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PVC cable insulation and polystyrene insulation

Safety message​

The service life of insulated cables in the above situation can be severely reduced, with many years passing before noticeable deterioration occurs.

Household electrical wiring should be inspected and replaced regularly by a qualified electrician, ensuring they are aware of any polystyrene insulation in the property, including cavity wall insulation.

Further information

How this fire happened


The husband and wife who owned this property had taken great care over the maintenance of it and were extremely house proud. 

Early one Sunday evening, the female occupier was on her own in the house when she heard her smoke alarm activate. She went to investigate and saw wisps of smoke coming out of the loft hatch on the landing.


She immediately phoned the fire service and left the property, shutting the door behind her.

When fire crews arrived they discovered a small fire in the loft, which they extinguished with a hose reel.

During this time the husband returned, to see smoke coming out of his house and the fire service outside his house, his fears subsided once he saw his wife calmly talking to fire officers outside the property.

Electrical wiring

Electrical wiring had been run across the loft space with sheets of polystyrene insulation laid over the top.

Over a period of years the cable insulation became coated in polystyrene, not due to thermal effects but rather as a result of “plasticiser migration”.

There was a reaction between the plasticiser in the PVC insulation and the polystyrene, whereby the plasticiser migrated out of the PVC, softening the styrene which adhered to the PVC, leaving a brittle cable that cracked and split, exposing live conductors which caused a fire involving the timbers within the loft space.

But for the activation of the smoke detector aiding early intervention by the fire service, the damage to the couple’s home could have been far more severe.

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