What are the differences in flame spread between PVC and polyethylene in fires?

The flame spread behavior between polyvinyl chloride (PVC) and polyethylene differs significantly due to their distinct chemical compositions and physical properties. PVC, containing chlorine atoms in its polymer structure, exhibits inherent flame retardancy. When exposed to fire, PVC undergoes decomposition that releases hydrogen chloride gas, which inhibits combustion and slows flame propagation. This results in a relatively slower flame spread rate compared to many other plastics. However, PVC produces dense, toxic smoke containing acidic gases during combustion.

Polyethylene, being a pure hydrocarbon polymer, lacks flame-retardant elements and demonstrates higher flammability. It ignites more readily and spreads flames rapidly due to its higher heat release rate and tendency to melt and drip. The melting behavior of polyethylene creates flowing pools of burning material that can accelerate fire spread to adjacent areas. While polyethylene generates less toxic smoke than PVC initially, it produces greater volumes of smoke as the fire develops.

The fundamental differences emerge from their pyrolysis products: PVC creates char residue that can somewhat inhibit further burning, whereas polyethylene completely volatilizes into combustible gases. These variations make PVC more resistant to ignition but potentially more hazardous in terms of toxic smoke production, while polyethylene presents greater flash fire risk but somewhat less acute toxicity concerns. Understanding these distinctions is crucial for fire safety planning in environments where these materials are present.