LSZH vs LSF Cable
What’s the big difference?
There is a common misconception that LSF and LSZH cables are the same, however this is not the case and any confusion between the two could be life threatening in the event of a fire. Burning PVC and other cable compounds produce a number of chemicals, including hydrogen chloride (HCI), which is highly toxic.
When mixed with water, HCI forms hydrochloric acid, a toxic and corrosive substance. In the case of PVC, as much as 30% of the emissions can be HCI.
BS EN 60754 stipulates that emissions of HCI by LSZH cables must not exceed 0.5%.
Unlike PVC cables and those made of other compounds which produce vast amounts of dense black smoke, toxic fumes, and acid gas when exposed to fire, LSZH cables produce very low levels of smoke and toxic fume and no acid gases. For this reason, they are often specified for indoor use, especially in public areas, poorly ventilated areas and other hazardous environments. This includes, but is not limited to cars, aircraft, trains and ships. LSZH sheathed cables are also commonly used across tunnels and underground networks.
According to Part B of The Building Regulations, a leading planning and building regulations resource for England and Wales:
“The primary danger associated with fire in its early stages is not flame but the smoke and noxious gases produced by the fire. They cause most of the casualties and may also obscure the way to escape routes and exits. Measures design to provide safe means of escape must therefore provide appropriate arrangements to limit the rapid spread of smoke and fumes.”
Make sure you use the correct cable as per the specifications of your job.
LSF cables are manufactured using PVC compounds. If they are labelled as low smoke and fume it means that the manufacturer has modified the compound with various additives in order to reduce (not eliminate) smoke and HCI (Hydrogen Chloride) emissions. There are no standards governing LSF cables, resulting in them being found to emit HCI levels in excess of 20% when burning.
Burning PVC has been found to reduce visibility in the surrounding area by as much as 50% within 10 minutes, further decreasing to just 10% visibility within 30 minutes.