Often one of the best flame retardant cables are halogenated as a result of each the insulation and outer Jacket are flame retardant but when we need Halogen Free cables we discover it’s often only the outer jacket which is flame retardant and the inner insulation just isn’t.
This has significance as a result of while cables with a flame retardant outer jacket will typically pass flame retardance tests with exterior flame, the identical cables when subjected to high overload or extended quick circuits have proved in university checks to be extremely flammable and may even start a fire. This effect is thought and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is perhaps shocking that there are no widespread test protocols for this seemingly common event and one cited by both authorities and media as cause of constructing fires.
Further, in Flame Retardant test strategies such as IEC60332 parts 1 & three which employ an exterior flame source, the cable samples usually are not pre-conditioned to normal operating temperature but tested at room temperature. This oversight is essential especially for power circuits as a result of the temperature index of the cable (the temperature at which the cable materials will self-support combustion in regular air) might be considerably affected by its starting temperature i.e.: The hotter the cable is, the more simply it’ll propagate hearth.
It would appear that a want exists to re-evaluate present cable flame retardance check 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 fireplace.
If we can’t trust the Standards what can we do?
In the USA many constructing standards do not require halogen free cables. Certainly this isn’t as a result of Americans aren’t properly informed of the dangers; somewhat the approach taken is that: “It is better to have extremely flame retardant cables which don’t propagate fire than minimally flame retardant cables which may spread a fire” – (a small fireplace with some halogen may be better than a big fireplace without halogens). One of one of the best methods to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and tons of countries around the world undertake a different mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the reality is somewhat totally different: Flame propagation tests for cables as adopted in UK and Europe can arguably be stated to be much less stringent than a number of the flame propagation checks for cables in USA resulting in the conclusion that common exams in UK and Europe may merely be checks the cables can pass quite than tests the cables should pass.
Conclusion
For most versatile polymeric cables the selection remains right now between high flame propagation efficiency with halogens or decreased flame propagation performance without halogens.
Enclosing cables in steel conduit will reduce propagation at the level of fireside but hydrocarbon based combustion gasses from decomposing polymers are likely propagate by way of the conduits to switchboards, distribution boards and junction bins in other elements of the constructing. Any spark such because the opening or closing of circuit breakers, or contactors is more probably to ignite the flamable gasses leading to explosion and spreading the fireplace to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide an answer, there’s often no singe perfect reply for every set up so designers want to gauge the required efficiency on a “project-by-project” basis to determine which expertise is optimal.
The primary importance of fireside load
Inside all buildings and tasks electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts working. It powers computers, workplace gear and supplies the connection for our phone and computers. Even our cellphones want to connect with wireless or GSM antennas that 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, fireplace sprinkler pumps, smoke and warmth detectors, and so many other options of a modern Building Management System.
Where public safety is essential we often request cables to have added security features such as flame retardance to ensure the cables do not easily spread fireplace, circuit integrity during hearth so that important fire-fighting and life safety tools maintain working. Sometimes we may acknowledge that the combustion of electric 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 special properties the cables we buy and install will be safer
Because cables are put in by many various trades for various 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 the greatest fire loads in the constructing. This level is definitely value thinking extra about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are largely based on hydrocarbon polymers. These base supplies usually are not typically flame retardant and naturally have a high fireplace load. Cable producers make them flame retardant by adding compounds and chemicals. Certainly this improves the volatility of burning however the fuel content material of the base polymers stays.
Tables 1 and 2 above evaluate the hearth load in MJ/Kg for frequent cable insulating supplies towards some common fuels. The Heat Release Rate and volatility in air for these supplies will differ however the gasoline 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 hearth load of the insulations is appreciable. This is particularly essential in projects with long egress instances like excessive rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When considering fireplace safety we should first perceive crucial elements. Fire specialists tell us most fireplace associated deaths in buildings are brought on by smoke inhalation, temperature rise and oxygen depletion or by trauma attributable to leaping in attempting to escape these results.
เกจวัดแรงดันแบบแห้ง and most necessary facet of smoke is how a lot smoke? Typically the larger the fire the extra smoke is generated so anything we can do to minimize back the unfold of fireplace will also correspondingly reduce the amount of smoke.
Smoke will include particulates of carbon, ash and different solids, liquids and gasses, many are toxic and combustible. In specific, 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 toxic byproducts including CO and CO2. Presence of halogenated supplies will release poisonous Halides like Hydrogen Chloride together with many other poisonous and flammable gasses in the smoke.
For this cause common smoke checks performed on cable insulation supplies in massive three meter3 chambers with loads of air can provide misleading smoke figures because full burning will typically release significantly much less smoke than partial incomplete burning which is likely in apply. Simply specifying IEC 61034 with a defined obscuration value then pondering it will provide a low smoke environment throughout fire might sadly be little of help for the people really involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other international locations undertake the concept of halogen free materials without correctly addressing the subject of toxicity. Halogens released during combustion are extremely poisonous but so too is carbon monoxide and this isn’t a halogen gas. It is widespread to name for halogen free cables and then enable the usage of Polyethylene as a end result of it is halogen free. Burning Polyethylene (which can be seen from the desk above has the very best MJ gas load per Kg of all insulations) will generate virtually 3 times more heat than an equal PVC cable. This means is that burning polyethylene will not only generate virtually 3 times more warmth but in addition consume nearly three times more oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this example is at finest alarming!
The gas parts proven within the table above indicate the quantity of heat which shall be generated by burning 1kg of the common cable insulations tabled. Certainly this heat will speed up the burning of other adjacent supplies and should help spread the hearth in a constructing but importantly, in order to generate the warmth power, oxygen must be consumed. The higher the heat of combustion the extra oxygen is needed, so by selecting insulations with excessive gasoline components is including considerably to at least four of the first dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it is best to install polymeric cables inside steel conduits. This will definitely assist flame unfold and reduce smoke as a outcome of contained in the conduit oxygen is limited; nevertheless this is not an answer. As mentioned previously, many of the gasses from the decomposing polymeric insulations contained in the conduits are highly flammable and poisonous. These gases will migrate alongside the conduits to junction packing containers, switch 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, change or relay inflicting the hearth to unfold to another location.
Conclusion
The popularity of “Halogen Free” while ignoring the other toxic components of fire is a transparent admission we do not understand the subject properly nor can we simply define the dangers of mixed toxic elements or human physiological response to them. It is essential nonetheless, that we don’t proceed to design with only half an understanding of the issue. While no excellent resolution exists for natural primarily based cables, we can certainly decrease these critically necessary results of fireside risk:
One option possibly to choose cable insulations and jacket supplies that are halogen free and have a low fuel factor, then set up them in steel conduit or possibly the American approach is best: to use highly halogenated insulations in order that in case of fire any flame unfold is minimized.
For most power, management, communication and data circuits there is one complete resolution 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 provide a complete and complete reply to all the problems related to the fire security of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make positive the cable is effectively hearth proof. MICC cables don’t have any natural content so simply can not propagate flame or generate any smoke. The zero gas load ensures no warmth is added and no oxygen is consumed.
Being inorganic MICC cables can not generate any halogen or poisonous gasses at all together with CO.
Unfortunately many widespread cable fireplace check strategies used right now could inadvertently mislead folks into believing the polymeric flexible cable products they purchase and use will carry out as anticipated in all fireplace situations. As outlined in this paper, sadly this may not be right.
For extra data, go to www.temperature-house.com
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