Often 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 discover it is usually solely the outer jacket which is flame retardant and the internal insulation isn’t.
This has significance because while cables with a flame retardant outer jacket will typically move flame retardance exams with exterior flame, the identical cables when subjected to high overload or extended brief circuits have proved in university exams to be extremely flammable and may even begin a fireplace. This effect is known and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is perhaps shocking that there aren’t any widespread check protocols for this seemingly widespread occasion and one cited by both authorities and media as reason for building fires.
Further, in Flame Retardant test methods corresponding to IEC60332 parts 1 & three which make use of an external flame supply, the cable samples aren’t pre-conditioned to regular operating temperature but tested at room temperature. This oversight is essential especially 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 normal air) will be considerably affected by its starting temperature i.e.: The hotter the cable is, the more simply it will propagate fireplace.
It would seem that a want exists to re-evaluate current cable flame retardance take a look at methods as these are generally understood by consultants and customers alike to provide a reliable indication of a cables capability to retard the propagation of fireside.
If we can’t trust the Standards what do we do?
In the USA many building standards do not require halogen free cables. Certainly this isn’t as a end result of Americans aren’t correctly informed of the risks; quite the method taken is that: “It is best to have extremely flame retardant cables which don’t propagate fire than minimally flame retardant cables which can unfold a fire” – (a small fireplace with some halogen may be better than a big fire with out halogens). pressure gauge of one of the best methods to make a cable insulation and cable jacket extremely flame retardant is by using halogens.
Europe and plenty of nations around the world adopt a different mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the fact is quite different: Flame propagation tests for cables as adopted in UK and Europe can arguably be mentioned to be much less stringent than a variety of the flame propagation checks for cables in USA leading to the conclusion that common checks in UK and Europe may simply be tests the cables can pass rather than tests the cables ought to cross.
Conclusion
For most versatile polymeric cables the choice stays right now between high flame propagation performance with halogens or lowered flame propagation efficiency without halogens.
Enclosing cables in steel conduit will scale back propagation on the point of fireside but hydrocarbon based mostly combustion gasses from decomposing polymers are doubtless propagate by way of the conduits to switchboards, distribution boards and junction boxes in other parts of the building. Any spark such as the opening or closing of circuit breakers, or contactors is more likely to ignite the flamable gasses resulting in explosion and spreading the fireplace to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there may be often no singe good reply for every installation so designers need to evaluate the required efficiency on a “project-by-project” basis to resolve which know-how is perfect.
The major significance of fireplace load
Inside all buildings and initiatives electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts working. It powers computers, office gear and provides the connection for our phone and computer systems. Even our cellphones need to attach with wireless or GSM antennas which are linked to the telecom network by fiber optic or copper cables. Cables ensure our safety by connecting
hearth alarms, emergency voice communication, CCTV, smoke shutters, air pressurization followers, emergency lighting, hearth sprinkler pumps, smoke and warmth detectors, and so many different features of a contemporary Building Management System.
Where public security is necessary we often request cables to have added security features such as flame retardance to make sure the cables don’t simply spread fire, circuit integrity during fireplace in order that essential fire-fighting and life safety gear hold working. Sometimes we might acknowledge that the combustion of electric cables produces smoke and this can be toxic so we call for cables to be Low Smoke and Halogen Free. Logically and intuitively we think that by requesting these special properties the cables we buy and install will be safer
Because cables are put in by many alternative trades for different functions and are mostly 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 symbolize one of the biggest fireplace loads within the building. This point is actually worth pondering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are largely primarily based on hydrocarbon polymers. These base supplies are not typically flame retardant and naturally have a excessive hearth load. Cable producers make them flame retardant by including compounds and chemicals. Certainly this improves the volatility of burning however the gasoline content of the base polymers stays.
Tables 1 and 2 above evaluate the fire 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 fuel added to a hearth per kilogram and the consequential quantity of heat 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 considerable. This is particularly essential in tasks with long egress times like high rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When considering fireplace safety we must first understand an important components. Fire consultants tell us most fireplace related deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma brought on by leaping in making an attempt to flee these results.
Smoke
The first and most necessary side of smoke is how a lot smoke? Typically the bigger the fireplace the more smoke is generated so anything we will do to scale back the unfold of fire will also correspondingly reduce the amount of smoke.
Smoke will contain particulates of carbon, ash and other solids, liquids and gasses, many are poisonous and flamable. In diaphragm seal , fires in confined areas like buildings, tunnels and underground environments trigger oxygen levels to drop, this contributes to incomplete burning and smoldering which produces increased amounts of smoke and toxic byproducts together with CO and CO2. เพรสเชอร์เกจ of halogenated supplies will launch poisonous Halides like Hydrogen Chloride along with many different toxic and flammable gasses in the smoke.
For this purpose widespread smoke tests carried out on cable insulation materials in large 3 meter3 chambers with plenty of air can present misleading smoke figures because complete burning will typically release significantly less smoke than partial incomplete burning which is probably going in apply. Simply specifying IEC 61034 with an outlined obscuration value then pondering this can provide a low smoke surroundings throughout fireplace may sadly be little of help for the individuals actually concerned.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and different international locations undertake the idea of halogen free supplies with out properly addressing the topic of toxicity. Halogens launched throughout combustion are extraordinarily poisonous however so too is carbon monoxide and this isn’t a halogen gasoline. It is widespread to name for halogen free cables after which permit the use of Polyethylene as a outcome of it’s halogen free. Burning Polyethylene (which could be seen from the table above has the highest MJ gas load per Kg of all insulations) will generate nearly three instances extra heat than an equivalent PVC cable. This means is that burning polyethylene won’t only generate nearly three times more heat but also devour virtually three occasions more oxygen and produce significantly more carbon monoxide. Given carbon monoxide is answerable for most toxicity deaths in fires this example is at finest alarming!
The fuel parts shown within the table above point out the quantity of warmth which will be generated by burning 1kg of the frequent cable insulations tabled. Certainly this warmth will speed up the burning of other adjoining materials and should help unfold the hearth in a building however importantly, to be able to generate the warmth power, oxygen must be consumed. The greater the warmth of combustion the more oxygen is required, so by choosing insulations with excessive gasoline components is including significantly to no less than 4 of the first dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to put in polymeric cables inside metal conduits. This will certainly help flame unfold and minimize smoke as a result of inside the conduit oxygen is proscribed; nonetheless this is not a solution. As stated previously, most of the gasses from the decomposing polymeric insulations inside the conduits are highly flammable and toxic. These gases will migrate along the conduits to junction bins, change panels, distribution boards, motor management centers, lamps, switches, and so on. 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 causing the hearth to spread to a different location.
Conclusion
The reputation of “Halogen Free” while ignoring the other poisonous elements of fireside is a clear admission we do not perceive the subject nicely nor can we easily outline the hazards of mixed toxic parts or human physiological response to them. It is essential nonetheless, that we don’t continue to design with only half an understanding of the issue. While no good answer exists for natural based cables, we are able to definitely reduce these critically essential effects of fireplace risk:
One choice maybe to decide on cable insulations and jacket supplies which are halogen free and have a low fuel factor, then set up them in steel conduit or maybe the American method is best: to use extremely halogenated insulations in order that in case of fireplace any flame spread is minimized.
For most energy, control, communication and knowledge circuits there is one full resolution out there for all the problems raised on this paper. It is an answer which has been used reliably for over eighty years. MICC cables can provide a complete and full answer to all the problems associated with the fireplace security of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively fire proof. MICC cables haven’t any natural content material so simply 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 can’t generate any halogen or poisonous gasses in any respect together with CO.
Unfortunately many frequent cable fire take a look at methods used right now might inadvertently mislead folks into believing the polymeric versatile cable merchandise they purchase and use will perform as expected in all hearth conditions. As outlined in this paper, sadly this may not be right.
For more data, go to www.temperature-house.com
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