A low smoke zero halogen (LSZH or LS0H) cable is an electrical cable whose sheath is difficult to ignite, self-extinguishing, and free of halogen-bearing compounds so it gives off no corrosive gases in a fire. The Dutch abbreviation for the same property is MBZH — moeilijk brandbaar, zonder halogeen.
Why halogen free?
An ordinary PVC sheath contains chlorine. In a fire it releases hydrogen chloride, which forms hydrochloric acid with moisture. That causes two problems:
- For people. Dense, acrid smoke makes escape and firefighting far harder — in most fires the smoke and gases are more dangerous than the flames
- For the building. Acidic smoke settles on steelwork, switchgear and electronics, causing corrosion damage well beyond the seat of the fire
A halogen-free cable produces markedly less smoke and no acid gases. The flame-retardant sheath also limits fire spread along the cable itself — important for vertical bundles, which otherwise behave like a chimney.
Where it is used
Halogen-free cable is standard wherever people gather or where consequential damage would be severe: escape routes, stairwells, tunnels, schools, healthcare buildings, data centres, server rooms and marine installations.
Points to watch
- Classification. In Europe cables fall under the Construction Products Regulation and are graded in reaction-to-fire classes (Aca to Fca) with additional classifications for smoke (s), flaming droplets (d) and acidity (a). Ask for that class, not just for the words “halogen free”
- Not the same as fire resistant. Flame retardant does not mean the cable keeps working during a fire; circuit integrity cables are a separate product
- Penetrations. A good cable through a badly sealed wall penetration still lets fire through. Seal penetrations with a tested collar or intumescent sealant
- Installation. Halogen-free sheaths are generally stiffer and more easily damaged when pulled in; use generously sized conduit and cable lubricant
Related terms
- Electrical cables
- Fire classification
- Fire resistance
- Fire spread
- Compartmentation
- Consumer unit
- Fire prevention
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