PYRAMIDAL ROOFS

BY FRANCIS L. BRANNIGAN, SFPE (Fellow)

A pyramidal roof support is made up of short light-steel sections in a space frame, a three-dimensional truss. If fire is in the roof, the lightweight steel sections will become distorted. Undesigned torsional forces will be generated in all directions; the effect on the total roof will be unpredictable. You must use the thermal imaging camera if fire is in the roof void unless full sprinkler protection is installed. If sprinklers are out of service and the fire should reach the roof void, abandon interior operations because these conditions are very hazardous for firefighters.

When preplanning, consider the following:

  • Is the building sprinklered? Do the sprinklers extend to the roof void? A fire in an unsprinklered roof void will spread rapidly on the plywood or chipboard (oriented strand board).
  • The void space may be used for lightweight storage.
  • The ceiling grid may be suspended from the space frame or from screw eyes in the plywood. In either case, a roof fire could cause the ceiling to fall, trapping firefighters in a net-like grid. One firefighter casualty in the Houston, Texas, Mc-Donald’s restaurant tragedy was found with wire cutters near her body. Wire cutters will not be adequate to cut a firefighter out of the net.
  • Often, the trade applies the undefined term “fire rated” to lay-in ceilings, but the rating in this case refers to flame spread, not fire resistance.1
  • The building code may have required a gypsum ceiling as a short-term barrier to a contents fire extending to the void. Such a ceiling is not at all equal to rated gypsum board and wood assem-blies. If the fire starts in the void or extends into it, the gypsum ceiling and its supports will be a barrier to hose streams and present a collapse hazard.
  • If the building is sprinklered, back up the sprinklers to the maximum as soon as possible, probably even before stretching a handline. The following quotes are appropriate:

•”No building is worth a firefighter’s life.” (Vincent Dunn, Fire Department of New York)

•”We will not risk our lives at all in an attempt to save lives or property that is already lost.” [Alan Brunacini, Phoenix (AZ) Fire Department]

Some traditionalists abhor “writing off” a building despite serious deficiencies. For them, this suggestion-not a recommendation-is offered: Any personnel working on the roof should be supported independently, as on a tower ladder (or ideally with an articulating boom). Ven-tilating the roof will increase the fire’s intensity, so be prepared for a burst of fire when the roof is opened. Be ready to sweep the entire inside surface of the roof with heavy smooth-bore streams. This is not really possible from one hole because of angles. Two tower ladder crews coordinated to open both holes simultaneously might be able to kill the fire in the roof.

ANOTHER CLOSE ESCAPE

Thanks to Lieutenant Jay Moltenbrey of the Windham (NH) Fire Department, we have another incident in which a thermal imaging camera (TIC)-the firefighter’s radar-helped to get firefighters out before a collapse. At 1:30 a.m., his department responded to an unusual structure (a building that is one story in the front and two stories in the rear). An occupied Dunkin’ Donuts was in the front. Smoke was coming up through the floor. The firefighters went to the back and forced entry to several stores on the lower level. There was a medium level of smoke in the stores. Moltenbrey was using the thermal imaging camera to try to locate the fire. He found heavy fire in the overhead and ordered evacuation. As personnel were evacuating, the suspended grid and panel ceiling fell. A Salem (mutual-aid) captain was tangled in the wires that supported the ceiling. He used his surgical scissors to cut the wire and escaped. The burning trusses collapsed shortly thereafter. In the past, the practice would have been to pull the ceiling, adding oxygen to the smoldering fire in the void. Many times, the result has been a flashover.

I suggest using a piercing nozzle to cool down the gases in a void before admitting oxygen. Moltenbrey pointed out the following: Two parallel walls may “blend into one” and appear as one wall through the camera lens. The TIC operator should practice with the camera and become aware of any characteristics that may be confusing.

HIDDEN HAZARD

In 1951, I observed a fire in a strip mall. A store at the end had been forced, examined, and found to be clear. It was clear when I looked in. As I entered, the paint on the pressed steel (so-called “tin”) ceiling started to smoke.2 The paint then turned brown and started to burn. Flaming paint set fire to the flammable contents. This all happened in less than a minute. Fire was raging overhead; it was completely hidden and went unnoticed. Today, we have the TIC, which can show you the deadly fire overhead. It may soon be deemed “reckless disregard of human life” to permit firefighters to enter a building involved in fire without a TIC to detect hidden fire.

A SERIOUS ELECTRICAL HAZARD

My niece is an EMT studying to be a paramedic/firefighter. At a recent serious fire in a wooden house, the ladder truck was parked under the charged electrical service wires. She recognized the hazard of the charged wires burning off the building and dropping on the truck. The truck was moved. Incidentally, are all your troops aware of the probable fatal consequences of stepping off the truck in such conditions? Wait until the electrical service is killed. If you must move off the truck, jump off. In the Atomic Energy Commission, we had more fatalities resulting from a crane’s hitting overhead electrical service than from radiation.

Endnotes

  1. In some rated floor and ceiling assemblies, the tiles in the lay-in tile ceilings are part of the fire-resistance system as tested. See Building Construction for the Fire Service, Third Edition (BCFS3), pages 293-299, for a detailed discussion of the deficiencies of such installations.
  2. Metal ceilings were required by codes developed by people who knew steel was not combustible but who did not recognize the conduction characteristic.

FRANCIS L. BRANNIGAN, SFPE (Fellow), recipient of Fire Engineering’s first Lifetime Achievement Award, has devoted more than half of his 60-year career to the safety of firefighters in building fires. He is well known for his lectures and videotapes and as the author of Building Construction for the Fire Service, Third Edition (National Fire Protection Association, 1992). Brannigan is an editorial advisory board members of Fire Engineering.

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