping calm and making maximum use of the available opportunities to protect yourself from heat, you can greatly increase your chances of survival. ”

“ Firefighters working along an actively burning fire are exposed to heating from radiation. The effects of radiation can be reduced through the use of proper clothing. Heavy cotton or wool is preferable to other common fabrics, and two layers of clothing are better than one. ”

“ But when several pieces of fuel are close together, the heat losses are greatly reduced—each burning piece supplies heat to others—and the fuel can burn intensely. This is why a single log in a fireplace can seldom be made to burn, but three or four logs together burn well. ”

“ Although most structures are likely to catch fire in a critical situation, usually they do not do so immediately, and the fire buildup is often relatively slow. Thus, the main flame wave will probably have passed by the time the heat in the building becomes intolerable. ”

“ Contrary to general belief, it is improbable that the fuel tank win explode and quickly engulf the car in flame, even after the car is burning. Experience and tests indicate that a sound fuel tank will usually remain intact in a burning car.
Buildings can sometimes be used Temporary shelter can also be found in or behind buildings that are in good condition and not easily ignited, particularly where the surrounding fuel loading is not heavy. ”

“ Motor vehicles can provide shelter Cars and trucks can provide good temporary shelter. Move the vehicle to bare ground or to as sparse fuel as possible. Close the doors and windows, lie on the floor, and cover yourself with a coat or blanket. ”

“ Avoid flimsy, unpainted wooden structures—they ignite easily and burn hot and fast. Wooden buildings in heavy fuels are also a poor choice because of the length of time a hot fire persists in such fuels. ”

“ For example, more than 80 percent of the body's cooling capacity is utilized when a firefighter is working 6 feet away from flames about 1 foot high. With flames 2 feet high this capacity is exceeded at the same distance. ”

“ The effectiveness of these temporary shelters can be greatly increased by some fireproof covering, such as the shelter tents issued to most fire crews or the asbestos cloth blankets usually carried in firefighting equipment. A dirt covering can also help. The airflow in a fire front is often strong and turbulent, so any lightweight covering must be adequately secured. ”