Fire Performance of Electric Cables

Often the most effective flame retardant cables are halogenated as a outcome of both the insulation and outer Jacket are flame retardant however when we need Halogen Free cables we discover it is often solely the outer jacket which is flame retardant and the internal insulation is not.
This has significance as a end result of whereas cables with a flame retardant outer jacket will often pass flame retardance exams with exterior flame, the same cables when subjected to high overload or prolonged short circuits have proved in university checks to be extremely flammable and can even begin a fire. This effect is understood and published (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is perhaps stunning that there aren’t any widespread check protocols for this seemingly frequent event and one cited by each authorities and media as cause of constructing fires.
Further, in Flame Retardant check methods corresponding to IEC60332 elements 1 & three which make use of an exterior flame supply, the cable samples are not pre-conditioned to regular working temperature but tested at room temperature. This oversight is essential particularly for power circuits as a end result of the temperature index of the cable (the temperature at which the cable material will self-support combustion in normal air) might be considerably affected by its beginning temperature i.e.: The hotter the cable is, the more simply it’s going to propagate hearth.
It would appear that a need exists to re-evaluate current cable flame retardance check methods as these are commonly understood by consultants and customers alike to supply a dependable indication of a cables capacity to retard the propagation of fireside.
If we can’t trust the Standards what do we do?

In the USA many constructing standards don’t require halogen free cables. Certainly this isn’t as a outcome of Americans are not wisely informed of the hazards; rather the approach taken is that: “It is healthier to have highly flame retardant cables which don’t propagate fireplace than minimally flame retardant cables which can unfold a fire” – (a small hearth with some halogen may be better than a large fireplace with out halogens). One of one of the best methods to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and lots of countries around the world adopt a special mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the reality is quite completely different: Flame propagation tests for cables as adopted in UK and Europe can arguably be mentioned to be much less stringent than a few of the flame propagation exams for cables in USA resulting in the conclusion that widespread tests in UK and Europe could simply be exams the cables can move rather than tests the cables should pass.
Conclusion

For most flexible polymeric cables the selection remains right now between high flame propagation efficiency with halogens or decreased flame propagation performance without halogens.
Enclosing cables in metal conduit will scale back propagation at the point of fire but hydrocarbon primarily based combustion gasses from decomposing polymers are likely propagate through the conduits to switchboards, distribution boards and junction packing containers in different elements of the building. Any spark such because the opening or closing of circuit breakers, or contactors is more likely to ignite the combustible gasses resulting in explosion and spreading the hearth to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide an answer, there’s often no singe good reply for each set up so designers want to judge the required efficiency on a “project-by-project” basis to resolve which know-how is perfect.
The primary importance of fireplace load

Inside all buildings and tasks electric cables provide the connectivity which retains lights on, air-conditioning working and the lifts operating. It powers computers, workplace tools and provides the connection for our telephone and computers. Even our mobile phones want to connect with wi-fi or GSM antennas which are linked to the telecom network by fiber optic or copper cables. Cables ensure our security by connecting

hearth alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, hearth sprinkler pumps, smoke and heat detectors, and so many other options of a contemporary Building Management System.
Where public security is essential we regularly request cables to have added security features such as flame retardance to make sure the cables don’t simply unfold fire, circuit integrity throughout fireplace in order that important fire-fighting and life safety gear keep working. Sometimes we may recognize that the combustion of electric cables produces smoke and this can be poisonous so we call for cables to be Low Smoke and Halogen Free. Logically and intuitively we think that by requesting these particular properties the cables we purchase and install will be safer

Because cables are put in by many different trades for various functions and are principally hidden or embedded in our constructions, what is usually not realized is that the various miles of cables and tons of plastic polymers which make up the cables can represent one of the biggest hearth hundreds in the constructing. This level is definitely worth considering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are mostly based mostly on hydrocarbon polymers. These base materials aren’t typically flame retardant and naturally have a excessive fire load. Cable manufacturers make them flame retardant by adding compounds and chemicals. Certainly this improves the volatility of burning however the gasoline content material of the bottom polymers stays.
Tables 1 and 2 above examine the hearth load in MJ/Kg for frequent cable insulating supplies in opposition to some frequent fuels. The Heat Release Rate and volatility in air for these supplies will differ but the gasoline added to a hearth per kilogram and the consequential quantity of heat generated and oxygen consumed is relative.
The quantity in kilometers and tons of cables installed in our buildings and the related fireplace load of the insulations is appreciable. This is especially important in initiatives with long egress instances like high rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When considering hearth security we must first perceive an important components. Fire consultants inform us most fireplace associated deaths in buildings are caused by smoke inhalation, temperature rise and oxygen depletion or by trauma attributable to jumping in making an attempt to escape these effects.
Smoke

The first and most important aspect of smoke is how a lot smoke? Typically the larger the fire the more smoke is generated so anything we can do to scale back the spread of fire may also correspondingly scale back the amount of smoke.
Smoke will comprise particulates of carbon, ash and other solids, liquids and gasses, many are toxic and flamable. In particular, fires in confined areas like buildings, tunnels and underground environments cause oxygen levels to drop, this contributes to incomplete burning and smoldering which produces increased quantities of smoke and toxic byproducts including CO and CO2. Presence of halogenated materials will launch toxic Halides like Hydrogen Chloride together with many different toxic and flammable gasses within the smoke.
For this purpose common smoke checks performed on cable insulation materials in massive three meter3 chambers with plenty of air can present misleading smoke figures as a result of complete burning will usually launch considerably less smoke than partial incomplete burning which is likely in apply. Simply specifying IEC 61034 with an outlined obscuration value then thinking this will provide a low smoke setting during fire could sadly be little of assist for the individuals really involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise

It is regarding that Europe and other international locations adopt the concept of halogen free supplies with out correctly addressing the topic of toxicity. Halogens launched throughout combustion are extremely toxic but so too is carbon monoxide and this is not a halogen gasoline. It is widespread to call for halogen free cables after which allow the use of Polyethylene as a end result of it’s halogen free. Burning Polyethylene (which could be seen from the table above has the best MJ gas load per Kg of all insulations) will generate almost 3 times extra warmth than an equivalent PVC cable. This means is that burning polyethylene will not only generate virtually three occasions more warmth but in addition consume nearly 3 instances more oxygen and produce significantly more carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this example is at best alarming!

pressure gauge 4 นิ้ว shown in the table above indicate the amount of warmth which shall be generated by burning 1kg of the widespread cable insulations tabled. Certainly this warmth will accelerate the burning of other adjacent supplies and should assist spread the hearth in a building but importantly, so as to generate the warmth power, oxygen needs to be consumed. The larger the heat of combustion the extra oxygen is needed, so by choosing insulations with high gasoline elements is including significantly to a minimum of four of the primary risks of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it is best to put in polymeric cables inside metal conduits. This will certainly help flame spread and minimize smoke as a end result of inside the conduit oxygen is restricted; nevertheless this is not a solution. As stated previously, many of the gasses from the decomposing polymeric insulations contained in the conduits are extremely flammable and toxic. These gases will migrate along the conduits to junction packing containers, switch panels, distribution boards, motor management facilities, lamps, switches, and so on. On getting into the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, switch or relay causing the hearth to unfold to a different location.
Conclusion

The reputation of “Halogen Free” while ignoring the other poisonous parts of fireplace is a transparent admission we do not understand the subject nicely nor can we easily outline the dangers of combined toxic parts or human physiological response to them. It is necessary nonetheless, that we don’t proceed to design with only half an understanding of the problem. While no excellent answer exists for organic based mostly cables, we will definitely decrease these critically necessary effects of fire risk:
One option maybe to choose cable insulations and jacket supplies which are halogen free and have a low fuel element, then set up them in metal conduit or possibly the American strategy is best: to use extremely halogenated insulations so that in case of fireplace any flame spread is minimized.
For most energy, control, communication and data circuits there is one complete solution out there for all the problems raised in this paper. It is an answer which has been used reliably for over eighty years. MICC cables can provide a total and complete reply to all the issues related to the fireplace safety of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make positive the cable is successfully fireplace proof. MICC cables don’t have any natural content material so simply can not propagate flame or generate any smoke. The zero gasoline load ensures no heat is added and no oxygen is consumed.
Being inorganic MICC cables can’t generate any halogen or toxic gasses at all together with CO.
Unfortunately many frequent cable fire check methods used right now may inadvertently mislead people into believing the polymeric versatile cable products they purchase and use will carry out as expected in all fireplace situations. As outlined on this paper, sadly this is most likely not appropriate.
For more information, go to www.temperature-house.com

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