Fire Performance of Electric Cables

Often one of the best flame retardant cables are halogenated as a result of each the insulation and outer Jacket are flame retardant however when we need Halogen Free cables we discover it’s usually solely the outer jacket which is flame retardant and the inside insulation is not.
This has significance because whereas cables with a flame retardant outer jacket will usually move flame retardance tests with exterior flame, the identical cables when subjected to excessive overload or extended brief circuits have proved in college exams to be highly flammable and may 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 aren’t any widespread check protocols for this seemingly widespread occasion and one cited by both authorities and media as explanation for constructing fires.
Further, in Flame Retardant check strategies such as IEC60332 elements 1 & three which make use of an external flame supply, the cable samples are not pre-conditioned to regular working temperature however tested at room temperature. This oversight is important especially for energy circuits because the temperature index of the cable (the temperature at which the cable materials will self-support combustion in regular air) will be considerably affected by its starting temperature i.e.: The hotter the cable is, the extra simply it’s going to propagate fire.
It would appear that a want exists to re-evaluate present cable flame retardance take a look at methods as these are generally understood by consultants and shoppers alike to provide a dependable indication of a cables capacity to retard the propagation of fire.
If we can’t belief the Standards what do we do?
In the USA many constructing requirements don’t require halogen free cables. Certainly this is not as a end result of Americans aren’t properly informed of the dangers; rather the method taken is that: “It is healthier to have highly flame retardant cables which don’t propagate fireplace than minimally flame retardant cables which may unfold a fire” – (a small fireplace with some halogen could additionally be better than a large fire without halogens). เกวัดแรงดันน้ำ of one of the best methods to make a cable insulation and cable jacket highly flame retardant is through the use of halogens.
Europe and a lot of international locations all over the world adopt a different mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is rather totally different: Flame propagation tests for cables as adopted in UK and Europe can arguably be mentioned to be less stringent than some of the flame propagation exams for cables in USA resulting in the conclusion that common tests in UK and Europe may merely be tests the cables can pass quite than exams the cables ought to cross.
For most flexible polymeric cables the choice remains right now between high flame propagation efficiency with halogens or lowered flame propagation efficiency without halogens.
Enclosing cables in steel conduit will reduce propagation at the point of fireplace however hydrocarbon primarily based combustion gasses from decomposing polymers are doubtless propagate by way of the conduits to switchboards, distribution boards and junction boxes in different elements of the building. 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 hearth to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would offer a solution, there’s typically no singe perfect reply for every installation so designers need to gauge the required efficiency on a “project-by-project” basis to resolve which know-how is optimal.
The major significance of fire load
Inside all buildings and projects electric cables provide the connectivity which keeps lights on, air-conditioning working and the lifts operating. It powers computers, office gear and supplies the connection for our phone and computers. Even our mobile phones want to connect with wi-fi or GSM antennas that are related 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, hearth sprinkler pumps, smoke and warmth detectors, and so many different options of a contemporary Building Management System.
Where public safety is essential we often request cables to have added safety options corresponding to flame retardance to make sure the cables do not simply unfold hearth, circuit integrity during fire in order that important fire-fighting and life safety equipment keep working. Sometimes we could acknowledge that the combustion of electric 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 special properties the cables we purchase and install shall be safer
Because cables are installed by many alternative trades for different functions and are mostly 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 characterize one of many biggest fireplace hundreds within the constructing. This point is actually worth thinking extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are largely based mostly on hydrocarbon polymers. These base supplies are not typically 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 fuel content of the base polymers stays.
Tables 1 and a pair of above evaluate the fire load in MJ/Kg for frequent cable insulating supplies towards some widespread fuels. The Heat Release Rate and volatility in air for these supplies will differ but the fuel added to a fireplace per kilogram and the consequential quantity of warmth generated and oxygen consumed is relative.
The volume in kilometers and tons of cables installed in our buildings and the associated fire load of the insulations is considerable. This is especially necessary in initiatives with lengthy egress times like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When considering fireplace security we must first perceive an important factors. Fire consultants inform us most fireplace associated deaths in buildings are attributable to 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 much smoke? Typically the bigger the fireplace the more smoke is generated so anything we will do to reduce the unfold of fireplace will also correspondingly reduce the amount of smoke.
Smoke will contain particulates of carbon, ash and other solids, liquids and gasses, many are toxic and combustible. In particular, fires in confined areas like buildings, tunnels and underground environments trigger oxygen levels to drop, this contributes to incomplete burning and smoldering which produces increased amounts of smoke and toxic byproducts including CO and CO2. Presence of halogenated supplies will release poisonous Halides like Hydrogen Chloride along with many other toxic and flammable gasses within the smoke.
For this reason frequent smoke checks carried out on cable insulation supplies in giant three meter3 chambers with plenty of air can provide misleading smoke figures as a end result of full burning will typically launch 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 environment during hearth might sadly be little of assist for the people truly involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and other nations undertake the idea of halogen free materials with out properly addressing the subject of toxicity. Halogens launched throughout combustion are extremely poisonous however so too is carbon monoxide and this isn’t a halogen gasoline. It is frequent to call for halogen free cables after which enable using Polyethylene as a outcome of it’s halogen free. Burning Polyethylene (which could be seen from the desk above has the best MJ gas load per Kg of all insulations) will generate almost 3 times more heat than an equivalent PVC cable. This means is that burning polyethylene won’t solely generate virtually three instances more heat but also eat almost 3 instances more oxygen and produce considerably extra carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this case is at greatest alarming!
The gasoline elements proven in the desk above indicate the amount of warmth which might be generated by burning 1kg of the widespread cable insulations tabled. Certainly this heat will speed up the burning of other adjacent supplies and may help spread the hearth in a building however importantly, to be able to generate the heat energy, oxygen must be consumed. The greater the warmth of combustion the extra oxygen is required, so by selecting insulations with excessive fuel elements is adding significantly to no much less than 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 metallic conduits. This will definitely assist flame unfold and minimize smoke because inside the conduit oxygen is limited; nonetheless this isn’t an answer. As said beforehand, most of the gasses from the decomposing polymeric insulations contained in the conduits are extremely flammable and poisonous. เกจวัดแรงดันแก๊สอาร์กอน will migrate along the conduits to junction boxes, switch panels, distribution boards, motor management centers, lamps, switches, and so forth. On coming into the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, change or relay causing the fireplace to unfold to another location.
The reputation of “Halogen Free” while ignoring the other poisonous elements of fire is a transparent admission we do not perceive the subject nicely nor can we easily define the hazards of combined poisonous elements or human physiological response to them. It is necessary nonetheless, that we do not proceed to design with solely half an understanding of the problem. While no excellent answer exists for natural primarily based cables, we can definitely minimize these critically necessary results of fire threat:
One choice possibly to choose cable insulations and jacket materials which are halogen free and have a low gasoline component, then set up them in steel conduit or possibly the American strategy is best: to use extremely halogenated insulations in order that in case of fire any flame unfold is minimized.
For most energy, control, communication and data circuits there’s one complete answer obtainable for all the issues raised on this paper. It is an answer which has been used reliably for over 80 years. MICC cables can present a total and complete answer to all the problems associated with the fireplace safety of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively hearth proof. MICC cables don’t have any organic content material 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 poisonous gasses at all together with CO.
Unfortunately many frequent cable hearth check strategies used right now may inadvertently mislead people into believing the polymeric flexible cable merchandise they purchase and use will carry out as anticipated in all fireplace conditions. As outlined on this paper, sadly this is most likely not right.
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