Is your structured cabling fire proof?

BANGALORE, INDIA: Fire Hazards and its regulations is a topic every facility manager is or should be familiar with today. Professional organizations and bodies have done plenty of research in the last few decades.

Commercial buildings today have to adhere to fire safety norms and be equipped with fire preventions methods. It is mandatory to obtain safety certificates from relevant authorities before allowing possession of the building. However, there are still fire accidents, loss of lives, destruction and damage to property and infrastructure even with all these norms are practices.

A recent report from an office fire incident had the following startling revelations:

The building was constructed as per fire norms, and all relevant pre-requisite certifications were in place.
The communications cabling was done with Low Smoke Zero Halogen Jacketed Cables.
Fire sprinklers and fire fighting equipments were in perfect working conditions.
And yet,
Smoke emission from the building was more than expected.
Fireballs were seen coming out of the ceiling void.
Firefighters took almost five hours to contain the fire.

A forensic study showed that the fire originated from one of the work locations and spread rapidly through the communication cable all the way to the ceiling through a hole that was built with the intention of cable routing. The fire spread to the void space between the original and false ceiling that resulted in deformation of trays and a thick residue was found due to the intense heat.

The three factors that account for loss of human lives due to fire are:

Heat: High temperature cause fatal burns
Smoke: Reduces vision making if difficult to find the escape route.
Toxicity: Carbon Monoxide is fatal, along with numerous other harmful chemicals and emissions which cause eye irritation and burning.

Reports here clearly showed that the communications cabling and the cable jackets were made of Low Smoke Zero Halogen Materials, which intensified the fire.

SIMULATION EXPERIMENT
Common LAN cable constructions include compounded PVC or compounded polyolefin (non-halogen) sheathing over polyethylene or polypropylene based insulations on the copper conductors. Non-halogen cable constructions are often designated LSZH (for Low Smoke Zero Halogen). Typically, LSZH polyolefin base polymers have high fuel loads and are highly combustible. Therefore, they are compounded with metal-hydrate fillers to delay ignitability until the water of hydration is exhausted resulting in vigorous combustion.

Full-scale fire tests simulating installation practices were conducted at BRE/FRS (Building Research Establishment/Fire Research Station) Cardington. The test program was designed to support the development of new performance data for hazard assessments, international fire test protocols and fire safety engineering.

Earlier tests were carried out in a burn-room/concealed-space re-burnable structure with a nominal 1-megawatt wood crib source-fire. The later tests used a nominal 1-megawatt gas burner. Fire scenarios, ventilation conditions, and LAN cable designs and configurations were varied. Fire performance measurements included mass loss, pressure differentials, lateral flame spread, heat flux, vertical temperature profiles, smoke opacity, heat release, CO and CO2 generation and O2 depletion. Tests were documented with still and video photography in both IR and white light. Most data were logged electronically (about every 10 seconds) for real-time on-line graphical monitoring, and then stored in spreadsheet formats to facilitate statistical analysis and computer modeling.

LSZH cables that pass IEC 332-1 and IEC 332-3 ignited readily and burned the full length of the concealed space configuration. A large fireball developed on the horizontal cable ladder and a pool of fire formed on the suspended ceiling beneath the cable ladder in the concealed space. Ceiling tiles often fell out during tests.

Under the same full-scale test conditions, LAN cables that pass NFPA 262 (Steiner Tunnel) test criteria showed no sign of flame spread and generated little smoke.
Other related tests were conducted in the intermediate-scale Steiner Tunnel and in the small-scale tube furnace/smoke box apparatus developed for the British Cable Makers Confederation (BCMC). The cable fire performance (flame, spread, smoke and heat release) data from the Steiner Tunnel was relatable to the BRE/FRS full-scale simulations. The data from the IEC 332-1 and IEC 332-3 tests was not relatable.

Surprisingly, dense dark smoke and forceful explosions occurred with just one gram of polyolefin cable materials from the LSZH cables in the BCMC small-scale apparatus tests. The PVC cable materials produced very little smoke and no explosions in the same small-scale BCMC tests. These explosions may relate to flashover phenomena.

REPORTS
From various studies & simulation experiment the following results have arrived.

Ceiling and floor concealed spaces (voids) in commercial buildings were increasingly being used for utilities and ventilation. This design approach helps maximize flexibility in meeting changing tenant churn requirements.

Installing services in concealed spaces provides convenient access, easy alterations, lower construction costs and energy conservation for heating, ventilation and air conditioning (HVAC).

If these concealed spaces contain combustibles, they are potential sites for the undetected generation and movement of fire and smoke.

Construction products exposed in the concealed spaces have been required to be (a) fire partitioned, or be (b) very low in fuel-load and combustibility, or be (c) protected by either fire resistant coverings or fire extinguishment systems.

Concealed spaces being filled with multiple generations of data communications cables with low or unknown aggregate fire performance.

The Simulation Experiment results and IEC 60332-1 & 60332-3 do not match.

CONCLUSIONS
1.The data obtained in the Steiner Tunnel was relatable to the full-scale BRE/FRS simulations.
2.The flame spread, heat release and smoke opacity results for exposed Plenum (PVC) cable were significantly lower than results for exposed LSZH and CMX cable.
3.For LSZH cables, the high temperatures, high heat release rates, flame spread, fire-balls, pool fires and tube furnace explosions were unexpected considering their extensive use in concealed spaces in commercial buildings.
4.There was no discernible difference in toxicity between the fluoropolymer category of materials used in CMP cables versus polyolefin and PVC categories of materials used in the LSZH cables per NEMA data.10.

The author is product manager, Enterprise Networks India at TE Connectivity.