Often the most effective flame retardant cables are halogenated because each the insulation and outer Jacket are flame retardant however after we want Halogen Free cables we discover it is typically only the outer jacket which is flame retardant and the inside insulation is not.
This has significance as a result of whereas cables with a flame retardant outer jacket will typically pass flame retardance checks with exterior flame, the identical cables when subjected to excessive overload or extended quick circuits have proved in university checks to be highly flammable and may even begin a fire. This impact is understood and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is perhaps stunning that there aren’t any widespread take a look at protocols for this seemingly widespread event and one cited by each authorities and media as cause of constructing fires.
Further, in Flame Retardant take a look at methods corresponding to IEC60332 components 1 & three which employ an external flame source, the cable samples aren’t pre-conditioned to normal operating temperature however examined at room temperature. This oversight is essential especially for power circuits as a end result of the temperature index of the cable (the temperature at which the cable materials will self-support combustion in normal air) shall be significantly affected by its beginning temperature i.e.: The hotter the cable is, the more simply it’s going to propagate hearth.
It would appear that a need exists to re-evaluate current cable flame retardance test strategies as these are generally understood by consultants and consumers alike to offer a reliable 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 building standards do not require halogen free cables. Certainly this isn’t as a outcome of Americans aren’t wisely knowledgeable of the hazards; quite the strategy taken is that: “It is better to have extremely flame retardant cables which do not propagate fireplace than minimally flame retardant cables which may spread a fire” – (a small fire with some halogen could additionally be higher than a big fireplace with out halogens). One of the best methods to make a cable insulation and cable jacket extremely flame retardant is by using halogens.
Europe and a lot of nations around the globe undertake a special mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the fact is somewhat completely different: Flame propagation exams for cables as adopted in UK and Europe can arguably be mentioned to be less stringent than a variety of the flame propagation checks for cables in USA leading to the conclusion that widespread exams in UK and Europe could simply be checks the cables can pass quite than checks the cables ought to pass.
Conclusion
For most versatile polymeric cables the choice stays at present between high flame propagation efficiency with halogens or decreased flame propagation performance with out halogens.
Enclosing cables in metal conduit will scale back propagation at the point of fireplace but hydrocarbon based mostly combustion gasses from decomposing polymers are probably propagate through the conduits to switchboards, distribution boards and junction packing containers in other components of the building. Any spark such because the opening or closing of circuit breakers, or contactors is more doubtless to ignite the combustible gasses resulting in explosion and spreading the hearth to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide an answer, there is typically no singe good answer for each set up so designers need to judge the required performance on a “project-by-project” basis to resolve which technology is perfect.
The major significance of fireplace load
Inside all buildings and tasks electric cables present the connectivity which retains lights on, air-conditioning working and the lifts working. It powers computers, office gear and offers the connection for our telephone and computers. Even our mobile phones need to connect with wireless or GSM antennas that are linked to the telecom network by fiber optic or copper cables. Cables ensure our security 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 important we regularly request cables to have added security features such as flame retardance to make sure the cables do not easily spread hearth, circuit integrity throughout hearth so that important fire-fighting and life safety equipment hold working. Sometimes we could acknowledge that the combustion of electrical cables produces smoke and this can be toxic so we name for cables to be Low Smoke and Halogen Free. Logically and intuitively we expect that by requesting these particular properties the cables we purchase and set up shall be safer
Because cables are put in by many different trades for different applications 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 symbolize one of the greatest fire loads within the building. This level is definitely worth pondering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are largely based 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 including compounds and chemical compounds. Certainly this improves the volatility of burning however the fuel content material of the bottom polymers stays.
Tables 1 and a couple of above compare the hearth load in MJ/Kg for widespread cable insulating supplies towards some frequent fuels. The Heat Release Rate and volatility in air for these materials will differ but the gasoline added to a hearth per kilogram and the consequential volume of heat 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 especially essential in projects with long egress times like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When contemplating fire security we should first perceive an important components. Fire consultants tell us most fire associated deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma caused by leaping in making an attempt to flee these effects.
Smoke
The first and most important aspect of smoke is how much smoke? Typically the bigger the fire the more smoke is generated so anything we will do to minimize back the spread of fireside will also correspondingly cut back the quantity of smoke.
Smoke will comprise particulates of carbon, ash and other solids, liquids and gasses, many are toxic and flamable. In specific, fires in confined areas like buildings, tunnels and underground environments cause oxygen ranges to drop, this contributes to incomplete burning and smoldering which produces increased quantities of smoke and toxic byproducts together with CO and CO2. Presence of halogenated supplies will launch toxic Halides like Hydrogen Chloride together with many different toxic and flammable gasses within the smoke.
For this cause widespread smoke exams conducted on cable insulation supplies in giant three meter3 chambers with plenty of air can provide misleading smoke figures as a outcome of full burning will typically release significantly much less smoke than partial incomplete burning which is most likely going in follow. Simply specifying IEC 61034 with a defined obscuration worth then pondering it will present a low smoke setting throughout fireplace may sadly be little of assist for the individuals truly involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other international locations adopt the idea of halogen free supplies without correctly addressing the subject of toxicity. Halogens released throughout combustion are extremely poisonous but so too is carbon monoxide and this isn’t a halogen fuel. It is frequent to name for halogen free cables after which permit the utilization of Polyethylene because it’s halogen free. Burning Polyethylene (which could be seen from the desk above has the highest MJ gasoline load per Kg of all insulations) will generate nearly 3 times more heat than an equal PVC cable. This means is that burning polyethylene is not going to solely generate nearly 3 instances more heat but also devour nearly three occasions more oxygen and produce significantly more carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this case is at greatest alarming!
The gas elements shown within the table above point out the amount of heat which might be generated by burning 1kg of the widespread cable insulations tabled. Certainly this heat will accelerate the burning of different adjoining supplies and will assist spread the fire in a constructing but importantly, so as to generate the heat vitality, oxygen must be consumed. The larger the warmth of combustion the more oxygen is needed, so by choosing insulations with high gasoline components is including significantly to a minimal of four of the primary dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it is best to install polymeric cables inside metallic conduits. This will certainly assist flame spread and minimize smoke because contained in the conduit oxygen is proscribed; nonetheless this isn’t an answer. As stated beforehand, most 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, swap panels, distribution boards, motor control centers, lamps, switches, and so forth. On coming into the gases can ignite or explode with any arcing such because the make/break of a circuit breaker, contactor, swap or relay causing the hearth to spread to another location.
Conclusion
The popularity of “Halogen Free” while ignoring the other toxic components of fireplace is a clear admission we don’t understand the subject properly nor can we easily outline the risks of combined poisonous components or human physiological response to them. It is essential nevertheless, that we don’t proceed to design with only half an understanding of the problem. While no excellent solution exists for natural primarily based cables, we will definitely reduce these critically important effects of fireside risk:
One option possibly to choose cable insulations and jacket supplies which are halogen free and have a low gas factor, then set up them in steel conduit or maybe the American method is healthier: to use highly halogenated insulations so that in case of fire any flame spread is minimized.
For most energy, control, communication and information circuits there may be one complete answer available 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 complete and full reply to all the issues related to the hearth security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make sure the cable is successfully hearth proof. ตัววัดแรงดัน have no organic content material so simply can not propagate flame or generate any smoke. The zero gasoline load ensures no heat 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 frequent cable fireplace test methods used right now could inadvertently mislead folks into believing the polymeric flexible cable merchandise they buy and use will carry out as anticipated in all hearth conditions. As outlined on this paper, sadly this is probably not right.
For more information, go to www.temperature-house.com
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