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... Continuing last week's Polywater Laboratory email narrative on FST Foam Duct Sealant: Q: Are there dangerous by-products when FST is exposed to fire? A: Please see the attached FST Combustion Statement. Q: How dangerous is the gaseous concentration for 48 ducts in a confined space? A: To reply accurately we need the exact dimensions of the enclosed space and information on ventilation (rates / debit volumes). Are we assuming that the full plugs are burning or only a portion of them, such as when they'd be cut through with a torch? Should we assume a worst-case scenario where the entire duct bank is ablaze, even if this is highly unlikely? Please clarify. Q: Assume a 10' x 10' x 10' chamber with 24 plugged ducts in each wall (4) and the chamber is on fire. There is a 3' lid. No extra ventilation. A: First, let's start with the make-up of the gases that are generated by burning 2-part FST. From the SDS's for the unmixed and thus uncured A and B sides, we see the following list of decomposition products during a fire: carbon monoxide, hydrogen cyanide, nitrogen oxides, aromatic isocyanates, which are gases/vapors from the isocyanate side ... and carbon monoxide, carbon dioxide, phosphorus oxides, silicon dioxide, hydrogen chloride gas from the polyol side. Of course, in use, there is no A or B side in FST, only reacted foam. Therefore, all of these materials are potentially released during the burning of FST, with carbon monoxide and carbon dioxide making up the vast majority based on the molecular composition of the materials. Exact breakdown of which carbon compounds or which nitrogen compounds will be released will depend on the conditions of the fire, such as temperature and the amount of oxygen present. Such determination of exact compounds is beyond our ability to project. Second, we can look at the hazardous nature of the gases released. Rather than consider each gas individually, I've attached an industry paper entitled Polyurethane Products in Fires: Acute Toxicity of Smoke and Fire Gases. The paper summarizes the results of a number of studies performed on the gases generated by burning polyurethanes. The major conclusion is that the greatest hazard in burning polyurethanes comes from generating carbon monoxide, the same as burning natural materials. Third, we consider the amount of FST that is actually burned in our theoretical fire. By the nature of the application of the FST, it is unlikely to burn. FST is deposited into conduits in the walls of the chamber, and is, in fact, recessed two inches behind a layer of the fire retardant damming foam used to install the product. We know from laboratory tests that an extended burn from an outside flame source is needed to breach this foam and even reach the FST. Keep in mind that once the FST is reached by the outside flame source, FST is itself fire retardant, carrying a UL 94 HBF rating. FST will not propagate or support combustion. Therefore, we are dependent upon the fuel and oxygen within our sealed 10' by 10' by 10' room to provide fire to burn along the conduits. I can't predict the amount of FST that will burn under our theoretical conditions, but I can predict that it will be a small amount compared to the fuel to be consumed by the fire in the room. There are several methods for testing and rating the fire properties of sealant products. As I mentioned, FST carries an HBF rating under "UL 94 - Tests for Flammability of Plastic Parts in Devices and Appliances." It was determined, with the help of UL, that this was the proper section under which to test the product. Other products, which are intended to be applied directly to cement board and other wall board, are often tested under "UL 723 - Test for Surface Burning Characteristics of Building Materials." The results of this testing is expressed in terms of flame spread and smoke generation numbers which are in comparison to the burning of red oak. It was determined that since FST is used to block conduits and is not subject to surface burning, UL 723 would not be an appropriate section under which to test our product. |
