No smoke without fire... (Guide to low fire hazard cables)

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 – 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".

Canford cable conformance to BS EN Specifications

BS EN 60332 / IEC 60332 (replaces BS EN 50265)

Part 1 (BS EN 60332-1) applies to single wires (cables) and requires a vertical flame test with a maximum flame climb of 450mm

Part 2 (BS EN 60332-2) applies to very thick copper conductors and is not relevant to audio, video, data and low level control cables

Part 3 (BS EN 60332-3) applies to ‘bunched’ wires (cables). This part of the specification is intended to apply to large cable bundles in building cable ducts. (Additional specifications apply to air conditioning ducts or similar where a forced air supply is present.) Advice should be taken from local regulators to determine if this part applies to your installation.

All PVC, LFH and Special PUR cables manufactured for Canford by Draka, conform to the requirements of BS EN 60332-1 / IEC 60332-1 and can be referred to as "Low Fire Hazard" within the context of this specification (provided the installation is not required to conform to Part 3)

However - for a cable to be described as "Low Smoke and Halogen Free" it must additionally meet the requirements of:

All cables manufactured for Canford by Draka and described by us as "LFH" meet these requirements and can be described as "Low Smoke and Halogen Free".

Note: The higher specification IEC 60332-3-24 test is no longer valid. It has been replaced by the Construction Production Regulation set of "Euroclasses" denoting the different levels of reaction to fire.

Application specification BS 6701:2004

Telecommunications equipment and Telecommunications cabling – specification for installation, operation and maintenance.

All Canford PVC, LFH and PUR cables falling under the terminology "telecommunications cables" (audio, video, data) can be classed as ‘Low fire hazard’ within the guidelines of BS 6701: 2004.

Cable Jacket/Sheath Names and Acronyms with respect to Fire Properties

¹ Products of combustion of polyethylene do not include any halogens, therefore the resulting smoke is halogen-free
² Fillers are the co-polymers used to retard and control the combustion.

Certification should be sought from trade mark holders or users of the above terms that cables conform to the specifications listed.