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Tuesday, 17 June 2014

Fire Resistance

 The Construction Specifier
Solutions for the Construction Industry - October 2007


Fire resistance and combustibility
When used with various construction types and occupancies, vinyl siding must comply with sections of the International Building Code (IBC).

High ignition temperature
Low ignitability is the first line of defense in a fire. All organic materials ignite, but the higher the temperature a material has to reach before that happens, the safer it is. Polyvinyl chloride (PVC) does not ignite until the temperature hits approximately 388 C (730 F) even in the presence of flame, and will not self-ignite until about 454 C (850 F). These ignition temperatures are significantly higher than those of typical framing lumber, which has a flash ignition temperature of 260 C (500 F) and self-ignites at 410 C (770 F).

High limiting oxygen index
According to research by the Vinyl Institute, using ASTM International D 2863, Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-like Combustion of Plastics (oxygen Index), to determine rigid PVC's high limiting oxygen index (LOI) shows the material takes unusually high amounts of oxygen to burn and remain burning. (1) It will not independently sustain combustion in air with a normal concentration of oxygen (about 21 percent).

Low surface flammability
Test results using ASTM E 162, Standard Test Method for Surface Flammability of Materials Using a Radiant Heat Energy Source, shows PVC as one of the materials with the lowest flame-spread rating, meaning it will not readily spread fire on its own. Vinyl products do not quickly ignite and are inherently flame-retardant due to their chlorine base. Regarding combustible claddings, vinyl can be seen as superior to other products, such as untreated wood, which typically has double the flame-spread rating.
Most vinyl products will not continue to burn once a flame or heat source is removed and have been proven to be no more hazardous than those products by many other common materials, both natural and synthetic. (2)

Toxicity
At least to some extent, fire hazards are also associated with the toxicity of the smoke itself. The most important toxic product in any fire is carbon monoxide (CO), which is produced by all organic materials when they burn.
The Society of the Plastics Industry (SPI) funded a comprehensive study of fire (and non-fire) fatalities associated with carbon monoxide. Published in 1992, it examined approximately 5000 deaths and found the toxicity of fire atmospheres is determined almost exclusively by carbon monoxide. NIST has since developed a new definitive smoke toxicity test that has found most fatalities occur in fires that become very large (i.e. go to flashover). The CO concentrations in these events are virtually unaffected by the materials burning.
Vinyl materials are well within the normal range of toxicity when compared to other combustibles, with lethal concentration (i.e. LC50) values of more than 8 mg/L. (3) The major combustion products given off by PVC are the same as those produced by wood or most other common materials. The one product given off by PVC not emitted by natural materials is hydrogen Chloride (HCI). Extensive studies have shown the mechanisms of action of CO and HCI are totally different, but their lethal doses are very similar. Unlike CO, HCI has a very pungent odor, which is detectable at a level of less than 1 ppm, while CO is odorless and narcotic. Therefore, HCI can signal people to escape, while CO will narcotize them. (4)

Read the PDF - Construction Specifer, October, 2007


(1) See "Fire and Polyvinyl Chloride,"a 1996 report by the Vinyl Institute. (2) See (5). (3) LC50 is the concentration of a material in the air that causes the death of 50 percent of a group of test animals. The material is inhailed over a set period, usually one or four hours. (The LC50 helps determine a material's short-term poisioning potential). (4) See (5).