Photo from Loudoun County Department of Fire, Rescue & Emergency Management
On June 12 STATter 911 ran an item about a truck fire a day earlier in Loudoun County, Virginia. Chief Fire Marshal Keith Brower made the case this fire clearly showed the problems when vinyl siding is exposed to fire.
Deputy Chief Brower pointed out how vinyl siding on the home next door melted from the radiant heat. The siding on the home where the truck was parked, about three times closer to the flames, was relatively unscathed. The Hardy board on that home only showed slight discoloration from the radiant heat.
Chief Brower and many others in the fire service have long cautioned the public and reporters about their concerns vinyl siding contributes to fire spread.
Since the story ran on TV and here on STATter 911, we have been in touch with representatives of the Vinyl Siding Institute (VSI) in Washington, DC (they were unavailable on the day of the story due to a prior commitment with Habitat for Humanity).
We offered VSI the opportunity to address some of these issues involving vinyl siding under fire conditions. VSI’s code and regulatory director Matt Dobson and senior technical director David S. Johnston responded to the offer with the following guest column. In it, they also address three questions posed by STATter 911.
As always we encourage opposing viewpoints.
Vinyl Siding: A Fire Safe Cladding
By: Matt Dobson and David S. Johnston
There are many reasons why residential fires start and spread, but the type of cladding materials on the outside of a house is rarely one of them. In fact, in 2007, the National Fire Protection Association (NFPA) reported that fewer than three percent of all fires go beyond the structure of origin and fewer than two percent of all home fires’ source of origin is related to the exterior wall surface. Only four percent of all residential fires start on the outside of the structure, but do not necessarily originate with the exterior cladding. The report does not cite any exterior wall coverings (including vinyl siding, brick and stucco) as the cause of residential fires.
In the recent – and very unfortunate – Loudoun County truck fire occurrence, the media paid much attention to the vinyl siding that melted on a home nearby, deflecting focus from the real source of ignition – a commercial truck with a generator in the back which caught fire that spread to the rest of the vehicle.
The fact is: Safe homes use fire safe cladding, which includes vinyl siding.
In an e-mail, Mr. Statter asked three questions of the Vinyl Siding Institute, Inc. (VSI). These questions, and our responses, are below.
Statter: I have seen countless fires involving communities with vinyl siding and see damage from radiant heat a great distance from the fire source. This generally does not happen with other types of siding. How is this better?
Dobson and Johnston: Vinyl siding can soften, sag or melt when exposed to radiant energy from a fire, but is not likely to ignite when merely exposed to radiant energy. Vinyl siding typically passes the radiant exposure test in NFPA 268 without exhibiting sustained flaming, and is thus eligible for use even at the minimum fire separation distance permitted by the code (see section 1406 of the International Building Code). Ignition of vinyl siding usually needs to be piloted – it has to be exposed directly to flames before it will ignite. Unless an external fire actually approaches the side of house, the vinyl siding is not likely to ignite. Interestingly, vinyl siding is allowed for use with fire resistive assemblies. In fact, several fire rated assemblies actually specify either vinyl siding or fiber cement.
Thus, while melted siding looks bad, it does not represent an actual or likely hazard. Many building materials, particularly those made of plastics, wood, or any painted material, will be damaged when exposed to the heat from a fire, and vinyl siding is not unique in that respect. The siding will need to be replaced (which will be less expensive than for other damaged siding materials), but the melting of siding does not represent a safety issue.
Also, when looking at residential fire issues involving life safety and property damage, the vast majority occur on interior of structures.
Statter: Fire officials, including Chief Brower, tell us that when exposed to heat, vinyl siding breaks down to an oil based product that helps spread the fire. Is that accurate?
Dobson and Johnston: Vinyl siding is composed of approximately 50 percent chlorine (typically derived from common salt) and hydrocarbons derived from ethylene, typically sourced from natural gas. Vinyl siding is itself a petroleum-based product (though not “oil-based”), although it contains less petroleum than most other plastics. It is the presence of chlorine that imparts significant fire retardant characteristics to vinyl siding. When vinyl siding is heated it gives off chlorine compounds which, much like gaseous, chlorine-based fire-extinguishing agents, inhibit the chemical reactions needed to sustain combustion. This is the reason that it is extremely difficult to ignite vinyl siding by radiant energy alone. If siding is placed into an active fire, the hydrocarbons will burn, but combustion will continue to be inhibited by the presence of chlorine compounds. In a building fire, other materials, especially wood materials such as OSB or plywood sheathing under the siding, burn much more aggressively, with a higher rate of heat release, than vinyl. If the heat given off by other materials is removed, combustion of the vinyl by itself will die back rapidly, and it may fully self-extinguish.
In a real-world building fire, the breakdown and combustion of carbon-based materials is chaotic, and many different types of reactions are taking place simultaneously. Unlike many other materials, vinyl siding has a built-in advantage of containing a combustion inhibitor, chlorine, which will be present during the most active stages of combustion. After the chlorine and hydrogen components of vinyl have been exhausted, the remainder is char, primarily carbon, which will burn primarily with glowing, rather than flaming combustion.
Statter: Fire officials have claimed throughout the U.S. and Canada that vinyl siding has been one of the contributing elements in fire spread during some pretty major conflagrations in a number of communities. How do you answer that?
Dobson and Johnston: Fire officials have observed walls of standard combustible construction burning and have mistakenly attributed rapid combustion to the vinyl cladding. They are, in fact, observing the fire behavior of common combustible sheathings, with a relatively small fuel contribution from the vinyl. As described previously, vinyl siding by itself will not burn aggressively and will tend to die back. If kept in the presence of burning sheathing it will burn, but will be inhibited by the presence of chlorine gases. This behavior has been demonstrated experimentally and in real world applications. When vinyl siding is applied to a wall sheathed with gypsum wall boa
rd and ignited by an external gas flame, it will burn as long as the external flame is applied, but the fire does not tend to climb up the wall aggressively. If the external heat source is removed, combustion of the siding will die back and may self-extinguish. Thus without the large amount of heat given off by burning wood sheathing, vinyl siding does not burn aggressively nor contribute significantly to fire spread.
Canadian building and fire officials in Alberta have investigated large fires involving standard residential construction and taken steps to firm up certain requirements in their codes. Significantly, they decided not to restrict the use of vinyl siding, even at very close fire separation distances. However, this is a comprehensive issue that involves consideration of other factors like ignition sources, properly supervised construction sites, properly maintained fire service infrastructure and how structures are built.
A claim stating that vinyl siding contributes to the aggressive spread of a fire is a misperception, and, in our experience, we have not found this to be widespread among fire officials throughout the U.S. and Canada. We have worked directly with the NFPA, International Code Council (ICC) and Safety Codes Council. Fire officials from these organizations understand vinyl siding’s behavioral characteristics in a fire and find it to be safely regulated through the building and fire codes.
For more information on vinyl siding’s fire safety characteristics, please visit the Vinyl Siding Institute’s website at http://www.vinylsiding.org/.
Matt Dobson is the code and regulatory director for the Vinyl Siding Institute, Inc. (VSI) and a long standing member of the National Fire Protection Association (NFPA). Through his association with the NFPA, he served as a technical committee member for the Uniform Fire Code (NFPA 1) and the Life Safety Code (NFPA 101). These documents now serve as resources to fire officials across the country and are critical to helping them maintain and improve fire safety in buildings.
David S. Johnston is the senior technical director for the Vinyl Siding Institute, Inc. (VSI) and his experience includes extensive building code and product standards development work. He is the former chair of the National Fire Protection Association (NFPA) Technical Committee on Chimneys and Heat-producing Appliances. Additionally, he is a former member of the International Code Council (ICC) International Fuel Gas Code Committee. Johnston is a current committee member for development of the ASTM E5 (Fire Testing), E6 (Performance of Buildings) and D20 (Plastics).
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