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Often the best flame retardant cables are halogenated as a end result of both the insulation and outer Jacket are flame retardant however once we want Halogen Free cables we find it is typically only the outer jacket which is flame retardant and the internal insulation is not.
This has significance as a outcome of whereas cables with a flame retardant outer jacket will often cross flame retardance tests with external flame, the same cables when subjected to high overload or prolonged short circuits have proved in university exams to be highly flammable and may even start a hearth. This effect is known and published (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s perhaps stunning that there are no widespread test protocols for this seemingly common event and one cited by both authorities and media as explanation for constructing fires.
Further, in Flame Retardant check methods such as IEC60332 elements 1 & 3 which employ an exterior flame supply, the cable samples aren’t pre-conditioned to regular operating temperature however tested at room temperature. This oversight is important particularly for energy 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) will be considerably affected by its beginning temperature i.e.: The hotter the cable is, the extra simply it’s going to propagate fire.
It would appear that a need exists to re-evaluate present cable flame retardance check strategies as these are generally understood by consultants and customers alike to provide a reliable indication of a cables ability to retard the propagation of fire.
If we can’t trust the Standards what will we do?
In the USA many building standards do not require halogen free cables. Certainly this is not because Americans aren’t correctly informed of the dangers; quite the approach taken is that: “It is healthier to have extremely flame retardant cables which do not propagate hearth than minimally flame retardant cables which can unfold a fire” – (a small fire with some halogen could additionally be higher than a large hearth with out halogens). One of the most effective methods to make a cable insulation and cable jacket highly flame retardant is by using halogens.
Europe and many nations around the world adopt a special mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the truth is somewhat totally different: Flame propagation tests for cables as adopted in UK and Europe can arguably be stated to be less stringent than a number of the flame propagation exams for cables in USA resulting in the conclusion that widespread tests in UK and Europe could merely be exams the cables can move somewhat than exams the cables should pass.
For most versatile polymeric cables the selection remains today between high flame propagation efficiency with halogens or decreased flame propagation performance without halogens.
Enclosing cables in metal conduit will reduce propagation at the point of fireside but hydrocarbon based combustion gasses from decomposing polymers are probably propagate through the conduits to switchboards, distribution boards and junction packing containers in other components of the constructing. Any spark such as the opening or closing of circuit breakers, or contactors is prone to ignite the combustible gasses resulting in explosion and spreading the fireplace to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide an answer, there may be usually no singe perfect reply for every set up so designers need to judge the required efficiency on a “project-by-project” foundation to resolve which expertise is perfect.
The major importance of fireside load
Inside all buildings and initiatives electric cables provide the connectivity which keeps lights on, air-conditioning working and the lifts operating. It powers computers, workplace equipment and provides the connection for our phone and computer systems. Even our cell phones need to attach with wireless or GSM antennas that are linked to the telecom network by fiber optic or copper cables. Cables guarantee our safety by connecting
hearth alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, fireplace sprinkler pumps, smoke and warmth detectors, and so many different features of a contemporary Building Management System.
Where public safety is essential we regularly request cables to have added safety features similar to flame retardance to ensure the cables do not simply unfold fireplace, circuit integrity during fire in order that important fire-fighting and life security gear keep working. Sometimes we might acknowledge that the combustion of electrical cables produces smoke and this can 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 install will be safer
Because cables are put in by many various trades for different functions and are principally hidden or embedded in our constructions, what is commonly not realized is that the numerous miles of cables and tons of plastic polymers which make up the cables can symbolize one of the biggest fireplace hundreds within the building. This level is actually value pondering extra 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 supplies aren’t typically flame retardant and naturally have a excessive fireplace load. Cable producers make them flame retardant by including compounds and chemicals. Certainly this improves the volatility of burning however the fuel content of the base polymers remains.
Tables 1 and 2 above compare the hearth load in MJ/Kg for widespread cable insulating materials against some common fuels. The Heat Release Rate and volatility in air for these materials will differ but the fuel added to a fireplace per kilogram and the consequential volume 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 appreciable. This is particularly essential in initiatives with lengthy egress instances like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When considering hearth safety we should first understand the most important factors. Fire experts tell us most fireplace related deaths in buildings are brought on by smoke inhalation, temperature rise and oxygen depletion or by trauma attributable to leaping in trying to flee these results.
The first and most necessary side of smoke is how a lot smoke? Typically the larger the hearth the more smoke is generated so something we are ready to do to reduce the spread of fireplace may also correspondingly cut back the quantity of smoke.
Smoke will contain particulates of carbon, ash and other solids, liquids and gasses, many are toxic and combustible. In explicit, fires in confined areas like buildings, tunnels and underground environments trigger oxygen ranges to drop, this contributes to incomplete burning and smoldering which produces increased amounts of smoke and poisonous byproducts together with CO and CO2. Presence of halogenated supplies will launch poisonous Halides like Hydrogen Chloride along with many other toxic and flammable gasses in the smoke.
For this purpose frequent smoke tests conducted on cable insulation materials in giant three meter3 chambers with loads of air can provide misleading smoke figures as a end result of complete burning will usually release considerably much less smoke than partial incomplete burning which is likely in follow. Simply specifying IEC 61034 with an outlined obscuration worth then considering this will provide a low smoke setting during hearth might sadly be little of help for the people really involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and different nations undertake the concept of halogen free materials without properly addressing the topic of toxicity. Halogens released during combustion are extremely toxic however so too is carbon monoxide and this is not a halogen gasoline. It is common to call for halogen free cables and then allow the utilization of Polyethylene because it is halogen free. Burning Polyethylene (which may be seen from the table above has the best MJ gas load per Kg of all insulations) will generate nearly three times more warmth than an equivalent PVC cable. This means is that burning polyethylene will not solely generate nearly 3 instances more warmth but additionally eat virtually 3 times extra oxygen and produce significantly more carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this case is at best alarming!
The gas components proven within the desk above indicate the quantity of heat which might be generated by burning 1kg of the frequent cable insulations tabled. Certainly this warmth will speed up the burning of other adjacent supplies and will assist unfold the hearth in a building but importantly, so as to generate the warmth vitality, oxygen needs to be consumed. The greater the warmth of combustion the extra oxygen is required, so by selecting insulations with excessive gas components is including considerably to no less than four of the first risks 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 spread and reduce smoke as a outcome of inside the conduit oxygen is limited; however this isn’t an answer. As stated beforehand, many of the gasses from the decomposing polymeric insulations inside the conduits are highly flammable and toxic. These gases will migrate alongside the conduits to junction boxes, switch panels, distribution boards, motor control centers, lamps, switches, etc. 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 causing the fire to spread to another location.
The recognition of “Halogen Free” while ignoring the opposite poisonous components of fire is a transparent admission we do not perceive the subject well nor can we easily define the dangers of combined toxic elements or human physiological response to them. It is necessary nevertheless, that we don’t proceed to design with solely half an understanding of the problem. While no good solution exists for organic based cables, we will certainly minimize these critically important results of fire danger:
One possibility maybe to choose cable insulations and jacket materials that are halogen free and have a low gasoline element, then set up them in steel conduit or maybe the American method is healthier: to use extremely halogenated insulations in order that in case of fire any flame spread is minimized.
For เกจแรงดัน , control, communication and data circuits there could be one full resolution obtainable 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 security of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively fireplace proof. MICC cables don’t have any organic content material so simply can not propagate flame or generate any smoke. The zero fuel load ensures no warmth is added and no oxygen is consumed.
Being inorganic MICC cables can’t generate any halogen or toxic gasses in any respect including CO.
Unfortunately many common cable fireplace take a look at methods used right now might inadvertently mislead individuals into believing the polymeric versatile cable merchandise they buy and use will perform as expected in all hearth situations. As outlined on this paper, sadly this is probably not appropriate.
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