Polystyrene tests reveal need for added fire protection

Polystyrene tests reveal need for added fire protection

Testing by Factory Mutual Research Corporation (FMRC) has revealed that standard, dry-pipe automatic sprinkler systems cannot adequately protect an area insulated with expanded polystyrene (EPS) core panels and must be retrofitted with additional sprinklers or have thermal barriers such as gypsum board applied. The recommendation for additional sprinklers will be incorporated in the revised Factory Mutual Property Loss Prevention Data Sheet 1-57, Rigid Plastic Building Materials. No other revisions were needed in the data sheet. FMRC testing has also shown that the lack of an FMRC-approved thermal barrier, not the polystyrene itself, is the real issue as far as fire safety is concerned.

The foam insulating material polystyrene is used widely in warehouse walls and ceilings in North America, Europe, and Asia. According to FMRC, polystyrene melts like candle wax in a fire, potentially destroying the room it insulates; is twice as combustible (heat of combustion) as wood and 112 times as combustible as urethane; and melts at temperatures lower than 4007F (2047C), forming a flammable liquid with a flash point of about 8007F (4277C). Combustible vapors, forming at about 4507F (2327C), can spread flames rapidly. In addition, polystyrene “emits dense black smoke containing oily, sooty particulates.” A relatively small fire in a food warehouse, a freezer, or electronic equipment can contaminate the entire area. Automatic sprinklers might not confine the fire.

Panel Testing

In 1997, Phil Smith, FMRC senior engineer and project coordinator, conducted a series of 25-foot full-scale Corner Tests (Standard 4880)1 on steel-faced insulated sandwich panels made with EPS cores consisting of two sheets of steel with EPS sandwiched in the middle. The core`s thickness can range from four to 10 inches–and may be even thicker, depending on how it is used. The thickness of the polystyrene in a temperature-controlled environment–such as a large warehousing refrigeration room or freezer–might be more than twice the thickness of that used in an ordinary storage room, for example.

The 25-foot Corner Test evaluates fire spread on various wall and ceiling assemblies measuring 50 feet 2 38 feet 2 25 feet high. An ignition source of wood pallets weighing 750 pounds or Class 2 commodities was used for these 15-minute tests.

The test, designed for freezers and ordinary construction other than freezers, in-volved two phases:

Phase 1 represented ordinary warehouse or manufacturing areas insulated with limited EPS thickness (about four inches) and protected by a wet sprinkler system.

Phase 2 represented freezer/cooler oc-cupancies with significant amounts of EPS (greater than four inches)–which contribute significant combustible material–protected by dry automatic sprinkler systems (which have delayed discharge re-sponse).

The test objectives were to determine the limit of a standard sprinkler system`s ability to protect an ordinary occupancy as well as a building constructed of EPS core sandwich panels and to develop a protection scheme that would protect a freezer insulated with a relatively large quantity of polystyrene. Full-scale Corner Tests using wet and dry sprinkler systems were completed.

Test Conclusions and Recommendations

Based on tests completed to date, extra wet sprinklers must be installed to adequately protect freezers as well as ordinary construction with the dry system. Extra sprinkler heads would have to be strategically placed in a wet system, or dry pendent heads would have to be installed at the ceiling in a dry system.

A future test will be conducted to determine the following: (1) where the new protection scheme will have to be applied, (2) which buildings are adequately protected as is and which need retrofitting, and (3) the minimum wet sprinkler system density needed to prevent fire spread.

For new facilities, the primary recommendation is that FMRC-approved insulated sandwich panels be used where foam plastic insulation is needed. The problem is not evident with FMRC-approved polystyrene products but “sandwich panels containing large thicknesses of EPS present severe challenges for automatic sprinkler systems.”

Corner Testing Reveals Need for Barrier

FMRC-approved thermal barriers are also needed to ensure fire safety in warehouse storage facilities, such as walk-in freezers. In these facilities, FMRC notes, insulation is probably installed in the wall panels, but the roof must also be considered. If the roof is a steel-deck assembly with a gypsum-based core board installed below the polystyrene insulation, the roof is likely fire safe. In fact, the same roof without an FMRC-approved thermal barrier does not ensure fire safety. FMRC notes that its 25-foot full-scale Corner Test has shown repeatedly that steel-deck roofs insulated with polystyrene fail without FMRC-approved thermal barriers. These failures were confirmed with the intermediate-scale FMRC Construction Materials Calorimeter Test.

Of eight experiments done three years ago in which these assemblies were tested, using the White House Test (developed by FMRC in the early 1950s),2 five “passed” and three were called “invalid” for various reasons. The White House Test uses the American Society for Testing and Materials (ASTM) E119 time-temperature curve to demonstrate appropriate performance. “The conclusion that these assemblies are fire safe without thermal barriers is erroneous as far as FMRC is concerned,” says George Smith, manager of FMRC`s Building Materials Section.”Although the White House Test is viable and in fact has been the basis of FMRC`s approval for many other types of roof assemblies, the method is simply not the most appropriate one for polystyrene direct-to-deck, steel-deck roof assemblies.”3

Smith explains that the White House Test does not accurately represent the possibility that these assemblies will breach and vent, essential measures of how the assemblies will behave during a real-world fire, whereas the Corner Test accurately represents a naturally developing fire within a combustible structure. The vastly different results derived from the two tests are attributed to the “geometry and ignition” of a real fire during a Corner Test vs. “a synthetic simulation of a post-flashover fire that happens well into its development stage” in the White House Test–which allows the roof cover to breach rapidly and release combustibles to the environment. “In a real fire involving a typical industrial or commercial building,” FMRC points out, “breaching would not occur at the same time as in the White House Test.” Polystyrene shrinks away from the fire, and, as it does, the burning combustibles and some of the heat escape through the breached roof.

Since EPS core panels have increasingly been used in applications other than those permitted by FMRC standards, such as for wall and ceiling installations, FMRC says “this trend could escalate future loss experience.”

Endnotes

1. The FMRC approval Standard 4880, Class 1 Insulated Wall or Wall & Roof/Ceiling Panels, Plastic Interior Finish Materials, Plastic Exterior Building Panels, Wall Ceiling Coating Systems, and Interior or Exterior Finish Systems, published in August 1994, contains testing protocols for these products. Requirements for both the 25 ft. (7.6 m) and the 50 ft (15.2 m) Corner Tests are provided.

2. Developed by FMRC in the early 1950s, the White House Test exposes a building roof 20 feet wide by 100 feet long to the fire. Except for the roof, the building is constructed totally of noncombustible materials. At one end of the structure, burners are used to produce fire ignition in accordance with the ASTM E119 time-temperature curve.

3. The following test results have been achieved: (1) a steel-deck polystyrene roof with ballasted single-ply roof cover but without thermal barrier did not meet FMRC Standard 4880, (2) a steel-deck polyisocyanurate-insulated roof and ballasted single-ply cover met FMRC Standard 4880, and (3) a steel-deck polystyrene insulated roof with 12-inch gypsum-based thermal barrier and ballasted rubber roof cover met FMRC Standard 4880. n

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