Are you firesafe?

It is 20 years since the tragedy of King’s Cross, when fumes from melting fixtures and cables caused a significant number of deaths. The rail industry has learned from this and now has some of the most stringent specifications for low-fire-hazard products.

Unfortunately, too many public buildings do not adhere to such standards.

As a conduit manufacturer, Flexicon would always urge that the right material is selected for the right job.

We have PVC conduit in our range, which in the right application is perfectly acceptable. But we would not claim that it is a low-fire-hazard product.

Yet there have been arguments in favour of PVC used in fire prevention. While it has high flame retardency levels, there can be significant problems when a fire takes hold.

Unfortunately the halogens in PVC that bolster its flame retardency produce corrosive by-products – hydrochloric acid is one. Also, the smoke produced can cause a 90% reduction in light emission after just five minutes.

Many well-known high street names are fitting cable, conduit and other fixtures in public buildings with little or no thought about the effects of a fire. This is because nobody monitors the specification of materials in a building from the fire protection angle, and there is no clear guidance on what should be fitted. Ask yourself, “Who specifies what a low-fire-hazard product is?”

Clearly there is a need for guidance, yet too often there is only confusion.

I would argue that we should learn the lessons from the rail industry and plan for a worst-case scenario. The priority is to minimise the effects of a serious fire.

Worst-case plan

Any cables or conduit used within public buildings should, as a minimum requirement, present no danger to the health of people or integrity of property through toxic gas emissions during a fire.

If you are specifying low-fire-hazard performance you should make sure that all four properties – high flame retardency, low smoke levels, low toxicity and zero halogen – can be proven

The term ‘halogen-free’ gives an indication of low smoke levels and low toxicity. It also rules out halogen acid gas emission – a fact that is of interest to insurers since acid smoke can destroy computer equipment and damage the structure of a building.

Tests such as BS 6853 annex B and Naval Standard NES 713 measure toxicity by burning a set amount of material and analysing the gases given off.

Low-fire-hazard materials should also be highly flame-retardant to prevent a fire or limit its development.

Again this can be tested by the Limiting Oxygen Index (LOI). BS EN ISO 4589 determines the percentage of oxygen in the air that would need to be present to support combustion. The higher the percentage the greater the material’s flame retardency.

Approximately 21% of ‘normal’ air is oxygen. Taking the rail industry as a best practice, it demands an LOI of 28% for materials used in overground rolling stock and 34% for underground passenger carriages.

Another test, UL 94, is an insurance underwriters’ standard with flammability classifications HB, VO, V1 and V2. HB allows horizontal burning to a maximum speed and VO is highly flame retardant.

Smoke density is important because people need to be able to see in order to escape. Again the rail industry leads the way in having developed a standard – BS 6853 annex D 8.3, Code of Practice for fire precautions in the design and construction of passenger-carrying trains.

If you are specifying low-fire-hazard performance you should make sure that all four properties – high flame retardency, low smoke levels, low toxicity and zero halogen – can be proven.

There is no point adopting a pick’n’mix approach. Zero halogen does not ensure low smoke and toxicity levels. Equally, a low smoke and fume product may not be self-extinguishing, let alone highly flame-retardant. Both petrol and TNT can be labelled with ‘low smoke’ and ‘zero halogen’.

Perhaps it is time to follow the example of the rail industry and clearly define what ‘low-fire-hazard performance’ means when related to cable management. In the meantime, make sure that your supplier can back their claims and provide performance data on all four aspects of performance.