Posted 09 July 2019
LSF vs LSHF (LSZH) - There is a Difference!
The main problem facing specifiers and contractors is the confusion over terminology and standards. Is LSHF (Low Smoke Halogen Free) the same as LSF (Low Smoke and Fume)? These terms are all widely used within the cable industry and we still encounter confusion from contractors surrounding the difference between LSF and LSHF cables.
LSF is a somewhat meaningless term applying to products that are often PVC based, which may emit up to 22% Hydrogen Chloride (HCl) gas when burnt and give off black smoke. Hydrogen Chloride gas can be deadly to people and damage sensitive equipment and black smoke can obscure exit routes in the event of a fire. By way of comparison, standard PVC gives off up to 28% HCl.
LSHF cables are those which emit no more than 0.5% HCl when burned. There is a significant difference between the two products and it is vital that specifiers know which they are choosing.
To demonstrate the difference, we filmed a very simple cigarette lighter flame test using a piece of unscreened data cable in both LSF and LSHF versions. The results are startling. The LSF cable very quickly begins to burn and give off black smoke.
By contrast, see how the LSHF cable gives off negligible smoke when exposed to the same heat source. The sheath swells and will eventually burn through in the same way as LSF but it is only producing a tiny amount of white smoke and almost no flame.
There has been a shift in recent years to using newly developed compounds that emit less of the harmful gases, particularly halogens, but still perform well in other respects. The difficulty for the cable buyer is that there are no specific standards for LSF cables. Ordinary PVC emits approximately 28% HCl, whilst modified PVC could give off a massive 22% HCl and still be sold as LSF.
If you want to be absolutely certain of what you are installing you should insist on a cable that uses insulation and sheathing materials that do not emit any Halogens and have reduced smoke emission properties. These are termed LSHF (Low Smoke Halogen Free), LS0H, LSZH (Low Smoke Zero Halogen) or sometimes OHLS (Zero Halogen Low Smoke). These products must emit no more than 0.5% HCl.
Also, don’t accept standard PVC cables over-sheathed with an LSHF jacket or cables with PVC insulation. When the jacket burns through, the PVC inner sheath or insulation will give off poisonous gases in just the same way as if the LSHF jacket wasn’t there! Another common misunderstanding is that LSF or LSHF cable is also flame retardant. This is not necessarily true. The cables may spread the fire even though minimal fumes are being emitted.
Some customers are opting for LSF cable (Low Smoke and Fume) over standard PVC cable and as a result we are stocking many of the popular alternatives to Belden style cables in LSF.
The compounds now widely used in the market are modified PVC which still emit poisonous halogens and smoke - just slightly less of them. If you buy these products from us or another supplier remember they are PVC based and should be regarded as only slightly better than standard PVC in the event of a fire.
Correctly specified, both products offer a good solution but it’s crucial to know when and where it’s appropriate to use them. Don’t be confused or take the risk – if the job specifies LSHF, then LSF cables will not perform to the correct level in the event of fire. You could be putting lives at risk.