Fire Performance of Electric Cables

Often the best flame retardant cables are halogenated as a end result of each the insulation and outer Jacket are flame retardant but once we want Halogen Free cables we discover it’s usually solely the outer jacket which is flame retardant and the internal insulation isn’t.
This has significance because whereas cables with a flame retardant outer jacket will often move flame retardance checks with exterior flame, the identical cables when subjected to high overload or extended brief circuits have proved in university tests to be extremely flammable and can even start a fire. This effect is understood and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s perhaps shocking that there aren’t any frequent test protocols for this seemingly frequent occasion and one cited by both authorities and media as explanation for building fires.
Further, in Flame Retardant take a look at strategies corresponding to IEC60332 parts 1 & 3 which employ an external flame source, the cable samples aren’t pre-conditioned to regular working temperature but examined at room temperature. This oversight is essential especially for power circuits because the temperature index of the cable (the temperature at which the cable materials will self-support combustion in regular air) shall be considerably affected by its beginning temperature i.e.: The hotter the cable is, the more simply it will propagate fire.
It would seem that a need exists to re-evaluate current cable flame retardance test methods as these are commonly understood by consultants and shoppers alike to provide a dependable indication of a cables capacity to retard the propagation of fireplace.
If we can’t belief the Standards what do we do?
In the USA many constructing standards don’t require halogen free cables. Certainly this isn’t as a result of Americans aren’t properly knowledgeable of the dangers; somewhat the strategy taken is that: “It is healthier to have extremely flame retardant cables which do not propagate hearth than minimally flame retardant cables which can spread a fire” – (a small fire with some halogen could also be better than a large fireplace without halogens). One of the best methods to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and many countries around the globe undertake a special mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is quite totally different: Flame propagation checks 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 widespread tests in UK and Europe might simply be checks the cables can move quite than checks the cables should cross.
For most flexible polymeric cables the choice remains today between excessive flame propagation performance with halogens or decreased flame propagation performance with out halogens.
Enclosing cables in metal conduit will scale back propagation at the level of fireplace however hydrocarbon based mostly combustion gasses from decomposing polymers are likely propagate by way of the conduits to switchboards, distribution boards and junction bins in different components of the building. Any spark such because the opening or closing of circuit breakers, or contactors is more likely to ignite the combustible gasses leading to explosion and spreading the fire to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would supply an answer, there is typically no singe perfect reply for each set up so designers need to evaluate the required efficiency on a “project-by-project” foundation to resolve which know-how is perfect.
pressure gauge ลม of fire load
Inside all buildings and tasks electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts operating. It powers computers, workplace tools and supplies the connection for our phone and computer systems. Even our mobile phones need to attach with wi-fi or GSM antennas which are connected to the telecom community by fiber optic or copper cables. Cables guarantee our safety by connecting
fire alarms, emergency voice communication, CCTV, smoke shutters, air pressurization followers, emergency lighting, fire sprinkler pumps, smoke and warmth detectors, and so many other options of a modern Building Management System.
Where public security is essential we often request cables to have added safety features corresponding to flame retardance to make sure the cables don’t simply unfold fire, circuit integrity during hearth so that important fire-fighting and life security equipment maintain 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 predict that by requesting these particular properties the cables we purchase and install might be safer
Because cables are installed by many various trades for various applications and are largely hidden or embedded in our constructions, what is often not realized is that the numerous miles of cables and tons of plastic polymers which make up the cables can characterize one of the greatest fire hundreds within the building. This point is definitely price considering more 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 usually 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 material of the base polymers stays.
Tables 1 and 2 above examine the fire load in MJ/Kg for frequent cable insulating supplies in opposition to some frequent fuels. The Heat Release Rate and volatility in air for these materials will differ however the gas 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 put in in our buildings and the associated fire load of the insulations is appreciable. This is particularly necessary in initiatives with lengthy egress times like excessive rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When considering hearth security we should first understand the most important factors. Fire specialists tell us most hearth associated deaths in buildings are brought on by smoke inhalation, temperature rise and oxygen depletion or by trauma brought on by leaping in trying to flee these effects.
The first and most essential side of smoke is how much smoke? Typically the larger the hearth the more smoke is generated so anything we can do to cut back the spread of fireside may even correspondingly cut 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 elevated amounts of smoke and poisonous byproducts together with CO and CO2. Presence of halogenated supplies will launch poisonous Halides like Hydrogen Chloride together with many other poisonous and flammable gasses within the smoke.
For this cause common smoke tests conducted on cable insulation supplies in giant three meter3 chambers with plenty of air can provide misleading smoke figures as a outcome of complete burning will usually launch significantly much less smoke than partial incomplete burning which is probably going in apply. Simply specifying IEC 61034 with an outlined obscuration value then considering this will provide a low smoke setting during fire might unfortunately be little of help for the folks actually involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and different nations adopt the idea of halogen free supplies with out correctly addressing the subject of toxicity. Halogens released during combustion are extraordinarily toxic however so too is carbon monoxide and this is not a halogen gas. It is common to name for halogen free cables and then enable the usage of Polyethylene as a result of it’s halogen free. Burning Polyethylene (which can be seen from the desk above has the highest MJ gas load per Kg of all insulations) will generate virtually three instances more warmth than an equivalent PVC cable. This means is that burning polyethylene is not going to only generate nearly 3 occasions more heat but in addition eat almost three instances more oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this example is at best alarming!
The fuel parts proven in the desk above indicate the quantity of heat which might be generated by burning 1kg of the common cable insulations tabled. Certainly this warmth will speed up the burning of other adjoining materials and should assist spread the fireplace in a constructing however importantly, so as to generate the heat vitality, oxygen must be consumed. The larger the warmth of combustion the extra oxygen is needed, so by choosing insulations with high gasoline components is including considerably to at least 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 metallic conduits. This will certainly help flame spread and minimize smoke as a outcome of contained in the conduit oxygen is limited; nevertheless this is not an answer. As stated beforehand, lots of the gasses from the decomposing polymeric insulations contained in the conduits are highly flammable and toxic. These gases will migrate alongside the conduits to junction boxes, change panels, distribution boards, motor management facilities, lamps, switches, and so forth. On getting into the gases can ignite or explode with any arcing such because the make/break of a circuit breaker, contactor, switch or relay causing the fireplace to unfold to a different location.
The recognition of “Halogen Free” whereas ignoring the other toxic parts of fireside is a transparent admission we do not understand the topic properly nor can we simply outline the risks of combined toxic components or human physiological response to them. It is important nevertheless, that we do not proceed to design with solely half an understanding of the problem. While no good answer exists for organic based mostly cables, we can definitely decrease these critically important results of fire danger:
One possibility maybe to decide on cable insulations and jacket materials which are halogen free and have a low gas factor, then set up them in metal conduit or maybe the American approach is best: to use highly halogenated insulations in order that in case of fireplace any flame unfold is minimized.
For most energy, control, communication and information circuits there is one complete answer available for all the issues raised in this paper. It is an answer which has been used reliably for over eighty years. MICC cables can provide a complete and full reply to all the issues related to the fire security of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is successfully fire proof. MICC cables don’t have any organic content material so merely can’t propagate flame or generate any smoke. The zero fuel load ensures no warmth is added and no oxygen is consumed.
Being inorganic MICC cables cannot generate any halogen or toxic gasses in any respect together with CO.
Unfortunately many frequent cable fireplace take a look at methods used at present could inadvertently mislead folks into believing the polymeric flexible cable merchandise they buy and use will carry out as expected in all hearth situations. As outlined on this paper, sadly this is probably not right.
For more information, go to

Scroll to Top