NEW CONSTRUCTION, OLD PROBLEMS

BY ALLEN B. CLARK, JR.


(1) Foam building modules arrive on-site. (Photos by author.)

After 20-some years of studying and teach-ing how construction affects fire spread, structural integrity, and firefighter safety, I thought I had seen just about every type of construction material. Then, recently, right in my neighborhood, up pops something new—polystyrene foam building modules. I actually discovered the material when massive amounts were delivered to the construction site (see Photo 1).


(2) The split-level house before doors, windows, and roof are installed. Note the trusses. The white is the polystyrene foam-type construction blocks that will be filled with concrete.

My primary concern was the flammability of the polystyrene-type materials, especially when used in such quantity. I followed my first instinct, which was to call Frank Brannigan and ask about it. He was aware of the material but did not have any first-hand knowledge about it. We discussed it, and he advised me to go with my analysis.

THE BUILDING


The building in which it was to be used was a single-family split-level house. Despite outward appearances, there are four levels; the first is below ground (see figures 1 and 2). The sleeping area is in the elevated portion; the area immediately below is a den/family room (see photo 2). The area to the right contains the living room, kitchen, dining room, and laundry room. The latter two are in an extension to the rear that isn’t apparent from a frontal view. Below these rooms is a basement. Eventually, the house is to be covered with brick veneer and will resemble the typical split-level of wood/veneer construction.

THE CONSTRUCTION


(3) A center panel. Note the tube channels and plastic webbing holding the foam sheets.

The polystyrene foam webs are formed with plastic links that create oval vertical and horizontal channels approximately six inches deep by eight inches wide (see photo 3). Open plastic webbing allows free flow between columns for fill. Blocks or panels are used to form the bearing walls. Offsets are braced in place, and door and window frames are formed and framed (see photo 4).


(4) As the blocks are assembled, they are held in place by supports. Window and door openings are in place and reinforced. Notice the interior joist hangers in place for the elevated floor.

Steel rebar is placed in the vertical channels and tied together with rebar through the horizontal channels (see photo 5). The joist hangers are placed in slots in the foam sheet, and a piece of rebar is inserted in a hole in the hanger (see photo 6). After the foam structure is formed, reinforced in place, and heavily supported, concrete is injected into the channels. It can be put in by pressure, forcing it up tubes, or by bucket from the top, to allow it to fill all voids and form a monolithic grid. This system forms a strong, highly insulated building shell.

PHYSICAL PROPERTIES: EXTERIOR WALLS


(5) Rebar is placed in the tube channels and tied in to form an internal structural support web.

My original concern was with flammability of the foam building component. I obtained permission and help from the builders to conduct a crude test (see photo 7). A lighter was held to the sample for approximately 30 seconds. No flaming resulted; however, it did melt (see photo 8). Later while observing construction, I saw a worker use a propane torch to melt one of the slots for a joist hanger. This is no guarantee that some burning would not take place during a fire involving contents and/or the interior substructure. No attempt was made to ascertain the toxicity of gases released by the melting materials.


(6) A joist hanger is put in place. The hole (arrow) is for a cross-connected bar to support the hanger.

The core of the exterior walls is formed by a grid of concrete. Structural bearing wall collapse should still be a consideration. Although it is noncombustible, it is not required to meet any published fire resistance standard.

PHYSICAL PROPERTIES: INTERIOR


(7) A crude flammability test is conducted by holding a lighter to a small sample of the foam.

Floors are constructed with composite board (plywood/particle- board) on joists supported by wood studs (see photo 9). To cover a span of approximately 24 feet, fabricated wooden I-beams are used (see photo 10). These beams are notorious for sudden failure with even less warning than ordinary trusses. It is usually instantaneous and catastrophic. The thin web of the beam is laminated wood and subject to poke-throughs for electrical, plumbing, and heating connections. Once the web is compromised, the joist will have the same strength as a 2 2 4 laid flat. To make matters worse, the 2 2 4 flanges are usually shorter spans spliced to form the length necessary for such a long span.


(8) The foam melts but does not ignite or sustain flame. In fact, some of the joist hangers were put in place by melting a slot for them with a propane torch.

As seen in photo 2, a considerable number of trusses are used in the roof system. This creates a virtual lumberyard in the attic space. Both the roof and interior raised floor can be expected to fail early once attacked by fire. The irrevocable law of gravity will then make the outcome inevitable.

FIREFIGHTING FACTORS


(9) Different interior levels are formed by what appears to be conventional wood framing-joists on studs.

Following are some observations and recommendations for firefighting pertaining to this new material:


(10) A closer look reveals the wooden I-beams used as joists to provide longer span capacity.

  • Because of the overlap of foam, this building will be well-sealed. This can have a negative impact should there be a carbon monoxide leak or a fire in the building. It will act as an oven to contain heat.
  • Prior to the addition of the veneer, it may be possible to use a piercing nozzle for fires with serious involvement to minimize exposure to firefighters.
  • Early ventilation will be a priority.

    ALLEN B. CLARK, JR., has been a member of the Bell Township (PA) Fire Department for 24 years and is currently assistant chief and safety officer. He is a senior field instructor for the Pennsylvania Fire Academy, a contract instructor for the National Fire Academy, an adjunct faculty member at Westmoreland and Allegheny County Community Colleges, and a consultant on issues pertaining to fire safety and related matters. He is a nationally certified Firefighter III, Fire Instructor III, and Fire Officer I and has an associate’s degree in fire science, a bachelor’s degree in fire administration, and a master’s degree in safety science.

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