Often one of the best flame retardant cables are halogenated because both the insulation and outer Jacket are flame retardant however when we want Halogen Free cables we find it is often only the outer jacket which is flame retardant and the internal insulation isn’t.
This has significance as a result of while cables with a flame retardant outer jacket will often move flame retardance exams with exterior flame, the identical cables when subjected to excessive overload or prolonged short circuits have proved in college checks to be highly flammable and can even begin a fireplace. This effect is understood and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s maybe shocking that there are no frequent take a look at protocols for this seemingly widespread event and one cited by each authorities and media as reason for building fires.
Further, in Flame Retardant take a look at methods corresponding to IEC60332 parts 1 & 3 which make use of an exterior flame supply, the cable samples usually are not pre-conditioned to regular operating temperature but examined at room temperature. This oversight is necessary especially for energy circuits because the temperature index of the cable (the temperature at which the cable material will self-support combustion in normal air) shall be significantly affected by its starting temperature i.e.: The hotter the cable is, the extra easily it will propagate fire.
It would seem that a need exists to re-evaluate present cable flame retardance take a look at strategies as these are commonly understood by consultants and consumers alike to provide a reliable indication of a cables capability to retard the propagation of fireplace.
If we can’t trust the Standards what will we do?
In the USA many building requirements don’t require halogen free cables. Certainly this is not as a outcome of Americans are not correctly informed of the risks; quite the method 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 may be better than a large fire with out halogens). One of the best ways to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
compound gauge ราคา and many countries around the globe adopt a unique mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the truth is rather 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 checks for cables in USA leading to the conclusion that frequent exams in UK and Europe might merely be checks the cables can pass rather than tests the cables ought to move.
Conclusion
For most flexible polymeric cables the choice remains right now between high flame propagation efficiency with halogens or decreased flame propagation efficiency with out halogens.
Enclosing cables in steel conduit will reduce propagation on the level of fire however hydrocarbon based combustion gasses from decomposing polymers are probably propagate by way of the conduits to switchboards, distribution boards and junction packing containers in other parts of the building. Any spark such as the opening or closing of circuit breakers, or contactors is prone to ignite the combustible gasses leading to explosion and spreading the hearth to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there’s usually no singe excellent reply for each installation so designers need to judge the required efficiency on a “project-by-project” foundation to decide which expertise is optimal.
The major importance of fireplace load
Inside all buildings and tasks electric cables present the connectivity which retains lights on, air-conditioning working and the lifts running. It powers computers, office tools and provides the connection for our telephone and computer systems. Even our cellphones want 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
fire alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, hearth sprinkler pumps, smoke and warmth detectors, and so many other features of a modern Building Management System.
Where public security is important we regularly request cables to have added security options such as flame retardance to ensure the cables don’t easily unfold fireplace, circuit integrity during hearth in order that important fire-fighting and life safety gear maintain working. Sometimes we may recognize that the combustion of electric cables produces smoke and this might be toxic so we name for cables to be Low Smoke and Halogen Free. Logically and intuitively we think that by requesting these special properties the cables we purchase and install might be safer
Because cables are put in by many different trades for various applications and are principally hidden or embedded in our constructions, what is often not realized is that the many miles of cables and tons of plastic polymers which make up the cables can characterize one of many largest hearth masses in the building. This level is certainly worth considering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are mostly based on hydrocarbon polymers. These base supplies usually are not usually flame retardant and naturally have a excessive fire load. Cable producers make them flame retardant by adding compounds and chemical compounds. Certainly this improves the volatility of burning however the gasoline content of the bottom polymers stays.
Tables 1 and 2 above evaluate 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 fuel 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 associated fire load of the insulations is appreciable. This is particularly important in tasks with long egress instances like high rise, public buildings, tunnels and underground environments, airports, hospitals and so on.
When considering fire security we must first understand an important components. Fire specialists inform us most hearth associated deaths in buildings are caused by smoke inhalation, temperature rise and oxygen depletion or by trauma caused by leaping in trying to flee these effects.
Smoke
The first and most necessary aspect of smoke is how a lot smoke? Typically the bigger the fire the extra smoke is generated so anything we are ready to do to reduce back the spread of fireside may even correspondingly reduce the amount of smoke.
Smoke will contain particulates of carbon, ash and different solids, liquids and gasses, many are poisonous and combustible. In specific, 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 quantities of smoke and toxic byproducts including CO and CO2. Presence of halogenated supplies will release poisonous Halides like Hydrogen Chloride together with many different poisonous and flammable gasses in the smoke.
For this purpose widespread smoke tests conducted on cable insulation supplies in large three meter3 chambers with loads of air can provide deceptive smoke figures as a end result of full burning will usually release considerably much less smoke than partial incomplete burning which is likely in practice. Simply specifying IEC 61034 with an outlined obscuration worth then pondering it will present a low smoke surroundings during fire may sadly be little of assist for the individuals truly involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and different international locations adopt the idea of halogen free materials without properly addressing the topic of toxicity. Halogens released during combustion are extraordinarily toxic however so too is carbon monoxide and this isn’t a halogen gas. It is frequent to name for halogen free cables and then allow using Polyethylene as a result of it is halogen free. Burning Polyethylene (which may be seen from the desk above has the highest MJ fuel load per Kg of all insulations) will generate virtually three occasions more warmth than an equivalent PVC cable. This means is that burning polyethylene won’t only generate almost three instances extra heat but in addition devour almost 3 occasions extra oxygen and produce considerably more carbon monoxide. Given carbon monoxide is answerable for most toxicity deaths in fires this case is at finest alarming!
The gasoline components shown in the table above point out the quantity of warmth which shall be generated by burning 1kg of the frequent cable insulations tabled. Certainly this warmth will accelerate the burning of other adjacent materials and should assist spread the fire in a building but importantly, so as to generate the heat power, oxygen must be consumed. The higher the warmth of combustion the extra oxygen is needed, so by choosing insulations with excessive gas elements is adding significantly to no less than four of the first risks 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 decrease smoke as a outcome of inside the conduit oxygen is limited; however this isn’t an answer. As said beforehand, most of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and poisonous. These gases 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, switch or relay inflicting the hearth to spread to another location.
Conclusion
The popularity of “Halogen Free” whereas ignoring the opposite poisonous components of fire is a transparent admission we don’t perceive the topic well nor can we simply outline the risks of combined toxic parts or human physiological response to them. It is essential nonetheless, that we do not proceed to design with solely half an understanding of the issue. While no good resolution exists for natural based mostly cables, we can actually reduce these critically important results of fireside danger:
One possibility perhaps to determine on cable insulations and jacket supplies which are halogen free and have a low gas element, then set up them in steel conduit or perhaps the American method is better: to use highly halogenated insulations in order that in case of fireside any flame unfold is minimized.
For most energy, management, communication and information circuits there may be one full resolution obtainable for all the problems raised in this paper. It is a solution which has been used reliably for over eighty years. MICC cables can present a complete and complete reply to all the issues related to the fireplace security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make positive the cable is effectively hearth proof. MICC cables haven’t any organic content material so merely can’t 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 frequent cable hearth check methods used right now could inadvertently mislead people into believing the polymeric flexible cable merchandise they purchase and use will perform as anticipated in all hearth situations. As outlined in this paper, sadly this is most likely not appropriate.
For extra info, go to www.temperature-house.com
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