Often the most effective flame retardant cables are halogenated as a outcome of both the insulation and outer Jacket are flame retardant however after we need Halogen Free cables we find it is typically solely the outer jacket which is flame retardant and the internal insulation just isn’t.
This has significance because whereas cables with a flame retardant outer jacket will often cross flame retardance tests with external flame, the same cables when subjected to excessive overload or prolonged quick circuits have proved in university exams to be extremely flammable and might even begin a hearth. This effect is thought and published (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s perhaps surprising that there aren’t any frequent check protocols for this seemingly widespread occasion and one cited by both authorities and media as cause of constructing fires.
Further, in Flame Retardant test strategies similar to IEC60332 components 1 & 3 which employ an exterior flame source, the cable samples are not pre-conditioned to normal operating temperature however tested at room temperature. This oversight is important particularly for energy circuits as a result of the temperature index of the cable (the temperature at which the cable materials will self-support combustion in regular air) shall be significantly affected by its starting temperature i.e.: The hotter the cable is, the extra simply it’s going to propagate hearth.
It would seem that a need exists to re-evaluate present cable flame retardance test methods as these are generally understood by consultants and consumers alike to supply a reliable indication of a cables capacity to retard the propagation of fire.
If we can’t belief the Standards what will we do?
In the USA many building requirements don’t require halogen free cables. Certainly this is not as a result of Americans usually are not correctly knowledgeable of the risks; somewhat the method taken is that: “It is best to have highly flame retardant cables which don’t propagate hearth than minimally flame retardant cables which may spread a fire” – (a small fire with some halogen could additionally be better than a large fireplace without halogens). One of one of the best methods to make a cable insulation and cable jacket highly flame retardant is by using halogens.
Europe and heaps of countries around the globe undertake a special mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is rather different: Flame propagation checks for cables as adopted in UK and Europe can arguably be stated to be much less stringent than some of the flame propagation checks for cables in USA leading to the conclusion that widespread checks in UK and Europe could simply be tests the cables can cross rather than exams the cables should move.
Conclusion
For most versatile polymeric cables the selection remains right now between high flame propagation efficiency with halogens or lowered flame propagation efficiency with out halogens.
Enclosing cables in metal conduit will scale back propagation on the level of fireplace however hydrocarbon based combustion gasses from decomposing polymers are probably propagate by way of the conduits to switchboards, distribution boards and junction bins in different elements of the constructing. Any spark such because the opening or closing of circuit breakers, or contactors is prone to ignite the flamable gasses leading to explosion and spreading the hearth to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would supply an answer, there may be typically no singe good reply for each installation so designers want to judge the required performance on a “project-by-project” basis to decide which know-how is optimal.
เกจวัดแรงดันsumo of fire load
Inside all buildings and initiatives electric cables provide the connectivity which retains lights on, air-conditioning working and the lifts working. It powers computers, workplace gear and offers the connection for our telephone and computers. Even our cell phones want to attach with wi-fi or GSM antennas that are linked to the telecom network by fiber optic or copper cables. Cables guarantee 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 safety is necessary we often request cables to have added safety features similar to flame retardance to make sure the cables don’t simply unfold hearth, circuit integrity throughout hearth in order that essential fire-fighting and life safety gear hold working. Sometimes we may recognize that the combustion of electric cables produces smoke and this may be poisonous so we call for cables to be Low Smoke and Halogen Free. Logically and intuitively we expect that by requesting these particular properties the cables we buy and install shall be safer
Because cables are put in by many different trades for different applications and are largely 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 symbolize one of many biggest hearth loads in the constructing. This point is actually value considering extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are mostly based on hydrocarbon polymers. These base materials aren’t usually flame retardant and naturally have a high hearth load. Cable producers make them flame retardant by including compounds and chemical compounds. Certainly this improves the volatility of burning however the fuel content material of the bottom polymers stays.
Tables 1 and 2 above examine the fireplace load in MJ/Kg for common cable insulating supplies against some widespread fuels. The Heat Release Rate and volatility in air for these supplies will differ however the gasoline added to a hearth per kilogram and the consequential quantity of warmth generated and oxygen consumed is relative.
The quantity in kilometers and tons of cables put in in our buildings and the associated fireplace load of the insulations is appreciable. This is particularly necessary in projects with long egress instances like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so on.
When considering fireplace safety we must first understand an important factors. Fire experts tell 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 flee these results.
Smoke
The first and most essential side of smoke is how much smoke? Typically the bigger the hearth the more smoke is generated so something we can do to scale back the unfold of fireplace will also correspondingly scale back the amount of smoke.
Smoke will comprise particulates of carbon, ash and other solids, liquids and gasses, many are poisonous and combustible. In specific, 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 amounts of smoke and poisonous byproducts including CO and CO2. Presence of halogenated materials will release toxic Halides like Hydrogen Chloride along with many other toxic and flammable gasses in the smoke.
For this purpose widespread smoke checks conducted on cable insulation materials in giant three meter3 chambers with plenty of air can present misleading smoke figures because complete burning will usually launch significantly much less smoke than partial incomplete burning which is most likely going in apply. Simply specifying IEC 61034 with a defined obscuration value then thinking it will provide a low smoke environment during hearth might sadly be little of assist for the folks really concerned.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other countries adopt the concept of halogen free supplies without properly addressing the topic of toxicity. Halogens released during combustion are extremely poisonous but so too is carbon monoxide and this is not a halogen gas. It is widespread to call for halogen free cables after which allow using Polyethylene as a end result of it is halogen free. Burning Polyethylene (which could be seen from the table above has the very best MJ gas load per Kg of all insulations) will generate nearly three times more heat than an equivalent PVC cable. This means is that burning polyethylene won’t only generate almost 3 occasions more warmth but also eat nearly 3 occasions extra oxygen and produce considerably more carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this example is at finest alarming!
The gasoline parts shown within the desk above indicate the amount of heat which will be generated by burning 1kg of the widespread cable insulations tabled. Certainly this warmth will speed up the burning of different adjacent supplies and should help unfold the fire in a constructing however importantly, to have the ability to generate the warmth vitality, oxygen must be consumed. The higher the heat of combustion the extra oxygen is required, so by choosing insulations with excessive gas components is including considerably to a minimum of four of the primary dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it is best to put in polymeric cables inside steel conduits. This will definitely assist flame spread and reduce smoke as a end result of inside the conduit oxygen is proscribed; nevertheless this isn’t an answer. As said beforehand, lots of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and poisonous. These gases will migrate alongside the conduits to junction bins, swap panels, distribution boards, motor management facilities, lamps, switches, and so on. On entering the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, swap or relay causing the fire to unfold to another location.
Conclusion
The reputation of “Halogen Free” while ignoring the other poisonous components of fireplace is a clear admission we do not understand the topic nicely nor can we simply define the hazards of combined poisonous components or human physiological response to them. It is essential however, that we do not continue to design with only half an understanding of the problem. While no good answer exists for organic based mostly cables, we are ready to actually reduce these critically necessary effects of fireplace danger:
One possibility maybe to choose on cable insulations and jacket materials that are halogen free and have a low gasoline element, then install them in steel conduit or maybe the American strategy is best: to use highly halogenated insulations so that in case of fireside any flame unfold is minimized.
For most energy, management, communication and data circuits there could be one complete solution available for all the problems raised on this paper. It is a solution which has been used reliably for over 80 years. MICC cables can provide a complete and complete answer to all the problems associated with the hearth safety of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is successfully hearth proof. MICC cables have no natural content so merely can not propagate flame or generate any smoke. The zero gas 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 including CO.
Unfortunately many widespread cable hearth test methods used today might inadvertently mislead people into believing the polymeric flexible cable products they purchase and use will perform as anticipated in all hearth situations. As outlined on this paper, sadly this is probably not correct.
For more info, go to www.temperature-house.com
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