PVC (polyvinyl chloride) is a thermoplastic material, which comprises 57% chlorine (obtained from industrial grade salt) and 43% carbon (obtained mainly from oil/gas through ethylene). This flexible material is commonly used as a replacement for copper and aluminium pipes in several areas. PVC Pipes are used for plumbing and drainage, replacing metal piping. PVC is also used as insulation on electrical cables, such as those used in teck. For this purpose, PVC needs to be plasticised.
Flexible PVC-coated wire and cable for electrical use has traditionally been stabilised with lead, but these are being replaced with calcium-zinc-based systems. In a fire, PVC-coated wires can produce hydrogen chloride fumes; the chlorine serves to scavenge free radicals and is the source of the material's fire-retardant properties. While hydrogen chloride fumes can also pose a health hazard, they dissolve in moisture and break down onto surfaces, particularly in areas where the air is cool enough to breathe and is not available for inhalation.
Frequently, in applications where smoke is a major hazard (notably in tunnels and communal areas), PVC-free cable insulation is preferred, such as low-smoke, zero-halogen (LSZH) insulation. Plastic pipes exposed to fire will react differently according to the type of plastic they are made from. Some will soften and then char as the fire progresses; others will soften and melt. If not properly fire-stopped, these pipes may burn out, leaving a passage for fire to spread into adjoining rooms and allowing a fire to quickly spread.
Fire collars and fire sleeves with intumescent materials are typically used to seal the pipe shut, completely preventing the fire from passing through. Because different types of plastic can react to fire in different ways, you must ensure the fire collar you choose is tested and approved for the type of plastic or make of pipe you are using.