PVC or low smoke zero halogen?
In today’s world, buildings with public access require high specification components in their construction. Internal cabling is one of these. Simon Hopkins, Product Manager at Prysmian, examines the importance of low smoke zero halogen cables and what to look out for when stocking and distributing them.
Traditional power and control cable is often PVC. However, if a building needs to pose as little fire hazard as possible to the occupants, PVC cables are not the best option. Granted, PVC cables have many good qualities and will do the job of carrying electrical signals around a building well. There are also varieties available that are flame retardant. However, emission of acid gas and thick black smoke must be also considered as, when burnt, PVC cables give off large amounts of both.
These phenomena can present a real risk to building evacuation, hamper emergency services and present a hazard to personnel and property as well as affecting the continuity of business. Sadly, fires in recent years at Heathrow and Dusseldorf airports, on London Underground and the Channel Tunnel were testament to this.
The best solution for installers is to use a low smoke zero halogen cable, one that emits little smoke and significantly less acid gas. As a wholesaler, it therefore makes sense to know as much as possible about these alternatives as confusion still exists within the marketplace about these products and their capabilities.
PVC cable technology has been around for decades, yet modern buildings incorporate some of the most sophisticated equipment and technology. Surely it makes sense for installers to use a suitably modern and advanced cable to power these systems?
UK Building Regulations tally with this idea. Part B of the Building Regulations (fire safety) states: “The primary danger associated with fire in its early stages is not flame but smoke and noxious gases produced by the fire.” It’s these consequences of fire that cause the majority of casualties and also obscures escape routes and exits. It also spells out: “Measures designed to provide safe means of escape must therefore provide appropriate arrangements to limit rapid spread to smoke and fumes.”
In particular, think about public access buildings possessing large volumes of visitors, such as shopping centres, offices, football grounds, nightclubs and airports. Should fire break out in any of these environments the potential for harm is obvious and if PVC cables are present they will not “limit spread to smoke and fumes.” It follows therefore that installing low smoke zero halogen cables rather than PVC alternatives complies with what Part B calls for.
As mentioned, in a fire PVC cables produce hydrogen chloride acid gas when burnt and can emit in excess of 20% hydrogen chloride acid gas. Should this be inhaled it will result in choking, vomiting and extreme irritation especially if this toxic gas gets into your eyes. In contrast, a low smoke zero halogen cable should emit less than 0.5% hydrogen chloride gas when burnt. Not only this, but PVC cables will also give off dense black smoke which can obscure emergency exit routes and signage, restricting building evacuation. This is the very situation Part B seeks to prevent.
PVC cables present other risks in a fire. They can ignite and spread flame easily, making the fire worse. When this occurs, unprotected cables enable fire to follow their route throughout a building, acting as a conduit for the flames. This in turn can reduce available evacuation routes causing panic and ultimately destroying the building.
In contrast, low smoke zero halogen cables should self-extinguish when the source of flame is removed and will not set light easily due to good resistance to ignition. In addition, when burnt they will only release small quantities of white smoke and virtually no halogen acid gases, reducing the spread of flame in the process. It’s clear to see there is a marked difference between PVC and LSOH cables. If a purchaser requests the latter then it is critical that you supply a product which will perform as intended.
The issue is clouded by the number of acronyms, words and phrases in the market place all related to cables that claim to release small amounts of toxic smoke and gas in the event of a fire. These cables are often called low smoke, LSF or LSOH, as well as many other phrases. It is easy to see how this situation leads to widespread confusion as there is no single agreed phrase or term.
Acronyms such as LSOH are increasingly used as generic descriptions despite actually being a trademark. A problem arises because not all manufacturers use LSOH with the same meaning as the actual trademark owner. This means purchasers can be misled into believing they are buying a low smoke halogen free cable as defined by the appropriate tests, when actually they are getting a cable product that may not perform to the necessary level. Even worse would be to stock and supply a PVC cable masquerading as LSOH, instances of which have been uncovered by the Approved Cables Initiative (ACI).
Used correctly, the phrases ‘low smoke’ and ‘zero halogen’ relate to clearly defined test methods and performance requirements. Low smoke describes a product tested in accordance with BS EN 61034-2. This smoke density test (known as the three metre cube test) measures how much light is transmitted through the smoke produced by burning one metre samples of cable, where 0% means the light is totally obscured and 100% is full light transmission.
A minimum requirement of at least 60% residual light transmission must be achieved. Zero halogen describes a product tested in accordance with BS EN 50267-2-1. Under fire conditions these products must emit less than 0.5 % halogen acid.
It follows that relying on an acronym alone to specify a cable is extremely risky. Instead, you should check compliance with the relevant prescriptive and industry defined British Standards.
Are you stocking the right cable?
- Never place an over-reliance on acronyms alone as this opens up the possibility of stocking and supplying a product without the performance you expect and one that could place lives in danger if installed.
- Always be certain that the cable bought complies with the relevant British Standard.
- If you are unsure of the manufacturer’s reputation check for approval by third party assessors such as LPCB or BASEC.
- If no BS product standard exists, look out for compliance with the low smoke, halogen free and flame retardant BS test standards and requirements as a minimum.
- Be sure to purchase products from a reputable manufacturer and brand.