Better Standards Rise from Livonia’s Ashes
To understand better what happened in that fire, a test building was constructed, replicating the Livonia structure. The building, known as the “White House” (from where the “White House Test” is derived) was 100 feet long and utilized purlins, decking, and other parts that exactly matched the Livonia building. An under-deck fire was ignited at one end of the building, and the progression of the fire closely observed. The fire moved from end to end in 10 minutes. A new deck providing more limited fuel burned end to end in 12 minutes, and a roofing and deck system with no vapor retarder and only narrow ribbons of asphalt used to adhere the thermal insulation to the deck burned in 13 minutes.
The combustibility of all of these assemblies was considered unacceptable. When mechanical fasteners were used to attach the thermal insulation directly to the metal deck, the fire only spread 60 feet down the building during the 30-minute test burn. This became, and still represents, an acceptable level of fire risk. Had the Livonia fire burned at that slower rate, the building’s fire brigade could have controlled the fire and saved the building.
The next step was to develop a laboratory scale fire test that replicated the “White House” and Livonia constructions.
FM Global uses a furnace (calorimeter) that measures heat released by the test specimen, with no more than 400 BTU per minute released during the steepest three minutes of the temperature curve. Successful constructions over steel roof decks are designated by FM Global as Class 1.
To establish burning on the underside of a test deck. UL uses a 25-foot-long test chamber called a Steiner tunnel and measures the progression of flames on the under-side of the roof deck. UL’s allowed criterion is that flames shall progress no more than 10 feet down the tunnel in 10 minutes and 14 feet during the entire 30-minute test. Successful test constructions are found under the classification of insulated metal decks.
Class A Doesn’t Mean Grade A
These tests pertain only to fire performance. In many cases, a thinner roof system will have better fire performance because it contains less fuel to feed a fire. However, in terms of durability, a thicker membrane (i.e. more plies or a thicker single ply membrane) may well be a better, more durable roof.
Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems and continues to participate in seminars for the University of Wisconsin and RCI Inc., the Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, the William C. Correll award from RCI, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.
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