Protecting exposures

BY BILL GUSTIN

Protecting exposures is second only to rescue in firefighting priorities. Ideally, the best way to protect ex-posures is to put the fire out be-fore it can spread to adjacent structures. This, however, may not be possible when the fire has already spread to exposures or when there’s more fire than firefighting resources. Rural and suburban fire departments face this problem when they arrive on a rapidly spreading fire with insufficient personnel and not a hydrant is in sight.

SIZE-UP FOR EXPOSURE PROTECTION

The key to effective exposure protection is an ongoing size-up that accurately assesses fire suppression resources against the potential for fire to spread and the threat it poses to life and property. A size-up is extremely important when more than one exposure is threatened and fire officers must prioritize which one to protect first. An accurate size-up is also essential in choosing the most appropriate strategy.

Offensive Mode

When resources are sufficient, fire officers generally choose to operate in the offensive mode by rapidly attacking a fire from inside a building before it can spread to exposures. This is the way most fires are attacked in big cities. Big city fire departments usually have the resources to apply thousands of gallons of water on a fire within a few minutes after it is reported. This is because of a rapid response, large numbers of personnel, and generous spacing of hydrants capable of supplying substantial flows of water. Additionally, big city fire departments have sufficient companies to simultaneously protect exposures if they are threatened or are already involved and direct a massive exterior attack on the main body of fire. This is seldom the case for rural and many small suburban departments that can easily find themselves overwhelmed by a large, rapidly spreading fire.

Defensive Mode

When resources are insufficient, they will be used most effectively by operating in the defensive mode, protecting exposures and allowing the fire building to burn. For example, a three-firefighter engine company arrives at a well-involved wood-frame house that threatens adjoining frame homes on each side. To make matters worse, there are no hydrants in the area, and the second-due engine is still six minutes away. The officer has to decide how to make the most of the water in the apparatus booster tank. He could choose to empty his tank with a brief, high-volume attack on the main body of fire. This “blitz attack” is a viable option, but if it fails, the fire will reintensify and spread unimpededly to the exposed homes.

  • Use water sparingly. A better tactic may be to advance two 13/4-inch preconnected handlines and operate them sparingly on the sides of each exposure. This, however, requires a company officer who gives strong explicit orders and disciplines firefighters to follow them. Otherwise, put a nozzle in the hands of a young, excited firefighter, tell him to apply water to an exposure, and watch what he does. There’s a good chance that he will give in to an almost irresistible desire to direct his stream into the main body of fire (I know, I remember doing it myself). This is no time to waste water, but it is as if the fire were a powerful magnet, attracting and vaporizing all but the heaviest high-flow streams uselessly into the air. Firefighters operating in the defensive mode will use what little water they have most effectively by opening their nozzles intermittently, just enough to keep a film of water on exposed surfaces. This will prevent temperatures from rising above 212°F, the boiling point of water. Remember, it takes less water to keep combustibles from igniting than it does to extinguish them once they catch fire.

When water is plentiful, opt for the 21/2-inch handline for exposure protection.

  • Use Class A foams. Fire departments can enhance the thermal protection properties of water by proportioning Class A foams into their hoselines. Class A foam solutions protect exposures better than plain water because they reduce its tendency to run off vertical surfaces. Foam helps water penetrate and cling to exposed combustibles, thus maintaining protection for a longer period of time. Foam requires less frequent reapplication, which is extremely valuable when water is limited.
  • Direct water streams into the main body of fire. This defensive exposure protection tactic involves directing streams into the main body of fire. In this case, the intent is not to extinguish the fire but to push it back into the fire building, away from exposures. This is accomplished by directing aerial and ground-operated master streams into windows or through the roof of the fire building. Handlines can also be used for this purpose. When using handlines in this fashion, they are most effective when operated from a “point of vantage”-that is, hoselines are stretched into an exposed building and operated from the roof or out of a window into the fire building.

So, basically, firefighters can protect exposures by putting water directly on the fire, on the exposures, or a combination of the two. At this point, someone is bound to ask the question: What about spraying water in the space between the fire and exposures? This was a widely accepted practice years ago. In fact, some departments still carry homemade and factory-built “water curtain” unmanned appliances that produce a fog pattern or broken stream between a fire and exposures. Most of these relics have become museum pieces because we have learned that water, being transparent, is a poor barrier to radiant heat. We now know that water’s heat absorption capability is maximized when water reaches its latent heat of vaporization. And, this is most effectively achieved by applying a stream to a fire in quantities sufficient to absorb heat faster than it is being generated or by applying water in lesser quantities to exposed surfaces, preventing temperatures from rising above their ignition temperature.

Removing the Fuel


(1) Operating handlines from the “point of vantage”-from an exposure onto the fire-helps to keep the fire away from the exposures. (Photo by Mike Heller, 911 Pictures.)



Finally, there is an exposure protection tactic that does not require water application at all. If water is not available to reduce the heat, perhaps you can remove the fuel in the path of a spreading fire. This was recently done in my response district when a trailer park containing 400 closely spaced old mobile homes was closed and all of its residents were evicted. This became the site of several fires, presumably set by angry residents of the trailer park or demolition workers wanting to speed up the wrecking process. The potential for a conflagration was great because ambitious scavengers made quick work out of stripping the sheet metal off the sides of virtually every mobile home, leaving a “lumberyard” of frame shacks consisting of 2-inch 2 2-inch studs and particleboard sheathing.

At one fire, our battalion chief ordered the demolition company to use its bulldozers and backhoes to tear down trailers in the path of the spreading fire, cutting off its fuel supply. Also, heavy equipment is frequently used at large tire and scrap yard fires to dig “firebreaks,” thus keeping the fire to a manageable size.

Firefighters, themselves, can remove fuel exposed to fire when they enter an exposed building and remove curtains from windows facing the fire.

SETTING PRIORITIES

When fire is spreading to more than one exposure, firefighters must decide where to concentrate their efforts. Clearly, structures nearest the fire building are at great risk, but sometimes proximity alone must become secondary when a more distant exposure has a greater life hazard. Take, for example, a large complex of garden apartments in the framing stage of construction. Although this is a conflagration waiting to happen, those buildings may have to be sacrificed to protect a nearby assisted living facility full of elderly residents who can’t possibly be evacuated.




When setting priorities for exposure protection, also consider wind direction. Exposures downwind of a fire are more susceptible to wind-driven fire and flying brands than exposures upwind. Determine the combustibility of exposed surfaces. Frame walls covered with asphalt shingles and wood shake shingle roofs have been factors in many devastating fires. If all other factors are equal, a wall with window openings will be more vulnerable than a solid wall without openings, especially if it is of masonry construction. Building height is another important consideration. For example, a two-story building is in much greater danger from fire burning through the roof of an adjacent one-story building than if both buildings were of equal height.




(2) First-arriving firefighters find a wood-frame house shrouded in heavy smoke because the fire is deprived of oxygen. Firefighters must accurately predict fire spread and intensity so exposures can be covered before they are endangered. (Photos by John Ferraro.) (3) As oxygen is introduced, the fire suddenly “lights up.” Firefighters scramble to protect the adjacent frame/stucco house and apply a cooling stream to the apparatus. (4) The frame/stucco house is exposed to fire and begins to “steam,” producing telltale vapors barely visible as gray-white smoke. This is a sure sign that ignition is imminent unless a cooling stream is applied to heated surfaces. (5) The first handline is directed on the exposure, stopping the formation of the telltale vapors.

Look out for hazardous materials. Buildings and containers that store toxic, flammable, or explosive materials may require cooling streams before closer, more threatened exposures.




Finally, when setting priorities, watch for exposed surfaces that are producing telltale vapors-a sure sign of impending ignition. When combustibles are heated, moisture in the form of water vapor is distilled first, followed by flammable vapors produced by thermal decomposition. Telltale vapors ignite and propagate with the speed and intensity of a gas-fueled fire because, essentially, that’s what it is. Telltale vapors are recognized when exposed surfaces begin “steaming”-that is, producing gray-white vapor or light-colored smoke. These surfaces demand the immediate application of a cooling stream of water before they suddenly burst into flame. Size-up is the key; determine your priorities before you start putting hose on the ground.

PREDICTING FIRE SPREAD

Incident commanders must predict the progression of fire and then determine the need for exposure protection with cautious, pessimistic anticipation. As a practical matter, this means where will the fire spread and how big will it be by the time that hose is on the ground and water is flowing on exposures? If you have the slightest doubt that your offensive, interior attack will be successful, call for additional companies to set up heavy, defensive streams on the fire building and exposures. Hopefully, they won’t be needed; yes, some “kitchen chief” may say you overreacted by calling for an additional assignment you didn’t need. But, this is a lot better than underreacting, miscalculating fire spread, and having the fire outrun your position. You must be proactive. Don’t expect firefighters who are driven out of a building to rapidly set up and operate a defensive attack. Defensive positions must be set up in advance, in anticipation of the fire’s getting away from you.




Consider also the intensity of the fire once windows fail and oxygen increases, the roof burns through, or the walls collapse. Storefront show windows are particularly dangerous. Hot, black, sooty, or cracked glass is getting ready to fail, which will create an inrush of oxygen and an outflow of heat and flame.

Remember that your apparatus can be an exposure, too. Don’t burn up a $400,000 rig by placing it too close to a building that’s probably worth much less and, incidentally, is losing value rapidly!

Finally, don’t forget that your most critical exposure, second only to civilians, is firefighters. They must be positioned out of harm’s way and never be unduly endangered just to save property.

BILL GUSTIN is a captain with the Miami-Dade (FL) Fire Department (formerly Metro-Dade) and lead instructor in his department’s officer training program. He began his 28-year fire service career in the Chicago area and teaches fire training programs in Florida and other states. He is a marine firefighting instructor and has taught fire tactics to ship crews and firefighters in the Caribbean countries. He also teaches forcible entry tactics to fire departments and SWAT teams of local and federal law enforcement agencies. He is an editorial advisory board member of Fire Engineering.

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