Fire Damaged Effects on Structured Cabling

Occasionally unfortunate accidents happen to companies and their buildings become victims of fire.

Once damage to the structure of the building is assessed, the company has to determine the state of the communication system. Quite often during this situation the cabling and/or patch panels are visibly effected by the fire, logically suggesting that the company replace the damaged components.

However we often have to deal with a situation where the cabling system in total shows little visible damage and there is no way of telling how hot the fire was or how close the flames and smoke came to any of the cables, panels, or connectors.

Damage to cables can be assessed in basically two different circumstances. If the cable exhibits char and it is obvious that the cable was burned, then it can be understood that this cable is damaged.

Another circumstance that can signal a damaged cable is if the cable does not appear to be charred but the cable jacket has been deformed from its original shape at the time of installation. This can occur due to excessive temperatures resulting from the fire, then this cable is to be considered damaged as well.

Connectors and patch panel damage is best judged by viewing the residue of smoke ashes. This physical evidence confirms that smoke had filled the room and that particles may have affected the PCB boards of the equipment in that room. Smoke particles can build up on electrodes and take in water molecules that will enhance the conductivity of the smoke particles and therefore could cause long term problems (excessive crosstalk) and possibly damage connectors and patch panels.

Due to this phenomenon, evidence of smoke particles will require the connectors and patch panels to be replaced.

Corrosion Related Equipment Failures

There are damage mechanisms associated with real fires that are of greater consequence than acid gas generation and metal loss. With respect to corrosive components in the smoke, acid gases are important, but ionic contaminants associated with fillers, flame retardants, colorants, processing aids and/or impurities in the polymers, or by-products of the polymerization reactions, can also be important.

The most common cause of equipment malfunction following exposure to smoke from cable combustion is not loss in thickness of structural metals or metal circuitry from direct deposition of corrosive gases but rather electrical shorts and arcing that cause cross-talk and malfunctioning components. The low insulation resistance associated with smoke-related contamination leads to metal migration (dendrites), electrolytically corroded conductor lines (quite distinct from the direct corrosion caused by deposition of corrosive smoke on conductors), and other electrochemical degradation processes.

The full array of contaminants from the smoke includes the halide gases but also includes other ionic contaminants, organic gases, and, in some cases graphitic carbon. High humidity exacerbates the effects of ionic contaminants. However, if graphitic carbon is formed in a fire, it has been found to be conductive at all humidity levels.

Post Fire Guidelines for Structures Cabling System

In order to determine the damage of a fire to a SCS, the following can be used as guidelines while visiting the site in question.

The first recommendation is to have a total change out of all cables, connectors and patch panels if possible, especially if the installation is small, say less than 300 outlets. It is probably more expensive for the insurers to call out a loss adjuster. If a total change out is not possible, then the guidelines below can be used.

1. Cables can be damaged in different ways. If the cable was exposed to the flames and is charred, then the cable has to be replaced. Also, if there exists no evidence of charring, but the heat from the flame has changed the geometry of the cable jacket to a different shape than what was installed, then the cable must be replaced. These effects of a fire must be searched for down the length of the horizontal run and backbone run. A deformed cable will change its transmission characteristic (its SRL and RL will degrade and possibly other parameters as well). The main point is that if the cables are different (due to deformity) from its original manufactured or installed (before the fire) state, or there are signs of char due to fire, then the cables are no longer acceptable.

2. As for patch panels and connectors, the problem is the same as equipment reliability:

The presence of smoke particles raises an issue with corrosivity of the components since most connectors/patch panels are PCB based. Even if the cables are fine, the connectors and patch panels are questionable in terms of long term integrity. So if there is physical evidence of smoke particles around the vicinity, then the connectors and patch panels in those areas are considered damaged and should be replaced.

3. If the cables do not appear to be charred but evidence of geometric distortion has occurred, then the transmission parameters will have changed. In order to provide interested parties with evidence of this situation, performance tests from a hand held tester taken before the fire should be compared to performance tests taken after the fire. Any difference in outcomes will be reason to discontinue any guaranteed performance until the effected links are changed.

Flood Damaged Effects on Structures Cabling

Premises wiring cables are, as their name implies, intended for use in indoor applications where they would not be expected to be subjected to significant amounts of liquid water exposure. Unlike outdoor cables, premises cables don’t incorporate materials or constructions intended to block and/or minimize the effects of water penetration.

The risk of exposing premises cables to significant quantities of water is the potential for liquid water penetration into the interior of the cable. The presence of water in these cables will immediately and adversely affect the electrical transmission properties of the cables, including capacitance, signal attenuation (loss), crosstalk and balance.

Longer term, the presence of water has potential to cause corrosion of the copper conductors at any sort of insulation defect, even the occasional microscopic insulation pinholes which are inherent in any plastic insulated hole cable. Therefore, there is a high probability that either short-or long-term performance problems, or both, will occur when water is present in the core of a premises wiring cable.

While the above discussion applies to any premises wiring cable, these issues are even more critical for very high performance cables such as Category 5 and 6 LAN cables. For the reasons discussed, the high performance of Category 5 and 6 cables cannot be guaranteed when water exposure as described above has occurred.

Water In Telecommunication Cables

The effect of water on cables is becoming an important issue to the companies because of the increasing use of high-speed digital services. The three major effects of water on copper cables and wires are:

– Corrosion of the conductors
– Increase capacitance and attenuation
– Decreased impedance