Editor's note: This article finishes summarizing a small portion of the 79-page Chapter 2, "Principles of Construction," of the 667-page third edition of Building Construction For The Fire Service, by Francis L. Brannigan. Part 1 was published in Firehouse® in February 1996, part 2 in July...
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In the meantime, please READ and HEED Chapter 12, "Trusses," in Building Construction For The Fire Service, third edition. Particularly note the "Tactical Consideration" on page 532, "It cannot be stressed too often that heavy fire conditions can exist in concealed spaces, particularly overhead, and not be evident in the space below," and the four pages of "Tactical Considerations" beginning on page 557; senior officers might be well advised to READ and HEED the last paragraph of the "Tactical Considerations."
Earlier in this series, I pointed out that collapse is not the only hazard of buildings. Sudden rapid increase in fire is another. The Rockland County, NY, Fire Training Center has developed a great structure and program to demonstrate FLASHOVER. To get a description of the structure and further information, write to Fire Instructor Gerald Knapp, 9 Mackey Road, Garnersville, NY 10923.
Lessons Learned From The Milliken Fire
The January 1995 fire at the giant Milliken & Co. carpet mill in LaGrange, GA, was another costly example of the dangers of metal deck roof fires and another classic illustration of this type of roof deck fire as described in Francis L. Brannigan's book, Building Construction for the Fire Service, third edition. (See "On The Job Georgia," Firehouse, June 1996.)
Milliken is provided property coverage by Industrial Risk Insurers (IRI). The third-quarter 1995 issue of the company's publication, IRI Sentinel, discussed the "Tale of Two Fires," noting that the roof deck fires at a General Motors transmission plant in Livonia, MI, in August 1953 and the Milliken fire resulted from very similar reasons (see "On The Job Georgia").
Once the temperature of a fire impinging on a Class II metal roof deck reaches 800 degrees Fahrenheit for more than about five minutes, the tar melts and vapors from the roof assembly ignite. The fire will then "self-sustain itself" along the bottom of the roof deck, even in a sprinklered building. Buildings of this type are protected by typical "upright" sprinkler heads. These heads are designed to deflect the water downward. In a metal deck roof fire, however, little water hits the bottom of the roof deck, which would cool the metal deck from the bottom. In effect, the fire is running over the top of the sprinkler protection.
A metal deck roof incident will have the fire spreading and burning the flammable vapors generated when the asphalt, used to adhere the board to the metal deck, melts and vaporizes. Because the insulation board and various layers of felt and asphalt (built-up roofing) above the insulation block upward, and since the asphalt vapor is heavier than air, it will drop downward through the overlapped and unsealed seams in the corrugated or wide-rib decking. When it hits the hot environment inside of a fire building, it ignites beneath the roof. The heat of the vapor burning just below the metal decking causes more asphalt to melt, creating more vapor and away the vicious circle and self sustaining fire goes. This metal roof deck fire will continue to burn very hot and with huge volumes of dense black smoke.
Once started, a metal deck, self-sustaining roof deck fire can burn even in a completely empty building. This fire will burn until the fire reaches the ends of the building or until LOTS of water is applied to completely cool the metal deck to stop the self heating scenario associated with what is commonly called a Class II steel deck roof. It is almost like having asphalt in a frying pan.
Many firefighters fail to fully understand the seriousness of these types of roof deck fires and how quickly the self sustaining fire can begin. Of equal and sometime greater importance is how fast this type of fire will weaken the steel "bar joist" and steel beam supports, bringing the roof deck down on unsuspecting firefighters. Asphalt has a flash point of about 400 degrees F and a boiling point of 700 degrees F, per NFPA 325 and Factory Mutual Data Sheet 7-19N.
Dave E. Williams