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Often the most effective flame retardant cables are halogenated as a end result of each the insulation and outer Jacket are flame retardant but when we need Halogen Free cables we discover it’s typically solely the outer jacket which is flame retardant and the inner insulation isn’t.
This has significance as a outcome of while cables with a flame retardant outer jacket will usually cross flame retardance exams with exterior flame, the identical cables when subjected to high overload or extended brief circuits have proved in university exams to be extremely flammable and may even begin a fire. This effect is known and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s maybe shocking that there aren’t any frequent take a look at protocols for this seemingly frequent event and one cited by both authorities and media as explanation for building fires.
Further, in Flame Retardant take a look at methods corresponding to IEC60332 components 1 & three which employ an external flame supply, the cable samples are not pre-conditioned to normal working temperature but examined at room temperature. This oversight is necessary particularly for power circuits as a result of the temperature index of the cable (the temperature at which the cable material will self-support combustion in normal air) shall be significantly affected by its starting temperature i.e.: The hotter the cable is, the extra easily it’s going to propagate fire.
It would seem that a need exists to re-evaluate present cable flame retardance test strategies as these are generally understood by consultants and shoppers alike to supply a dependable indication of a cables ability to retard the propagation of fire.
If we can’t belief the Standards what will we do?

In the USA many building requirements do not require halogen free cables. Certainly this isn’t as a result of Americans are not properly knowledgeable of the dangers; rather the strategy taken is that: “It is best to have extremely flame retardant cables which do not propagate fire than minimally flame retardant cables which may unfold a fire” – (a small fire with some halogen could also be higher than a large fire without halogens). One of the best methods to make a cable insulation and cable jacket highly flame retardant is by utilizing halogens.
Europe and a lot of nations all over the world undertake a different mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the truth is rather totally different: Flame propagation checks for cables as adopted in UK and Europe can arguably be said to be much less stringent than a variety of the flame propagation tests for cables in USA resulting in the conclusion that common checks in UK and Europe might simply be checks the cables can cross rather than checks the cables should cross.
Conclusion

For most flexible polymeric cables the selection stays today between high flame propagation efficiency with halogens or lowered flame propagation performance without halogens.
Enclosing cables in metal conduit will scale back propagation on the point of fireplace but hydrocarbon primarily based combustion gasses from decomposing polymers are doubtless propagate by way of the conduits to switchboards, distribution boards and junction bins in different parts of the constructing. Any spark such because the opening or closing of circuit breakers, or contactors is likely to ignite the flamable gasses resulting in explosion and spreading the fire to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would supply a solution, there’s typically no singe good reply for every set up so designers need to evaluate the required performance on a “project-by-project” basis to resolve which expertise is perfect.
The major importance of fire load

Inside all buildings and projects electrical cables provide the connectivity which keeps lights on, air-conditioning working and the lifts running. It powers computer systems, workplace tools and supplies the connection for our phone and computers. Even our cellphones need to connect with wireless or GSM antennas which are linked to the telecom network by fiber optic or copper cables. Cables ensure our safety by connecting

fire alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, fire sprinkler pumps, smoke and heat detectors, and so many other options of a contemporary Building Management System.
Where public security is essential we often request cables to have added safety options similar to flame retardance to ensure the cables don’t easily spread fireplace, circuit integrity throughout fireplace so that important fire-fighting and life safety equipment hold working. Sometimes we could recognize that the combustion of electric cables produces smoke and this can be toxic so we name for cables to be Low Smoke and Halogen Free. Logically and intuitively we expect that by requesting these special properties the cables we purchase and install might be safer

Because cables are put in by many different trades for different purposes and are principally hidden or embedded in our constructions, what is often not realized is that the various miles of cables and tons of plastic polymers which make up the cables can represent one of many greatest fireplace hundreds within the constructing. This point is certainly price considering extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are largely based on hydrocarbon polymers. These base materials are not usually flame retardant and naturally have a high fireplace load. Cable producers make them flame retardant by adding compounds and chemical compounds. Certainly this improves the volatility of burning however the gas content of the base polymers stays.
Tables 1 and a couple of above examine the fireplace load in MJ/Kg for common cable insulating materials towards some frequent fuels. The Heat Release Rate and volatility in air for these supplies will differ but the fuel added to a fire per kilogram and the consequential quantity of warmth generated and oxygen consumed is relative.
The quantity in kilometers and tons of cables installed in our buildings and the related fire load of the insulations is considerable. This is especially necessary in tasks with long egress times like high rise, public buildings, tunnels and underground environments, airports, hospitals and so on.
When contemplating hearth safety we should first understand crucial components. Fire consultants tell us most hearth related deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma caused by leaping in making an attempt to escape these effects.
Smoke

The first and most important facet of smoke is how much smoke? Typically the larger the fireplace the extra smoke is generated so something we will do to scale back the spread of fireside will also correspondingly reduce the quantity of smoke.
Smoke will contain particulates of carbon, ash and other solids, liquids and gasses, many are toxic and flamable. In explicit, fires in confined areas like buildings, tunnels and underground environments cause oxygen ranges to drop, this contributes to incomplete burning and smoldering which produces elevated quantities of smoke and poisonous byproducts together with CO and CO2. Presence of halogenated supplies will release toxic Halides like Hydrogen Chloride along with many different toxic and flammable gasses in the smoke.
For this reason frequent smoke exams performed on cable insulation materials in massive three meter3 chambers with plenty of air can provide misleading smoke figures as a outcome of complete burning will usually release considerably much less smoke than partial incomplete burning which is probably going in apply. Simply specifying IEC 61034 with a defined obscuration value then pondering it will provide a low smoke environment during fireplace could unfortunately be little of assist for the individuals really concerned.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise

It is regarding that Europe and other nations undertake the concept of halogen free supplies without correctly addressing the subject of toxicity. Halogens released during combustion are extraordinarily toxic but so too is carbon monoxide and this isn’t a halogen gasoline. It is widespread to name for halogen free cables after which enable the usage of Polyethylene as a outcome of it’s halogen free. Burning Polyethylene (which could be seen from the desk above has the highest MJ gas load per Kg of all insulations) will generate nearly three occasions extra warmth than an equal PVC cable. This means is that burning polyethylene won’t only generate nearly three occasions more heat but also consume virtually 3 instances more oxygen and produce significantly more carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this case is at greatest alarming!

The gasoline elements shown in the desk above point out the amount of warmth which might be generated by burning 1kg of the widespread cable insulations tabled. Certainly this warmth will speed up the burning of different adjacent materials and may assist unfold the fire in a constructing but importantly, so as to generate the warmth vitality, oxygen must be consumed. The greater the warmth of combustion the extra oxygen is required, so by choosing insulations with high gas parts is including significantly to no less than 4 of the first dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to install polymeric cables inside metal conduits. This will definitely help flame unfold and minimize smoke as a end result of contained in the conduit oxygen is proscribed; nonetheless this isn’t an answer. As mentioned beforehand, ไดอะแฟรม ซีล of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and toxic. These gases will migrate along the conduits to junction bins, change panels, distribution boards, motor management facilities, lamps, switches, and so forth. On entering 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 spread to another location.
Conclusion

The reputation of “Halogen Free” whereas ignoring the opposite toxic parts of fireplace is a transparent admission we don’t understand the subject properly nor can we simply outline the risks of combined poisonous parts or human physiological response to them. It is essential nonetheless, that we do not proceed to design with only half an understanding of the issue. While no excellent resolution exists for organic based mostly cables, we are ready to certainly reduce these critically important results of fireside danger:
One option possibly to choose cable insulations and jacket materials that are halogen free and have a low gasoline factor, then set up them in metal conduit or possibly the American strategy is best: to use highly halogenated insulations so that in case of fire any flame spread is minimized.
For most power, management, communication and information circuits there’s one full solution obtainable for all the problems raised on this paper. It is an answer which has been used reliably for over eighty years. MICC cables can present a complete and complete answer to all the problems related to the fire safety of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make certain the cable is successfully hearth proof. MICC cables don’t have any natural content so merely can’t 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 not generate any halogen or poisonous gasses in any respect together with CO.
Unfortunately many common cable hearth test strategies used right now may inadvertently mislead folks into believing the polymeric flexible cable products they purchase and use will carry out as expected in all fire conditions. As outlined on เกจวัดแรงดัน , sadly this is most likely not appropriate.
For more information, go to www.temperature-house.com

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