LSZH

LSZH (Low Smoke Zero Halogen) is a material classification for wire and cable insulation and jacketing: compounds that emit little smoke and no significant halogen acid gas when they burn. Instead of halogenated polymers such as PVC, LSZH compounds use halogen-free polyolefins loaded with mineral flame retardants — typically aluminium hydroxide or magnesium hydroxide — which release water vapour when heated.

The same classification travels under several abbreviations:

• LSOH / LS0H — Low Smoke Zero Halogen (the “0” standing in for “zero”)
• LSFH — Low Smoke Free of Halogen
• LSHF — Low Smoke Halogen-Free (the form IEC itself uses in the IEC 62821-1 material designation “LSHF/D”)
• OHLS — Zero Halogen Low Smoke (rare; the “O” reads as zero, with the word order reversed)

The classification matters because halogenated jackets, PVC above all, evolve dense smoke and corrosive, toxic gases in a fire. IPC-HDBK-620 notes that burning PVC releases toxic hydrogen chloride gas, which forms hydrochloric acid when inhaled, and describes PVC’s outgassed fire products as hazardous, corrosive and toxic. Corrosive combustion gases also damage equipment and building structures. LSZH cable is therefore specified for enclosed spaces where people and equipment share the fire environment — ships, rail vehicles, tunnels, data centres and other poorly ventilated installations.

LSZH performance is defined by test standards rather than by the acronym itself: IEC 60754-1 covers determination of the halogen acid content of gases evolved during combustion of cable materials (IEC 60754-2 covers their acidity and conductivity), IEC 61034 covers measurement of the smoke density of cables burning under defined conditions, and cable specifications such as IEC 62821 set requirements using these test methods. Note that LSZH addresses smoke and gas emission, not fire survival, and it is not interchangeable with the North-American plenum (CMP) rating. The high mineral-filler loading can also reduce jacket mechanical properties compared with conventional compounds, so bend radius and installation stress deserve extra attention.