Fighting fire

Fire is such a menace that everyone knows the risks involved and how to avert them. Or that's the received wisdom. In the real world it doesn't quite work like that, especially when it's unclear who has responsibility for fire precaution.

Positioning fire extinguishers and marking fire exits is clearly a task for your facilities manager, while fire doors and other elements of prevention should have been correctly designed into the premises. But fire doesn't play by the rules and takes any route it finds. Flames, smoke and noxious fumes can race along cable ducts and the voids found in suspended ceilings and false floors if unhindered by firebreaks, and assigning responsibility for safety precautions here may be debatable. So assume that it's your job!

I was going to say your job and yours alone but many cable runs are shared with other building services so you'll need to liaise with other trades. Anything to do with false floors and ceilings will affect building maintenance, so you'll need to involve them as well.

Fire prevention will also bring you into contact with the person responsible for health and safety, and there should be a designated fire officer. There will doubtless be insurance implications too, so you need to speak to whoever looks after these matters.

Fire can propagate along cable runs; it can also start there. Many types of cable are flammable, particularly older ones with pvc jackets. You may not install them for active use today, but there may be redundant pvc cables still in situ.

There are in fact four types of cable jacket that you may encounter:

• the old lead-sheathed material left over from the 1940s and 50s. Lead melts easily, revealing paper-covered conductors inside;
  
• polyvinyl chloride (pvc) – this is pretty toxic and flammable;
  
• low smoke, zero halogen (lszh or lsoh) – less toxic and slow to ignite;
  
• plenum grade – releases halogen, but requires a higher temperature to ignite than lszh or pvc.

As the responsible installer, it's your job to make sure that you know the type and location of all cable materials and to ensure that you comply with regulations.

It doesn't take much for fires to start. Causes include:

• vandalism and deliberate arson;
  
• discarded cigarette ends;
  
• electrical faults;
  
• gas leaks ignited by a spark;
  
• spontaneous combustion.

Risers and other cable voids are often shared with other services, giving flames and fumes plenty of room to propagate. A problem in one confined locality can easily spread throughout a building.

Firebreak science has come a long way in recent times. Scientific studies have taught us how fire travels and new materials have been developed, such as intumescent products, which expand in the presence of heat to block the passage of fire and smoke, and low or zero-halogen cable insulation, which does not produce halogen once ignited.

You will still encounter older installations though, in which the sole impediment to fire in cable ducts was bags of incombustible mineral products, such as asbestos dust or vermiculite. Where cables passed through walls and ceilings, vermiculite compound was mixed with glue and forced into all gaps around the cables.

Today's approach is more professional, using a combination of pads, putty and pillows, expanding foam and cable wraps. All four classes of product are scientific solutions for each kind of risk, and should be used alongside other measures such as fire-resistant plasterboard for doors and panels.

It may be well-nigh impossible to make every enclosure airtight for fire and smoke prevention purposes, but it's possible to use intumescent strips and pads that expand in the presence of heat and thus block off small gaps. Fireproof putty and expanding foam will fill gaps up to 30 mm across (foam is particularly easy to apply and the material is fully cured within 30 minutes at normal temperature). Larger holes can be blocked with pillows, held in place with chicken wire if necessary. Finally, cable wraps made of incombustible material can be used where warranted.

Common sense will guide you on how to position firebreaks:

• where trunking, trays and conduit pass through a wall or floor to reach an adjacent room (apply materials on both sides – see below);
  
• where duct enters a building;
  
• where cables leave a building;
  
• below computer-type false floors, going from one room to another;
  
• partitions separating one zone of open-plan offices from another;
  
• above suspended and false ceilings, where rooms join.

Few installations can be considered perfect. Many skimp by providing insufficient firebreaks or using non fire-retardant materials – glass fibre and cardboard are not suitable! If you are unsure, there are firms that will come and advise or you can call in your local fire prevention officer. Don't assume that the contractors will have made a thorough check; that's your job. Fires don't wait until cabling is complete either, so you must put in temporary fire stops, even during work in progress.

Firebreaks are not an option, they are essential. Not only do they prevent the spread of flames and fire, they also block smoke and fumes, which are even more potent killers.

A single firebreak left undone could result in death, making the provision of firebreaks in cable runs a vital investment. Not only does this save lives, it buys time, protecting critical systems and major investment. Finally, it also counts toward limiting liability.