Many building projects now call for the use of cables that, in the event of a fire, are less hazardous to people when they burn. There are two key features – reduced smoke emission to minimise hazards from smoke inhalation and aid evacuation, and no or minimal halogen combustion products which are highly toxic. These must not be confused with Fire Retardant cables, which are designed to continue to perform for extended periods in the event of fire eg. in voice evacuation systems, and have an altogether quite different and much more complex construction.
The original cause of the problem is that the most commonly used cable insulating and jacketing material is PVC. Advantages are its cheapness, and that, with the addition of various elastomers, it can be made extremely flexible and remain so at lower temperatures. Disadvantages are that it’s nasty when it burns, as it produces considerable amounts of smoke and releases toxic halogen compounds.
For deployable cabling therefore, PVC remains the main jacketing material. For lowest cost there is plain PVC, for improved flexibility there is “Arctic” grade – most commonly used on mains cables – and then there are more complex proprietary compounds used on many audio and video cables where exceptional flexibility is required and where a “semi-matt” (“satin”) surface finish is required.
So, to create cables that are less hazardous in the event of fire, various compounds have been developed. These are typically described as “low smoke, zero halogen” or “low fire hazard”. The bad news is that they lack flexibility and discolour easily – but as cables made from these are going to be in ducts or ceiling voids, that’s not really a problem. They are obviously not recommended for deployable use!
Some confusion is caused as a result of some manufacturers using four-letter acronyms for these types which they have registered as trademarks, but which have become commonly used to describe the cable style. “LSOH”, the best known, is a trademark of Pirelli General plc, one of the earliest developers of this kind of material. Most other meaningful combinations of these letters (including Z for zero or N for no instead of O) are also registered trademarks. Consequently Canford cannot use these in the catalogue – instead we use our own mark – “LFH”.