Polyethylene Wall: “Gasoline Construction” for Houses

BY JAMES TODD SOONG

At 2135 hours on Friday, the tones drop for a house fire in one of the many 100-unit subdivisions built during the 1990s in your response district. From a considerable distance, you can see a column of heavy black smoke rapidly rising from the area of the reported fire. The initial size-up of the structure shows a medium two-story home with heavy fire from side Alpha and exposure concerns on sides Bravo and Delta.

As you call for a second alarm to your location, the resounding thought bouncing around your mind is, “This is an extremely high volume of fire for this neighborhood at this time of night.” Your 360° size-up shows fire is now “forcefully blowing” from all windows on side Charlie and the exposure on this side, approximately 100 feet away, is being damaged by the radiant heat this fire is producing. The family residing in the home greets you on your return to the apparatus and tells you that everyone is out of the house.

Your assistant chief with 40-plus years in the fire service shares your astonishment at the volume of fire and the aggressive fire spread accompanying it. How can this home, one block from a major, heavily traveled thoroughfare, have produced this much fire without an earlier call being made? Moreover, the homes are 12 feet apart. How can the fire have grown so dramatically in this neighborhood?

Although this scenario can play out daily in areas all across our country, the type of fire growth experienced is more typical of fire incidents at an abandoned structure or structures in remote locations of your response area. A small subdivision with homes so close together within three minutes of a fully staffed fire station should not have this type of head start on a Friday night.

Although this rapid fire growth may seem at first to be a one-of-a-kind phenomenon, the construction features behind the rapid fire spread are all too common as the ever-changing world of lightweight construction takes yet another twist.

fire started outside by the front porch and the garage wall
(1) This fire started outside by the front porch and the garage wall. The owner saw smoke go by the window. He evacuated his family and called 911 from two houses down the street. He returned within three minutes of exiting the home to take this photograph. The exterior finish on the house is vinyl siding. [Photos courtesy of the Rock Community (MO) Fire Protection District.]

Polystyrene Wall

In the Midwest, during the early 1990s through the early 2000s, there was a sizeable construction boom of new housing. Contractors building subdivisions of approximately 70 to 250 houses on one-quarter- to one-half-acre lots or smaller used a construction feature that has only recently made itself obvious.

With this construction feature, plywood or oriented strand board (OSB) wall sheathing was replaced with ½-inch polystyrene tongue-and-groove insulation board. To replace the structural contributions of the plywood or OSB, the polystyrene construction was reinforced with 1½-inch metal bracing run diagonally, nailed flush over three 2 × 4 studs (the wall framing). The polystyrene-constructed wall could then be given a final external sheathing, usually polyvinyl siding, along with a brick façade on the front of some homes. The interior wall features are unchanged: 4- to 8-millimeter polyethylene sheeting covering insulation under ½-inch gypsum board (drywall).

The new construction feature could save a builder from 10 to 25 percent over the cost of plywood or OSB. Most new home purchasers had no idea of how flimsy the wall construction was. Likewise, most fire departments were caught flat-footed in the inspection/anticipation of the volatility of this new design.

Structurally, the homes are as solid as plywood- or OSB-sheathed homes. They hold their own against the forces of environmental loads such as wind and gravity. The structure will be well insulated, and adaptations of traditional construction techniques can be implemented to bear the load of a brick or stone façade. From a builder-purchaser perspective, an innovation on a structural component has been put in place to allow a builder to deliver a product in demand by a purchaser. From a firefighter’s perspective, however, we have a radically new problem to consider.

The components of this type of construction are manufactured during the process of refining crude oil-thus, the moniker “Gasoline Construction.” Polystyrene is manufactured 12 steps down the chain from gasoline. Vinyl siding is the most stable of the components used in this construction feature and withstands the most heat of the other hydrocarbon-based products.

Side Charlie neighbors of this gasoline constructed house were on the back deck having a party at the time of the fire
(2) Side Charlie neighbors of this “gasoline” constructed house were on the back deck having a party at the time of the fire. The fire began in the upstairs master bathroom, side Delta (note the small fire glowing below the attic). The migration of carbon dioxide found the attic. Note the side-to-side attic involvement.

MECHANISM/PROGRESSION

As the fire begins, whether from the interior or exterior, the structure begins to absorb and transfer heat. The room’s resistance to flashover is based on factors such as its ability to absorb heat, the available air supply, and the behavior of the products being burned. As the fire becomes hotter or as the room’s ability to absorb fire is taxed, heat begins to spread to adjoining structures and push back into the fire area, intensifying the burning process. As the heat is conducted or convected, the adjoining components are exposed to that heat.

The lightweight construction and low density of polystyrene allow for high air flow into the product and expose more of the product’s surface area to the fire. A result is a more rapid advance of the product’s destruction, which, because of its volatile nature, occurs at lower temperatures. The main by-product, carbon monoxide, is then produced in large quantities in a short time. Depending on the locations of each of these products, the by-products of combustion will collect in potential or actual spaces: attics, cocklofts, porch roof structures, and so on. This transfer creates large amounts of superheated combustibles in areas often removed from the origin of the fire. As the fire progresses or as these super-heated gases find an ignition source, extension can be aggressive and even explosive.

As the fire progresses, fire spread is intensified by the breakdown of these products, which extends throughout the structure through the void spaces and interior openings of the building and gathers in the structure in abundance, unchecked by fire-stopping, as the components are wrapping the building’s fire-stopped components. In essence, a chase (similar to balloon construction) is created and is protected by the exterior covering (siding, stone, brick) and the drywall interior finish.

This fire progression is happening in dramatic fashion. In two cases in the Rock Community Fire District (near St. Louis, Missouri) the fires occurred on weekend nights in subdivisions with moderate to heavy automobile traffic. In one case, a deck party was in progress on exposure C at the time the fire began. In each case, the homeowners were alerted to the fire by signs of burning (fire noise, smell of smoke) and the smoke detectors. Calls were received by 911 within one minute of the occupant notification; the first-due units arrived within five and seven minutes. In each case, the first-due officers were met by a heavy fire load with aggressive threats to the exposure. Both scenarios overwhelmed the first-due officers in terms of fire attack and had them marveling at the amount of fire and the aggression of fire spread and the rapid fire growth.

A complete 360° size-up of the structure revealed not only heavy fire involvement but also the loud roar of a fire being pushed by a pressurized vapor, which is exactly what was going on. One of the structure fires had heavy fire pushing from windows and was accompanied by the noise of a force-fed fire, a sound similar to that of a jet airplane engine.

IDENTIFYING HOMES WITH “GASOLINE CONSTRUCTION”

In looking for these buildings in your response area, refine your search to subdivisions built in the 1990s and early 2000s. Polystyrene foam board wall sheathing was used purely as an economic decision. When its price became cheaper than 7⁄16-inch OSB, developers who could purchase it in bulk used it. That’s the reason it is prevalent in subdivisions of 150 to 200 homes. The developer could realize a 20 percent savings, and there was little chance the home buyer would be aware of its presence.

During construction of new subdivisions, pay attention to what is on the wall prior to the finish layer (polyvinyl-chloride siding, brick, or stone façade), and identify the materials staged on the job site. Large stacks of blue, pink, or light green 1⁄2-inch insulation board should catch your eye! After the home is shelled (exterior construction completed), a walk-through prior to erection of the wall insulation should show the exterior wall product from the inside. In fact, on a vinyl-sided home with polystyrene sheathing, daylight will actually filter through the wall.

MOVING FORWARD

The modern day fire service will continually be interested and involved in the products and processes that go into the construction of the buildings we are to protect. The modern construction industry will continually be interested in building a product with innovative processes and components that afford them the largest profit margin. This is the essence of American capitalism. Just as with today’s struggle to bring sprinklers into our homes, the struggle will be to educate builders, developers, code officials, municipal planners, and the general public.

For us, as the last stand between owners of these homes and the destructive nature of fire, the message is timeless: Know your buildings; know your subdivisions! As you discover homes or subdivisions with this construction feature (or any type of variance on lightweight construction), spend adequate time training and discussing strategy and tactics with your company and department and within your circle of influence as a fire professional. Realize that the time to flashover has been tremendously reduced. As a first-due apparatus, your arrival can coincide within seconds to a few minutes of flashover. Adjust your tactics accordingly. Consider rapid vent-enter-isolate-search for rooms with evidence of occupant survivability.

Look at these homes as much as possible. On the plus side, their lightweight construction feature also allows for easier egress should a firefighter or crew become lost or trapped. A home with vinyl siding, polystyrene wall sheathing, and drywall can literally be breached with a utility knife. This construction type and these materials should never be able to contain a thinking firefighter with the proper tool in his hand.

Consider and implement a preplan for these subdivisions and homes. Implement language into your initial size-up report that provides a cue for listening/incoming units: “Engine 2 on scene, medium two-story residence, lightweight construction, heavy fire/smoke showing sides Alpha and Bravo. Engine 2 with Main Street command, strike a second alarm.”

Ultimately, attempt to reach out to the builders of these homes. If your district or department provides fire inspections, educate the developers and builders constructing these homes. Consider an incentive program such as reduction of permit fees or implementing a rating system for extra safety features included in the home-“five star” homes built with residential sprinklers, for example. Be diligent in these existing neighborhoods as well. Conduct frequent training sessions and district familiarization drills to remind your crews about the dangers and fire spread potential of this type of construction, and conduct programs for occupants about the importance of smoke detectors and other fire safety programs.

Keep an eye on the prices in your local building supply store. Polystyrene is a by-product of crude oil. As the cost of a barrel of oil rises or drops, so will the price of this insulation board. As the price of 1⁄2-inch polystyrene tongue and groove drops below the cost of 7⁄16-inch or comparable OSB, realize that the entrepreneurial home builder will be considering using this product. Again and above all, begin each fire attack in these residential neighborhoods with the highest level of concern that you are fighting a home built with “gasoline construction.” Make the conditions of the fire attack from your side of the fight. Make it safe for you and your crews.

Material Safety Data Sheet

Following is some information contained in the material safety data sheet of a manufacturer of polyethylene sheeting for construction.

• Composition/Information on Ingredients: Component CAS Registry Number Percent by Weight, Polyethylene 9002-88-4 99 – 100, Calcium Carbonate 1317-65-3 0 – 1.

• Hazards: Primary routes of entry are skin contact and inhalation of dust. Inhalation is a low health risk because any potentially hazardous components are encapsulated. Inhalation of dust is a possibility in a regrind area. If adequate ventilation is not available in grinding areas, then respiratory protection is recommended per Occupational Safety and Health Administration (OSHA) guidelines. Where there is hazardous or nuisance dust, either a mandatory or voluntary OSHA defined program of respiratory protection is recommended. The permissible exposure limit for nuisance dust is 5.0 mg/m3.

• Firefighting Measures: (National Fire Protection Association: Health = 0 Fire = 1 Reactivity = 0 Others = 0) The flash point of this material is over 600°F. If a fire should occur, carbon monoxide (CO) and irritating smoke may by produced. Wear National Institute for Occupational Safety and Health-approved self-contained breathing apparatus when fighting fires in enclosed areas. Fight with water, carbon dioxide, or dry chemicals. Use flooding quantities of water until well after the fire is out.

• Handling and Storage: This product is normally shipped on pallets in boxes. The pallets should not be stored more than three layers above ground level. The pallets, boxes, and plastic film will burn in the presence of open flame. Do not weld or use open flame (welding) where product is stored. This is especially true in the case of the storage of powder. Always ensure that proper firefighting prevention equipment is readily available.

• Physical and Chemical Properties: This product is film sheeting with a volatile organic compound content of less than 5 parts per million. Density will vary depending on color and components from 0.85 to 1.5 nominally. The product can sink or float in water depending on the properties. The product is not soluble in water and is odorless at ambient temperature. A characteristic plastic smell will be obvious when the product is heated.

• Stability and Reactivity: This product is stable and non-reactive. Hazardous decomposition of products can occur if overheated or ignited.

• Toxicological Information: No known or suspected carcinogens per the National Toxicology Program, the International Agency for Cancer Research, or California Proposition 65 are in this product. If any of the chemicals were present in reportable weights, they would be listed in Section I of this document.

• Transportation. The product [manufactured by this manufacturer] is not a regulated substance under the Department of Transportation regulations. All hazardous components of this material (if any) are encapsulated and therefore provide no transportation threat.

• ISO 9001-2008 certified.

• SARA 313 Information: This product contains no chemical subject to SARA Title III section 313 Supplier Notification Requirements. [The company] states this to the best of its understanding. SARA Hazard Category: This product has been reviewed in accordance with Environmental Protection Agency Hazard Categories (SARA Title III) and is considered, under applicable conditions, to meet the following categories: Not to have met any hazard category.

• Toxic Substances Control Act (TSCA): [The company] has put all necessary ingredients on the TSCA Inventory.

• State Right-to-Know: This product is not known to contain any substances subject to disclosure requirements of New Jersey, Pennsylvania, and California.

• OSHA Hazard Communication Standard: [This company’s] Manufactured Construction Film is not a “Hazardous Chemical” as defined by the OSHA Hazard Communication Standard, 29 CFR 1910.1200.

JAMES TODD SOONG, a member of the fire service for more than 20 years, is a captain/paramedic for the Rock Community (MO) Fire Protection District. His class “Gasoline Construction” was presented at FDIC 2011 and throughout Missouri. He is also an International Association of Arson Investigators certified fire investigator and a certified instructor for NEFCO Fire Investigations.

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