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On the subject of polystyrenes, there are things that should be considered in the design and installation to prevent a fire and its spread.

We have a time bomb in our hands. It can be detonated tomorrow or in twenty years, and, when that happens, we will have a catastrophic situation in Mexico (with people jumping from a burning building, like in the movies). We are building with Expanded Expanded Polystyrene blocks or dry ice in concrete vaults and on top of the panels without fire protection in most commercial buildings, offices, and departments. What are the benefits of doing this: it is cheap, lightweight, has good thermal insulation and absorbs sound and vibration. But there is a problem … it is highly flammable, and that is why it is against all international standards. There are already some examples of tragedies such as the Kiss nightclub in Brazil and the Lobohombo in Mexico.

Self-extinguishing polystyrene? Expanded Polystyrene has a heat emission factor of up to 18,000 BTU / lb (42,000 KJ / kg); Gasoline has a heat emission factor of 19,000 BTU / lb (44,000 KJ / kg). If the expanded polystyrene is exposed to temperatures above 100 ° C it begins to soften and melts at 205 ° C, forming a flammable liquid. The maximum volatilization rate occurs at 364 ° C, where the release of steam will cause rapid flame propagation. Automatic sprinklers are not always effective in confining fire in a small area, that is, if we have even automatic sprinklers and they are located within the space between the ceiling and the suspended ceiling. The expanded polystyrene can be ignited by an open flame generated by other fuels. It tends to shrink away from heat sources before ignition. For this reason, attempts to maintain combustion with a match may not succeed. That is why it is not uncommon to hear some architects and builders refer to expanded polystyrene as self-extinguishing. However, in the case of a building fire, the heat source will be large enough to follow the shrinkage of the polystyrene. This contraction effect allows expanded polystyrene to obtain a relatively low flame propagation value using the ASTM E84 test method. However, a fire involving a small part of the building will maintain a sufficiently intense initial heat source.

The expanded polystyrene on emits a very black and dense smoke that contains oily soot particles that are large and irregular.

The expanded expanded polystyrene emits a very black and dense smoke that contains oily soot particles that are large and irregular in shape. Smoke is an important factor that inhibits the search for an emergency exit and, therefore, increases the risk for occupants. The fumes can also be toxic or have a low oxygen content, while hot soot particles can block the lungs. Flame expanded polystyrene produces more smoke per mass of material than most other materials. Significant amounts of carbon monoxide and styrene monomer are released. Carbon monoxide can be fatal if inhaled for 1 to 3 minutes if they are concentrations of 10-15,000 ppm. Styrene has an odor detected around 25 to 50 ppm and becomes intolerable between 200 and 400 ppm. This warns of the need for immediate evacuation of an area. Eye irritation and nausea may occur at 600 ppm and some neurological damage may occur at 800 ppm.

The maximum volatilization rate occurs at 364 ° C, where the release of steam will cause rapid flame propagation.

In addition to occupant risk, a relatively small fire can result in contamination of an entire area in the case of a food store or electronic equipment. Fire retardant additives may delay fire, but do not significantly affect the burning of expanded polystyrene.

Necessary measures (what is due and not done)

Polystyrene should never be installed exposed. The expanded polystyrene should always be covered with a protective layer. The effective resistance to surface ignition can be with a 9 mm thick gypsum board or a 10 mm plaster, provided that the protective coating is mechanically supported. FM Global recommends a Portland cement plaster with a minimum thickness of 13 mm. Thin finishes, such as plaster coatings, aluminum film, flame retardant paints or intumescent coating applied directly to the expanded polystyrene surface can delay ignition, but once the underlying material softens under the heat of fire, penetration and progressive coating failure.

If the protective coating is not fixed and joins correctly and directly, or to the expanded polystyrene providing an air gap, the failure of the coating can lead to the formation and fall of molten drops, often in flames.

According to the National Fire Protection Association (NFPA) 101 Human Security Code, 2015 in its Section 10.2.4.3, expanded polystyrene should not be used on interior walls and ceilings. NFPA 5000, Construction Code also says the same.

The fire resistance of high-level building structural components is of paramount importance to building occupants and firefighters, given the potential for long evacuation times (section 12.3.3.3.2 of NFPA 1 Fire Code Handbook).

The benefits of using polystyrene: cheap, lightweight, has good thermal insulation and absorbs sound and vibration. But there is a problem … it is highly flammable.

In NFPA 101 HB section 10.2.4.3.2, the prohibition of the use of foamed plastics inside buildings is based on the actual experience of fire in which they have contributed to a very rapid development of fire.

Expanded polystyrene has a flame spread rate of 590. In NFPA 101 Table A.10.2.2 the finish of the inner wall and ceiling is allowed in certain constructions and has a maximum flame spread rate of 200.

According to the International Residential Code (IRC) 2012 Chapter 3, expanded polystyrene requires the following:

  • Must have a flame spread rate not exceeding 75
  • Be separated from the inside of a building by an approved 15-minute thermal barrier of 13mm plasterboard or similar.

Therefore, there are three alternatives regarding the use of Expanded Polystyrene: remove it completely, provide a barrier or use automatic sprinklers.

References: www.fire.tc.faa.gov/pdf/fsr-0239, FM DS 1-57, NFPA 101 HB 2015, European Manufacturers of EPS and Fire Behavior of EPS foam, 18.12.1992, APME Association of Plastic Manufacturers in Europe, www.saferinsulation.org

By: Ing. Mike Wade McDaniel

Article prepared for the magazine against fire February 22, 2018.