Even though they are still predominant in the industry, the use of halogenated compounds in wire and cable has decreased over the past several years. Polymers such as PVC are being phased out in certain applications, especially in enclosed, high-density cable applications. Relatively new low-smoke and zero (or low) halogen compounds, which are typically polyolefin based with a heavy doping of inorganic hydrated minerals, give off cleaner smoke when burned. This mineral doping also reduces certain physical properties so the wire and cable industry has attempted to develop low-smoke and halogen-free compounds that have the same or better functionality than the common halogenated compounds currently in use in industrial applications. However, it is important to understand that smoke production and halogen content are not mutually exclusive. Halogenated low-smoke compounds exist as do halogen-free compounds that are not low-smoke. It is always best to consult with wire and cable experts when choosing a cabling solution.
Since the 1970s, the wire and cable industry has been using low-smoke, low-halogen materials in a number of applications. The objective was to create a wire and cable jacketing that was not only flame retardant but also did not generate dense, obscuring smoke and toxic or corrosive gases. Several notable fires over the years (such as the King’s Cross Fire that killed 32 people in London’s underground subway in 1987) increased the awareness of the role that wire and cable jacketing plays in a fire and contributed to a greater adoption of LSZH cables.
With an increase in the amount of cable found in residential, commercial and industrial applications in recent years, there is a greater fuel load in the event of a fire. Wire and cable manufacturers responded by developing materials that had a high resistance to fire while maintaining performance. Low-smoke, zero-halogen compounds proved to be a key materials group that delivered enhanced fire protection performance. Today, low-smoke, zero-halogen cables are being used in applications beyond the traditional transit, shipboard, military and other confined-space applications.
Low smoke, zero halogen has many different abbreviations, and some of the more common ones are listed in Table 1 along with other abbreviations seen in association with LSZH cable. In the U.S., LSZH is the most common term and will be used throughout this paper.
|LSZH||Low smoke, zero halogen|
|LSF||Low smoke, fume|
|LS0H||Low smoke, zero halogen|
|LSHF||Low smoke, halogen free|
|LSNH||Low smoke, nonhalogen|
|NHFR||Nonhalogen, flame retardant|
|HFFR||Halogen free, flame retardant|
|FRNC||Fire retardant, noncorrosive|
|LS||Low, limited smoke|
|ST||Smoke test (limited smoke)|
|FRLS||Fire resistant, low smoke|
Low smoke and zero halogen have different meanings and cannot be used interchangeably. A cable can be low smoke without being halogen free or vice versa. Halogen-free materials typically produce clearer, whiter smoke while chlorinated polymers tend to produce, in part due to their flame resistance, thicker, dark smoke when burned.