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Foam As A Fire Barrier

by David B. South

Urethane foam is an excellent fire barrier when used on the exterior of a building. There are numerous examples of urethane foam roofs saving a building from fire. Burning brands, that can include anything from hot embers to large pieces of burning wood, can lay on a urethane roof for a considerable time before burning through. The urethane insulated roof will simply char. If there is no external heat source, the fire will go out. Urethane requires a lot of heat to keep burning. Where the heat can radiate to the atmosphere, the urethane makes a superior fire barrier.

Back in the days before we worried about heat sinks, thermal barriers and the like, we insulated a common wall in a mattress factory in Twin Falls, Idaho. We sprayed one inch of urethane foam on the metal wall to protect the office from losing heat into the furniture storage area. One night, the mattress storage area caught fire. That fire burned for a very long time.
The Fire Marshall told me that the fire was against the building's common wall for better than an hour before they could cool it. He was amazed that the heat did not come through that common wall.

It didn't because the urethane insulation sprayed on the wall reflected the fire's heat back into the storage area, rather than allowing the heat to come through. The Fire Marshall declared that he knew of no other material, besides concrete, that could hold back fire for the time they needed to extinguish that fire.

Since then, I find the best fire doors are metal on both sides of a urethane foam core. The metal takes care of surface combustion, and the foam insulation prevents the temperature from rising to the point of combustion on the non-burning side of the door.
Then too, urethane foam is a thermoset; that means it cannot be heated and changed back into its original liquid form. When urethane burns, it does not liquefy and run -- as other plastics, including expanded polystyrene or Styrofoam -- do. Urethane either burns very hot, as would an exposed foam building lining, or it doesn't burn well at all. There is no danger of urethane foam smoldering.

The real fire danger from urethane comes from its insulation value, since foam increases the temperatures within the fire areas. But any fire barrier, such as sheet rock, will prevent the urethane from burning by soaking up the heat.

Urethane foam is not much of a fire hazard while being sprayed. In other words, nothing out-gases from it that is highly combustible. Sometimes, various solvents used to clean the gun can be combustible, but the urethane itself is virtually non-combustible.
Once, we were spraying a liner inside the back of a truck in our shop. Admittedly, the shop was full of stuff. There was a pile of plastic sheeting, previously used as masking, in a heap on the floor. A welder working nearby somehow got the plastic pile burning. A co-worker saw the fire and sprayed it out with a foam gun, faster than he could have with a fire-extinguisher. He sprayed right over the flames, encapsulated them and almost instantly extinguished the fire.

Urethane foam components, by themselves, are not a fire hazard and can be shipped without fire hazard labels.

But burning Isocyanate (as a separate chemical) gives off very toxic fumes. Great care should be taken not to breathe these toxic fumes. The chemical by itself will not support combustion. However, if you are disposing of empty Isocyanate drums by removing their tops, do not cut out the top with a cutting torch in a confined area. In fact, it's best if you don't cut out the top with a cutting torch at all. Can-opener top removers for barrels work far better than torches.

If you are using torches, be sure you do not breathe smoke generated by the burning of the Isocyanate. It will make you sick. This smoke is a first cousin to Phosgene gas, that was used on troops in World War I in Europe.

A good caution to remember is never burn organics. Even wood smoke can kill you. It's far better to dispose of chemicals as recommended by their manufacturers than to release chemicals into our environment.

During the mid-1970s, we sprayed more than a million pounds of foam per year. So, I sought information on fires involving urethane foam. I learned that fire information can be severely distorted once the story is told a few times. I found a lightening rod salesman telling people that lightening caused most foam fires and an electrician saying it was wiring.

The fact is most of the fires were caused by large amounts of heat, quick heat -- something like using a cutting torch or a truck on fire. Several fires were caused by vehicles catching fire within buildings.

Nevertheless, nothing yet made will insulate a building as well as urethane foam. But when used on the interior of a building, the foam must be covered with a thermal barrier.

It is absolutely vital that fire be prevented within a Monolithic Dome during its construction. In that short period when a dome is totally lined with urethane, but before the concrete is in place, a fire would be devastating. So caution must be exercised.

Using urethane foam on a Monolithic Dome is ideal. Notice, I said on the dome. Remember, we spray foam on the underside of the Airform, but the foam winds up on the upper side of the concrete. The foam, therefore, is totally protected from interior fire by the concrete shell. And, on the outside of the dome, the foam will not burn anyway and provides a substantial fire barrier.

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