Fenestration Review

Articles Dealer’s Corner
Editorial – Burning questions


October 30, 2013
By Patrick Flannery


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A window and door fabricator commented to me recently that he sometimes runs into an objection from architects regarding the combustibility of his PVC window profiles. They say they cannot use vinyl on commercial projects because the building code requires “self-extinguishing” materials, and PVC is considered combustible. This is partly, but not entirely, true. And I’m not sure it should be true at all.

A window and door fabricator commented to me recently that he sometimes runs into an objection from architects regarding the combustibility of his PVC window profiles. They say they cannot use vinyl on commercial projects because the building code requires “self-extinguishing” materials, and PVC is considered combustible. This is partly, but not entirely, true. And I’m not sure it should be true at all.

The National Building Code of Canada calls for buildings over three stories or with very large interior areas to use non-combustible materials in their construction. However, there is a specific exemption for window sashes and frames (Section 3.1.5.4 (5)) allowing so-called combustible sashes to be used even in a non-combustible building, provided the windows are sufficiently separated by non-combustible wall materials. So unless the building design calls for large, contiguous windows on the upper stories, it may be possible to use PVC profiles under the present codes.

But a more interesting question might be whether PVC should be considered a combustible material at all. Certainly it is according to the present definition, which calls any material combustible according to its performance under the CAN/ULC-S135 testing protocol. S135 measures the amount of heat given off by a material at high temperatures, and also the amount of smoke it produces. According to Stanis Yu of Underwriters Laboratories of Canada, PVC would always fail this test. But is this standard the right one?

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Way back in 1985, Jim Mehaffey, then a researcher with the National Research Council, wrote an article called “Combustibility of Building Materials.” In it, he explained that the need for non-combustible construction was driven by the need to keep fire from spreading quickly. It does not matter so much whether a material will ignite, he said, but whether it will continue to burn after ignition. I don’t pretend to be an expert on the S135 test, but I’m not sure how an instantaneous measure of how much heat a substance is releasing adds up to an evaluation of whether it is burning or not. It seems to me a substance would have to continue to give off a certain level of heat over time before it would pose a danger of spreading fire.

Add to that the results of a study by M.M. Hirschier posted on pvc.org showing that PVC plastic requires twice the oxygen concentration of normal air in order to keep burning after ignition. So, at regular oxygen concentrations (like those present around your average building fire) PVC will not continue to burn unless a flame is continuously applied to it. Sounds pretty self-extinguishing to me. Maybe it is time to re-evaluate whether PVC window profiles do qualify as a combustible material in a way that actually poses an increased fire hazard.

But enough of the high-forehead stuff. I want to direct your attention to our masthead on the left side of the table of contents, and to a very important new line that appears there: Endorsed by Fenestration Canada. Fenestration Review is honoured to have received this important recognition from Canada’s window and door association, and we are looking forward to working closely with all the good folks there to promote and improve this industry. Thank you to Fenestration Canada and thanks to you, our readers, for your enthusiastic reaction to this magazine.