Often the best flame retardant cables are halogenated because each the insulation and outer Jacket are flame retardant but after we want Halogen Free cables we find it is typically only the outer jacket which is flame retardant and the internal insulation isn’t.
This has significance as a outcome of whereas cables with a flame retardant outer jacket will usually move flame retardance tests with external flame, the identical cables when subjected to excessive overload or extended short circuits have proved in college tests to be extremely flammable and may even begin a fireplace. This effect is understood and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s perhaps stunning that there are not any common test protocols for this seemingly frequent occasion and one cited by both authorities and media as cause of building fires.
Further, in Flame Retardant take a look at strategies similar to IEC60332 elements 1 & three which employ an exterior flame supply, the cable samples are not pre-conditioned to regular working temperature but tested at room temperature. This oversight is necessary particularly for power circuits as a outcome of 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 starting temperature i.e.: The hotter the cable is, the more easily it will propagate hearth.
It would appear that a want exists to re-evaluate present cable flame retardance check methods as these are commonly understood by consultants and customers alike to provide a dependable indication of a cables ability to retard the propagation of fireside.
If we can’t trust the Standards what will we do?
In the USA many constructing standards don’t require halogen free cables. Certainly this isn’t because Americans are not correctly knowledgeable of the dangers; quite the method taken is that: “It is healthier to have highly flame retardant cables which do not propagate hearth than minimally flame retardant cables which can spread a fire” – (a small hearth with some halogen may be higher than a large hearth without halogens). One of the most effective ways to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and tons of countries all over the world undertake a different mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the reality is somewhat totally different: Flame propagation checks for cables as adopted in UK and Europe can arguably be stated to be less stringent than a few of the flame propagation checks for cables in USA leading to the conclusion that common exams in UK and Europe may merely be checks the cables can move rather than checks the cables should pass.
Conclusion
For most flexible polymeric cables the choice remains today between high flame propagation efficiency with halogens or lowered flame propagation efficiency with out halogens.
Enclosing cables in metal conduit will reduce propagation at the point of fire but hydrocarbon primarily based combustion gasses from decomposing polymers are probably propagate via the conduits to switchboards, distribution boards and junction bins in other parts of the constructing. Any spark such because the opening or closing of circuit breakers, or contactors is likely to ignite the flamable gasses resulting in explosion and spreading the hearth to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would supply a solution, there might be usually no singe perfect reply for every installation so designers want to evaluate the required performance on a “project-by-project” basis to resolve which expertise is perfect.
The primary significance of fire load
Inside all buildings and projects electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts running. It powers computer systems, workplace gear and provides the connection for our phone and computers. Even our mobile phones need to attach with wi-fi or GSM antennas which are linked to the telecom community by fiber optic or copper cables. Cables ensure our safety by connecting
fireplace alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, fire sprinkler pumps, smoke and heat detectors, and so many different options of a modern Building Management System.
Where public safety is necessary we regularly request cables to have added safety features such as flame retardance to make sure the cables do not easily unfold fireplace, circuit integrity during fireplace so that essential fire-fighting and life security tools keep working. Sometimes we could recognize that the combustion of electric cables produces smoke and this can be poisonous so we name 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 set up shall be safer
Because cables are put in by many different trades for different purposes and are principally hidden or embedded in our constructions, what is usually not realized is that the many miles of cables and tons of plastic polymers which make up the cables can represent one of the greatest fire loads in the building. This level is definitely price thinking extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are largely primarily based on hydrocarbon polymers. These base supplies usually are not generally flame retardant and naturally have a excessive hearth load. Cable manufacturers make them flame retardant by including compounds and chemicals. Certainly this improves the volatility of burning however the fuel content material of the base polymers stays.
Tables 1 and a pair of above compare the fireplace load in MJ/Kg for widespread cable insulating materials in opposition to some widespread fuels. The Heat Release Rate and volatility in air for these supplies will differ however the gas 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 installed in our buildings and the related hearth load of the insulations is appreciable. This is particularly necessary in tasks with lengthy egress occasions like high rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When contemplating fireplace safety we should first perceive crucial components. Fire consultants tell us most hearth associated deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma brought on by jumping in making an attempt to escape these results.
Smoke
The first and most important side of smoke is how a lot smoke? Typically the larger the fireplace the more smoke is generated so anything we are in a position to do to minimize back the spread of fireplace will also correspondingly cut back the amount of smoke.
Smoke will contain particulates of carbon, ash and different solids, liquids and gasses, many are toxic and flamable. In explicit, fires in confined areas like buildings, tunnels and underground environments trigger oxygen levels to drop, this contributes to incomplete burning and smoldering which produces elevated quantities of smoke and poisonous byproducts including CO and CO2. Presence of halogenated materials will release poisonous Halides like Hydrogen Chloride together with many different poisonous and flammable gasses within the smoke.
For this purpose frequent smoke exams conducted on cable insulation materials in massive three meter3 chambers with loads of air can provide misleading smoke figures as a result of complete burning will typically launch significantly less smoke than partial incomplete burning which is likely in follow. Simply specifying IEC 61034 with an outlined obscuration worth then thinking this can present a low smoke surroundings during fireplace may unfortunately be little of assist for the individuals truly concerned.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and other countries undertake the idea of halogen free supplies with out properly addressing the subject of toxicity. Halogens launched during combustion are extremely toxic however so too is carbon monoxide and this is not a halogen gas. It is widespread to name for halogen free cables after which enable using Polyethylene as a outcome of it’s halogen free. Burning Polyethylene (which can be seen from the table above has the best MJ gasoline load per Kg of all insulations) will generate virtually three occasions extra heat than an equal PVC cable. This means is that burning polyethylene is not going to only generate virtually three instances extra warmth but in addition consume almost 3 occasions extra oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this situation is at best alarming!
The gas parts shown in the table above point out 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 adjoining supplies and should help spread the fireplace in a building but importantly, in order to generate the heat energy, oxygen needs to be consumed. The greater the warmth of combustion the extra oxygen is required, so by selecting insulations with high gasoline parts is including significantly to no less than four of the primary risks of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to put in polymeric cables inside steel conduits. This will certainly assist flame unfold and decrease smoke as a outcome of inside the conduit oxygen is limited; however this isn’t a solution. As said previously, lots 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 packing containers, switch panels, distribution boards, motor control facilities, lamps, switches, etc. On getting into the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, switch or relay inflicting the hearth to unfold to another location.
เกจวัดแรงดัน300psi of “Halogen Free” while ignoring the opposite toxic components of fireside is a clear admission we don’t perceive the topic nicely nor can we simply outline the hazards of combined toxic components or human physiological response to them. It is essential however, that we don’t proceed to design with only half an understanding of the issue. While no good solution exists for natural based cables, we are able to certainly decrease these critically essential effects of fire threat:
One possibility maybe to decide on cable insulations and jacket materials which are halogen free and have a low fuel element, then install them in steel conduit or perhaps the American approach is healthier: to use highly halogenated insulations in order that in case of fireside any flame unfold is minimized.
For most power, management, communication and information circuits there’s one full solution out there for all the problems raised in this paper. It is a solution which has been used reliably for over 80 years. MICC cables can provide a total and complete answer to all the problems related to the fire security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively fire proof. MICC cables have no organic content material so simply can not propagate flame or generate any smoke. The zero gasoline load ensures no warmth is added and no oxygen is consumed.
Being inorganic MICC cables can not generate any halogen or toxic gasses in any respect including CO.
Unfortunately many widespread cable fire check methods used today might inadvertently mislead individuals into believing the polymeric versatile cable merchandise they purchase and use will carry out as expected in all fire conditions. As outlined in this paper, sadly this is probably not correct.
For extra info, go to www.temperature-house.com
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