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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 find it is typically solely the outer jacket which is flame retardant and the inner insulation isn’t.
This has significance as a outcome of whereas cables with a flame retardant outer jacket will often move flame retardance checks with exterior flame, the identical cables when subjected to excessive overload or prolonged short circuits have proved in college checks to be extremely flammable and can even begin a fire. This effect is known and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is perhaps shocking that there are not any widespread take a look at protocols for this seemingly frequent occasion and one cited by both authorities and media as reason for building fires.
Further, in Flame Retardant test strategies corresponding to IEC60332 parts 1 & 3 which employ an exterior flame supply, the cable samples are not pre-conditioned to normal working temperature but examined at room temperature. This oversight is important especially for power circuits because the temperature index of the cable (the temperature at which the cable materials will self-support combustion in normal air) shall be significantly affected by its beginning temperature i.e.: The hotter the cable is, the extra simply it’s going to propagate fireplace.
ราคาเพรสเชอร์เกจ would appear that a want exists to re-evaluate current cable flame retardance test strategies as these are generally understood by consultants and customers alike to supply a dependable indication of a cables ability to retard the propagation of fireplace.
If we can’t trust the Standards what do we do?
In the USA many constructing standards do not require halogen free cables. Certainly this is not as a outcome of Americans aren’t properly informed of the risks; somewhat the approach taken is that: “It is better to have highly flame retardant cables which do not propagate fire than minimally flame retardant cables which may spread a fire” – (a small fire with some halogen may be better than a big fire without halogens). One of one of the best methods to make a cable insulation and cable jacket extremely flame retardant is by using halogens.
Europe and a lot of countries around the world undertake a unique mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is quite different: Flame propagation checks for cables as adopted in UK and Europe can arguably be said to be less stringent than some of the flame propagation checks for cables in USA leading to the conclusion that widespread exams in UK and Europe might merely be tests the cables can move somewhat than tests the cables ought to pass.
Conclusion
For most versatile polymeric cables the choice stays at present between excessive flame propagation performance with halogens or reduced flame propagation efficiency with out halogens.
Enclosing cables in steel conduit will reduce propagation on the point of fire however hydrocarbon based combustion gasses from decomposing polymers are probably propagate through the conduits to switchboards, distribution boards and junction packing containers in different parts of the building. Any spark such because the opening or closing of circuit breakers, or contactors is likely to ignite the flamable gasses leading to explosion and spreading the fireplace to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would offer a solution, there may be often no singe excellent reply for each set up so designers want to evaluate the required performance on a “project-by-project” basis to determine which know-how is perfect.
The main significance of fire load
Inside all buildings and initiatives electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts working. It powers computers, office equipment and offers the connection for our phone and computers. Even our cellphones want to attach with wireless or GSM antennas which are linked to the telecom network by fiber optic or copper cables. Cables ensure our safety by connecting
hearth alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, fireplace sprinkler pumps, smoke and heat detectors, and so many different options of a contemporary Building Management System.
Where public security is essential we often request cables to have added safety features such as flame retardance to make sure the cables don’t simply spread fire, circuit integrity during fire so that important fire-fighting and life security equipment keep working. Sometimes we may recognize that the combustion of electrical cables produces smoke and this could 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 purchase and set up might be safer
Because cables are put in by many different trades for different functions and are principally hidden or embedded in our constructions, what is commonly not realized is that the various miles of cables and tons of plastic polymers which make up the cables can represent one of many largest fire hundreds within the constructing. This point is definitely price pondering extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are principally primarily based on hydrocarbon polymers. These base materials usually are not usually flame retardant and naturally have a high fire load. Cable producers make them flame retardant by including compounds and chemicals. Certainly this improves the volatility of burning but the fuel content of the bottom polymers remains.
Tables 1 and a pair of above compare the hearth load in MJ/Kg for common cable insulating supplies in opposition to some common fuels. The Heat Release Rate and volatility in air for these supplies will differ but the gas 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 put in in our buildings and the associated fire load of the insulations is considerable. This is particularly important in tasks with long egress instances like high rise, public buildings, tunnels and underground environments, airports, hospitals and so on.
When considering hearth safety we must first perceive an important elements. Fire consultants tell us most fire related deaths in buildings are caused by 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 aspect of smoke is how a lot smoke? Typically the larger the fire the more smoke is generated so something we will do to reduce the unfold of fireplace may also correspondingly cut back the quantity of smoke.
Smoke will comprise particulates of carbon, ash and different solids, liquids and gasses, many are poisonous and combustible. 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 amounts of smoke and poisonous byproducts including CO and CO2. Presence of halogenated supplies will launch poisonous Halides like Hydrogen Chloride along with many different poisonous and flammable gasses within the smoke.
For this reason frequent smoke checks conducted on cable insulation supplies in large 3 meter3 chambers with loads of air can present deceptive smoke figures as a outcome of complete burning will often release considerably less smoke than partial incomplete burning which is likely in apply. Simply specifying IEC 61034 with a defined obscuration worth then pondering this can provide a low smoke environment throughout hearth could unfortunately be little of help for the folks really involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other countries adopt the concept of halogen free materials with out properly addressing the subject of toxicity. Halogens released throughout combustion are extraordinarily toxic however so too is carbon monoxide and this isn’t a halogen fuel. It is common to name for halogen free cables and then permit using Polyethylene because it’s halogen free. Burning Polyethylene (which may be seen from the table above has the very best MJ gas load per Kg of all insulations) will generate almost three times extra heat than an equivalent PVC cable. This means is that burning polyethylene will not solely generate nearly three instances more heat but in addition consume virtually 3 occasions extra oxygen and produce significantly more carbon monoxide. Given carbon monoxide is answerable for most toxicity deaths in fires this example is at best alarming!
The gas components proven within the desk above point out the amount of heat which shall be generated by burning 1kg of the frequent cable insulations tabled. Certainly this warmth will speed up the burning of different adjoining supplies and will assist spread the fire in a building but importantly, in order to generate the heat power, oxygen needs to be consumed. The higher the heat of combustion the extra oxygen is required, so by selecting insulations with high gas parts is adding significantly to no less than 4 of the primary dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to install polymeric cables inside steel conduits. This will certainly assist flame unfold and reduce smoke as a outcome of inside the conduit oxygen is restricted; however this isn’t a solution. As said beforehand, many of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and poisonous. These gases will migrate along the conduits to junction packing containers, change panels, distribution boards, motor control facilities, lamps, switches, and so forth. On coming into the gases can ignite or explode with any arcing such because the make/break of a circuit breaker, contactor, change or relay inflicting the fire to spread to another location.
Conclusion
The recognition of “Halogen Free” while ignoring the other poisonous elements of fireside is a transparent admission we do not perceive the subject properly nor can we simply define the risks of combined toxic parts or human physiological response to them. It is necessary nevertheless, that we do not continue to design with solely half an understanding of the issue. While no excellent resolution exists for organic based mostly cables, we can definitely decrease these critically essential results of fire threat:
One possibility possibly to choose cable insulations and jacket supplies that are halogen free and have a low gas element, then install them in steel conduit or perhaps the American method is best: to make use of highly halogenated insulations so that in case of fireside any flame unfold is minimized.
For most power, control, communication and data circuits there is one full resolution obtainable for all the problems raised in this paper. It is an answer which has been used reliably for over 80 years. MICC cables can present a complete and full reply to all the problems associated with the fire security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is successfully fireplace proof. MICC cables have no natural content so simply cannot propagate flame or generate any smoke. The zero gas load ensures no heat is added and no oxygen is consumed.
Being inorganic MICC cables cannot generate any halogen or toxic gasses at all together with CO.
Unfortunately many common cable fireplace test strategies used right now might inadvertently mislead people into believing the polymeric flexible cable merchandise they purchase and use will perform as anticipated in all hearth conditions. As outlined on this paper, sadly this may not be right.
For more information, go to www.temperature-house.com
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