CARBON MONOXIDE IN VOID SPACES
The generation and accumulation of carbon monoxide (CO) in void spaces is not as well recognized in the fire service as it should be.
Carbon monoxide is both toxic and explosive. For most toxic materials the dose received equals the exposure level (concentration) times the exposure time. A good rule of thumb is that any exposure in which the concentration (parts per million) x time (minutes) — 35,000 is likely to be dangerous. According to the NFPA’s Fire Protection Handbook, a 10-minute exposure to 3,500 ppm of CO would be hazardous and possibly incapacitating. Higher ppm values are even more dangerous. 12,500 ppm can be fatal after a few breaths.
The flammability range for CO is from 12.5 to 74 percent. Its ignition temperature is 1,128°F. When the ideal mixture of CO in air is present, a detonation can result sufficient to blow a building apart. Generally a deflagration —a huge, sudden blast — occurs.
In December 1989, 16 lives were lost in the John Sevier Retirement Home fire in Johnson City, Tennessee. Researchers for the Center for Fire Research-NIST examined the circumstances and determined that the deaths were caused by CO generated in a ceiling void. The old original combustible tile ceiling was left in place when the newer ceiling of flame spread-resistant tiles was installed. K. Sleekier, J. Quintiere, and J. klote, the researchers, stated, ‘‘The rapid involvement of a large, combustible surface combined with a restricted air supply alters the fire chemistry to increase CO production as much as 50 fold over burning in the open.” (In October 1989 NIST presented a proposal for a five-year research project into the production of CO. The thrust is on toxicity, not explosiveness.)
The very serious hazard of new ceilings below old combustible tile ceilings is covered in Chapter 9 of Building Construction for the Fire Service. It is a very serious hazard to occupants and firefighters alike, but it apparently is ignored by building departments. I am not aware of any building department that requires the removal of an old combustible tile ceiling when a new ceiling is installed. Two firefighters dies in Wyoming, Michigan when fire burst out of the ceiling. Even then the city did not amend the code.
ITie ignition of combustible gases accumulated in voids within the building may provide the fuel for a devastating explosion, even though the building is vented in the accepted manner.
At a stable fire in New York in 1938,1 witnessed an explosion of CO that had accumulated in void spaces. The violent explosion took place an hour and a half after the first alarm. It was presignaled by dense clouds of “boiling black smoke.” A longtime buff told me, “It’s going to blow.” The blast caused the collapse of a side w all and the loss of one officer’s life.
There was actually a detonation. Apparently the gas-air mixture was just in the right proportion. The building had been vented according to standard procedures. Unfortunately it was just unacceptable to the investigating committee that a backdraft explosion could occur 1 ½ hours after the first alarm in a vented building. The committee refused to believe that an explosion had taken place and held that the wall simply collapsed.
In 1946 New York City firefighters were battling a fire in an abandoned icehouse. Gas accumulated in a ninefoot cockloft and exploded. The back wall came down on an apartment house at the rear. Thirty-nine people watching the fire from fire escapes were killed. If the 1938 experience had been properly analyzed, perhaps the buildings would have been evacuated. (See “The Menace of Abandoned Buildings,” Fire Journal, January 1965.)
More recently I observed a fire in a row of stores. A combustible ceiling was mounted on wooden stringers. The void was about three feet deep. The building was vented; the store’s front window was completely out. There was bright fire that was suppressed w ith hose streams. The wind shifted. Heavy black smoke boiled out. Like the oldtimer mentioned above, I said to a companion, “It’s going to blow.” It did. Fortunately, the firefighters were just knocked down.
Suspended ceilings of combustible tile form void spaces in which fire can burn undetected until it bursts out furiously. In 1956 11 people died in Anne Arundel County, Mankind when fire involved the attic above a combustible ceiling in an amusement hall. The raging fire overhead did not appear to be serious. (See Fire Journal, September 1984, page 15. Combustible tile ceiling on stringers below a wood truss roof formed a void in which fire burned undetected.)
Firefighters and even some people in the truss industry are properly concerned about the structural stability of trusses in a fire. I am not aw are of too many people w ho join me in concern for the carbon monoxide generated in the truss lofts between the floors. Backdrafts from voids created in the rehabilitation of old tenements are quite common and should be expected from truss lofts. —Francis L. Brannigan lofts.
