"Is PEX-AL-PEX Hazardous?
Almost any material will deform when heated and burn when exposed to flame, including metals. The issues is the temperature required to cause deformation and how easily the material burns when exposed to flame.
PEX has a maximum application temperature of 95°C/203°F. Temperatures would need to exceed this limit before there would be any risk of deformation that would loosen at a fitting. This temperature is well in excess of what you will see in normal operation. At this temperature, there will be significant failures of other building systems.
PEX will burn, but only at a very slow rate. It has been tested to ASTM E84 which tests the flame propagation and smoke generation properties of materials. Large scale building materials must have a flame spread index of no more than 25 and a smoke generation index of no more than 50. PEX meets these requirements. PEX has been accepted by the national building and mechanical codes. It has been found not to be a fire risk.
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