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2009-06-25

Are you firesafe?

In this article Ian Gibson, technical director for Flexicon, argues that it is time for clear guidance on the use of low fire hazard (LFH) products.....

  

It is twenty years since the tragedy of King Cross when fumes from melting fixtures and cables contributed significantly to the number of fatalities.  The rail industry has learnt from this and now has some of the most stringent specifications for LFH products.

 

 

 

 

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

 

In fairness to specifiers there is a huge amount of confusion and manufacturers with their own vested interests sometimes muddy the waters even further.  It is perhaps because of this that in all this time standards are often watered down to the point of being meaningless.

 

As conduit manufacturers we 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.  We would not claim however that it is a low fire hazard product.

 

Yet there have been arguments in favour of PVC systems in fire prevention.  While these arguments about flame retardency are true, it does have significant problems if a fire has taken hold.

 

Unfortunately the halogens in PVC that help this flame retardency produces corrosive by products such as hydrochloric acid.  In addition the smoke produced can cause a 90% deterioration in light transmission 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 affects of a fire. This is because nobody polices fire protection for the specification of materials in a building 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 learn the lessons from the rail industry and plan for a worse case scenario.  Clearly the priority is to minimise the affects of a serious fire.

 

So here goes.

 

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.  The term halogen free gives an indication of low smoke 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. 

 

LFH materials should also be highly flame retardant to prevent a fire or limit its development if one does start. 

 

Again this can be tested by the Limiting Oxygen Index (LOI).  BSEN 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 flame retardency of the material.  Oxygen present in normal air is 21%.  Taking the rail industry as a best practice, they demand an LOI of 28% for materials used in over ground 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 up to a maximum speed and VO is highly flame retardant.

 

Finally smoke density is important because people need to be able to see in order to escape.  Again the rail industry leads the way in developing a standard - BS 6853 annex D.8.3, Code of Practice for fire precautions in the design and construction of passenger carrying trains.  A plaque of materials is burnt in a 3 metre cubic chamber.  A graph of smoke opacity against time is plotted which shows the maximum opacity (Ao) and the time taken to reach that opacity.  LFH materials should have an Ao < 0.03.

 

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

  

There is no point adopting a pick and mix approach.  Halogen free does not assure low smoke and toxicity.  Equally a low smoke and fume product may not be self-extinguishing let alone highly flame retardant.  As an example both petrol and TNT can be described as LSOH.

 

So if you are specifying product for a public building make sure that you define what “Low Fire Hazard performance” means.  Plenty of manufacturers are ready to muddy the waters when it comes to cable management. 

 

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 Low Fire Hazard performance.

 

For further information please contact:  Flexicon Ltd, Roman Way, Coleshill, Birmingham, B46 1HG.  Telephone 01675 466900.  Fax:  01675 466901.  Email:  sales@flexicon.uk.com.  Web:  www.flexicon.uk.com


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