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

Protecting Your Cables From Fire

Fire prevention in cable runs is one of the most neglected areas during cable installation, yet one of the most important from a legal and health and safety viewpoint. Here, we examine some of the common mistakes committed while installing fiber and how to assess your customer's current set-up.

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

I was going to say your job and yours alone, but many cable runs are shared with other cabling, pipe work and the heavy current people, (though they should not be), so you'll need to liaise the site electricians, IT people and other services like alarms, pipe work etc. 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 as well.

Where there's smoke…
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 not yet removed and still in suit.

There are four types of cable jackets:

  • The old lead-sheathed material left over from the 1940s and 50s. Lead melts easily, revealing paper-covered conductors inside.
  • Poly vinyl chloride (PVC). This is pretty toxic and flammable.
  • Low smoke, zero halogen (LSZH or LS0H) is less toxic and slower to ignite.
  • Plenum grade releases halogen, but requires a higher temperature to ignite than LSZH or PVC.

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

Vital spark
It doesn't take much for fires to start. Causes, common and uncommon, include:

  • Vandalism and deliberate arson.
  • Cigarette butts.
  • Electrical faults (overheating machinery, short circuits).
  • Gas leaks ignited by a spark (light switches and so on).
  • Spontaneous combustion.

Risers and other voids used for cables are often shared with other services, giving flames and fumes plenty of room to propagate. A fire in one confined locality can easily spread throughout a building, so our job is to prevent this.

How it's done — the old way?
Firebreak science has come a long way in recent times. Scientific studies have taught us how fire travels and new materials 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 when ignited, have been developed.

You will still encounter older installations, 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. Some locations still use this scheme.

How it's done- — the new way?
Today's approach is more professional, using a combination of the following:

  • Pads
  • Putty and pillows
  • Expanding foam
  • Cable wraps.

All four classes of products represent the state-of-the-art scientific solutions for each kind of risk, and should be used alongside other precautions such as fire-resistant plasterboard for fire doors and panels. It may be well nigh impossible to make every enclosure airtight for fire and smoke prevention purposes, but it's certainly 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 30mm across (foam is particularly easy to apply and the material is fully cured within 30 minutes at normal room 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.
Where and what?

Common sense will guide you on how to position firebreaks and the main locations are:

  • where trunking, trays and conduit pass through a wall or floor to reach an adjacent room (apply materials on both sides - see Figures 1 and 2);
  • Where ducts enter a building;
  • Anyplace 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, corridors or partitions join.

Common mistakes
Few installations can be considered perfect. Many skimp by providing insufficient firebreaks ("it's not my job") or using non fire-retardant materials (glass, fibre and cardboard are not suitable!). If you are unsure, there are firms who will come and advise or do the job for you (see Yellow Pages) or else you can call in your local fire prevention officer from the fire brigade). Don't assume that the contractors 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 when work is in progress.

Good investment
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 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 also buys time, protecting critical systems and major investment. Finally it also counts toward limiting liability.

Summary checklist
Providing firebreaks is not a one-man task. Consult your health and safety people and the fire officer and involve the people who look after mains electricity, other cabling, pipe-work and building maintenance.
Follow best practice. Take external advice if necessary. Incomplete provision is as useful as no provision at all. Skimping is stupid. Temporary firebreaks must be provided during reconstruction and alterations. Other people's lives depend on your accurate provision.

NM D.S Nagendra, Manager, Premise Networks, KRONE Communications Ltd., India, can be reached at nagendra.ds@krone.com

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