By JOHN NORMAN

One of the most difficult decisions a fire officer must make on the fireground is when to abandon the firefight and order the evacuation of the fire building. No firefighter wants to surrender too early, for the lives and property of the community we serv e is being attacked. We fight the enemy with everything we've got to preserve both life and property.

Yet firefighters cannot delay too long in evacuating or else it can be their lives that are lost. What is needed is a clear understanding of just how long we have to safely operate before conditions overpower us. Easier said than done!

Fire within a structure is a very dynamic affair, constantly changing. As firefighters we must constantly be aware of what the fire is doing around us. The fire is like a living creature, it moves, it breathes oxygen, and it can sneak up and bite us on ou r behinds if we're not careful.

The greatest threats to firefighters at a structure fire are flashover, backdraft and collapse. We must all study and attempt to recognize the warning signs for each of these events at every building we go to. If we recognize that one of these life-threat ening events is becoming imminent, we must take steps to prevent it, or else get everybody out of the danger area. In order to do this we must understand each phenomenon.

A fire inolving a vacant building that has had previous fires. With no apparant life hazard, firefighters are positioned outside of the collapse zone and heavy caliber streams are utilized. Handlines were stretched i nto the adjacent exposure to the right of the photo. Photo by Harvey Eisner

Caught In A Flashover
Flashover occurs at every working fire, usually prior to our arrival, which reduces the risk to us. It is characterized by free-burning flame, accompanied by large quantities of smoke, and rising levels of heat. In the past, before self-contained breathin g apparatus (SCBA) and encapsulating clothing (bunker gear and hoods), few firefighters were ever caught in flashovers because the smoke and/or heat drove them from the area before the room flashed over and engulfed the entire contents as well as occupant s in flame.

I have been caught by a flashover while conducting a search for an occupant that I was positive was still in the apartment. I survived by crashing through a window to which the ladder company crew just happened to be raising a portable ladder (Thanks, guy s!).

It is very easy to become fearless when the prospect of a definite (or even a suspected) trapped victim exists. Your body is keying on sounds of a potential victim, listening for moaning or gasps of breath, and you tend to "tune out" the warning signs the fire is sending, the rising heat levels, the tongues of flame overhead, the "snap, crackle, and pop" of the fire in this rapidly escalating phase. Don't!!!

The fire is telling you something. "Get out!" is what it's saying. You have to carefully evaluate whether the victim can still be alive under these conditions with no SCBA or protective clothing (the only thing that has gotten you this far) and, more impo rtant, whether you will be able to remove the victim to a safe area before the room lights up.

We are not in the business of crawling into a room to die alongside somebody who is already dead! Unless there is a suspected life hazard, firefighters should enter the immediate fire area only with a charged hoseline. If a suspected or confirmed life haz ard exists, do your search while constantly evaluating what the threats to your survival are, always being aware of at least two escape routes.

Warning Signs Of Backdrafts
Backdrafts are low-order explosions that result when we admit air into an enclosed area where the fire has previously consumed most of the oxygen. This explosion can have several life-threatening consequences. We can be hit with a ball of flame, concussio n, flying glass and debris, and the blast can cause collapse of all or part of the structure.

If we recognize the warning signs of a potential backdraft (very high heat conditions with no visible flame, very heavy brown/yellow smoke pumping under pressure, smoke "puffing" from the building and then being drawn back into the building, air being dra wn violently inward as a building is opened at lower levels) we should, if possible, take steps to prevent the occurrence of the backdraft, or at least, to prevent our people from being caught in the effects of the explosion.

We should try to alleviate the potential explosion by venting the highly heated gases out through the top of the space before any openings are made in the lower levels. That is possible only where the fire is directly below the roof level. If the suspecte d backdraft occurs, for example, in the ground floor store of a two-story building, then venting the roof will not prevent the backdraft when the front door is opened. Under these circumstances, an indirect attack made with a 30-45-degree fog pattern thro ugh a very small opening in a window, door or security gate may cool the explosive gases to below their ignition temperature.

If the indirect attack is not possible, or even it is has been applied, the next step is to make another opening with all members withdrawn to an area that is outside the path of the explosion and any subsequent collapse. Then go ahead and let it blow. Structural collapse is the most difficult of the firefighter traps to predict. There are a few good rules of thumb that may be useful, but they require a good bit of caution in applying them. They all should rely on the experience and observation of all t he members on the fireground in their application.

The most common structures that we operate in, houses and other residential occupancies, as well as many smaller commercial buildings, are most often either wood-frame or brick-and-wood-joist (ordinary) construction. These buildings were built with relati vely large floor and roof joists, typically two-by-eight-inch and larger. The 20-minute rule of thumb applies to this type of construction: If the fire is not under control in 20 minutes, you should probably begin withdrawing your personnel and shift to e xterior operations. Of course, this is only a guide and even as such it must be applied carefully and with some modifiers.

An important item to understand is that the time frame does not start with your arrival at the scene, or even with the receipt of the alarm, but when the fire has begun attacking the structural elements. Look for signs of advanced fire, such as fire on se veral floors, or fire burning through a wooden wall, which would indicate the fire has been burning for a considerable time prior to your arrival.

Also, try to be aware of the history of the building. A building which has had several fires in the past has suffered increasing damage and has only a limited time left before collapse. The same may be true of a building in which extensive renovations hav e been done, which have weakened the original structure.

If there is no outward indication of any of these situations, a standard interior attack is in order. If it does not succeed in a timely fashion, the incident commander (IC) must evaluate why. If the first attack crew exits the building after expending 30 -minute air cylinders and their officer reports the main body of fire knocked down, you have to make a decision. Do you continue interior operations or shift to exterior?

If your evaluation of conditions is that the attack crew's report is correct, the main body of fire is knocked down, then continue with the operation. On the other hand, if your overall perception is that there is still a considerable body of fire present that the interior crews have not put out yet, you have the responsibility to order them out. This is the most important decision that you will make. Only the IC can make it, based on reports he is getting from the various sectors. You must be able to tru st the observations of your subordinates to accurately report conditions in their area, but you are likely to be the only one with "The Big Picture."

I recall operating with my engine company, knocking out a lot of fire on the first floor, when we were ordered out of the building. We were doing a great job, making a lot of headway, and reported that back to the IC, "Just a few more minutes, Chief, we g ot it." The chief sounded rather agitated when he repeated his order to "Get the hell out here. NOW!" Imagine our surprise when we exited the building to find the top three floors blazing merrily away. When you're ordered to retreat, follow the orders.

The 20-minute rule of thumb is, as I said, good only in standard wood-frame or brick-and-wood-joist buildings. It is far too long to operate in any type of lightweight-wood-construction building. Buildings which were constructed using plywood I-beams, two -by-four gusset plate trusses, or the composite steel and wood trusses have all been proven to collapse with as little as five minutes of fire exposure.

A good listing of all buildings in your area that are built with these techniques is critical to firefighter survival. Also critical is a clear department policy that states that a fire that has reached the flashover stage in one of these structures will be fought only from defensive positions until the fire has been knocked down, and ventilation and lighting conditions permit a careful examination of the structural elements that are trying to fall down on top of us or out from under us. The same rule sho uld apply to the heavier wooden bowstring trusses (which I have seen fall down in as little as eight minutes after the fire reached flashover) and even seemingly heavy steel trusses. Unprotected steel can be expected to fail in as little as 15 minutes in a serious fire.

One of the most common structures today is the strip mall built with steel bar joists and metal deck roofs. A serious fire in one of these structures should be expected to produce roof collapse in as little as five to 10 minutes. As such, they too should be attacked from defensive positions. Steel does have one advantage over wood trusses, in that if the steel can be cooled with hose streams, it will retain and even regain its strength. It is possible to fight a fire in a row of strip mall-type stores by getting hose streams ahead of the fire and sweeping the steel with the stream while ladder company members vent, and check for extension.

Fires in heavy-timber structures usually are not an immediate collapse threat. The massive size of the timber elements allows them to burn for quite some time before they fall down. Usually, the massive fire that they produce, if not extinguished early, c hases the firefighters back out of the collapse zone. The exception to this involves vacant buildings that have been the scene of several smaller blazes, or one that has been vandalized or is in the process of demolition.

Class 1 (fire-resistive) buildings typical of high-rise construction usually are designated as having three- or four-hour fire resistance ratings. In the past, that was taken to mean that they would never be a serious collapse threat. While this is usuall y the case in the completed structures, it is not a guarantee, particularly in the steel-framed high-rise that relies on some type of spray-on or membrane fireproofing to protect the steel. The 1 Meridian Plaza fire in Philadelphia proved that these can b e severe dangers under the wrong set of circumstances.

The poured-concrete-skeleton-type of Class 1 building is much more resistant to large-area collapse under all circumstances except one: during the construction phase, when fire involves the wooden formwork used to support the wet concrete until it hardens . As Professor Frank Brannigan has pointed out in his momentous work, Building Construction for the Fire Service, this particular fire can cause total failure of the structure. The only safe way to deal with this incident is from safe defensive positions.

When deciding whether to commit troops to an interior attack in the first place, or whether to pull them out of an ongoing effort, the primary mission of the fire service must come clearly to mind. To protect life and property. It is always life first, in cluding firefighters lives. Property can always be rebuilt, your people can't.

Be constantly aware of what is happening to the building. Look for signs of structural weakness and/or alterations. Remember the time frames that you have to make a difference; they are set by the structural engineer that designed the building, not by you r desire to save the structure. One of the primary indicators of an impending collapse is the elapsed time from flashover. Bring all your people home safely!