Expanded polystyrene (EPS), commonly known as Styrofoam, is a lightweight plastic material widely used in packaging and insulation. Made from the polymer polystyrene, an organic compound derived from petroleum, the material is inherently combustible. Untreated Styrofoam is highly flammable and presents a significant fire hazard, capable of quickly fueling a fire.
The Flammability of Untreated Polystyrene
Standard, untreated expanded polystyrene is composed of long chains of hydrocarbons. This chemical structure is similar to that of many fuels, making the material readily combustible once it reaches its ignition temperature. The physical structure of Styrofoam further compounds this risk, as the material consists of approximately 95% trapped air within its foam matrix. This air-filled structure provides an abundant source of oxygen, accelerating the combustion process. Once ignited, the hydrocarbon chains rapidly break down, sustaining the flame more easily than materials like wood or paper.
The low density and high surface-area-to-volume ratio of foam packaging mean the material catches fire quickly. The heat from a small flame or spark can rapidly raise the temperature of the thin polystyrene walls to its ignition point. This ease of ignition makes standard packing foam a particular hazard in storage areas or when used near heat sources.
How Styrofoam Burns and Melts
When exposed to heat, Styrofoam undergoes a process involving both melting and combustion. The material first softens and liquefies at relatively low temperatures, around 140°C, before ignition. This melting results in hot, flaming droplets of liquid plastic that can drip down and spread the fire to lower surfaces, creating a secondary hazard. The combustion process is incomplete, leading to the production of thick, black, noxious smoke.
This dense smoke contains volatile compounds, posing a greater threat than the flames themselves. Toxic byproducts released include styrene monomer, a known irritant, alongside dangerous gases like carbon monoxide. In a confined space, the rapid accumulation of this toxic smoke significantly reduces visibility and quickly causes incapacitation, making evacuation difficult. Over 57 chemical by-products have been identified during the combustion of expanded polystyrene.
Fire Retardants and Safety Grades
To mitigate fire risk in applications like building insulation, polystyrene is often treated with specialized chemical fire retardants. These treated materials, commonly used in Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS) insulation boards, are referred to as “FR-Grade.” Historically, hexabromocyclododecane (HBCD) was common, but modern alternatives, including non-halogenated and polymeric flame retardants, are now being introduced due to environmental concerns.
These treated materials are not fireproof but are classified as “self-extinguishing.” The retardant additives raise the material’s ignition temperature and reduce the rate of flame spread. Once the direct ignition source is removed, the treated foam will stop burning, preventing the fire from spreading through the insulation. This self-extinguishing property allows the materials to meet stringent fire safety requirements for construction, distinguishing them from untreated packaging foam.
Storage and Fire Safety Guidelines
Because of its flammability, the proper handling and storage of Styrofoam are important for safety. Untreated packaging foam should be kept away from all potential heat sources, including open flames, space heaters, and hot light fixtures. Burning Styrofoam in a home fireplace or outdoor pit should be avoided, as this releases toxic fumes into the air.
The material should be disposed of according to local waste management guidelines, often involving placement in the regular trash. Reusing the foam, such as saving packing peanuts or repurposing large blocks for craft projects, is a better alternative. If the material is used in construction, ensure it is an approved, fire-retardant grade and fully covered by a fire-resistant barrier, such as drywall, as required by building codes.