Often the best flame retardant cables are halogenated as a end result of each the insulation and outer Jacket are flame retardant however when we want Halogen Free cables we discover it is often only the outer jacket which is flame retardant and the internal insulation isn’t.
This has significance because whereas cables with a flame retardant outer jacket will typically cross flame retardance exams with external flame, the same cables when subjected to excessive overload or extended brief circuits have proved in college tests to be extremely flammable and can even start a hearth. This impact is thought and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s maybe stunning that there aren’t any widespread test protocols for this seemingly widespread event and one cited by each authorities and media as cause of building fires.
Further, in Flame Retardant test methods similar to IEC60332 parts 1 & three which employ an exterior flame source, the cable samples aren’t pre-conditioned to regular working temperature but tested at room temperature. This oversight is essential particularly for energy circuits because the temperature index of the cable (the temperature at which the cable materials will self-support combustion in regular air) might be significantly affected by its beginning temperature i.e.: The hotter the cable is, the extra easily it’s going to propagate fire.
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 shoppers alike to supply a dependable indication of a cables capacity to retard the propagation of fire.
If we can’t trust the Standards what can we do?
In the USA many constructing requirements do not require halogen free cables. Certainly this is not because Americans are not properly knowledgeable of the dangers; rather the method taken is that: “It is better to have highly flame retardant cables which don’t propagate fire than minimally flame retardant cables which may spread a fire” – (a small hearth with some halogen could additionally be better than a large 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 lots of nations all over the world adopt a special mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is rather 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 tests for cables in USA resulting in the conclusion that common tests in UK and Europe might simply be exams the cables can pass somewhat than exams the cables ought to pass.
Conclusion
For most flexible polymeric cables the selection stays at present between high flame propagation efficiency with halogens or lowered flame propagation performance without halogens.
Enclosing cables in steel conduit will cut back propagation on the point of fireside but hydrocarbon based mostly combustion gasses from decomposing polymers are doubtless propagate through the conduits to switchboards, distribution boards and junction boxes in different parts of the building. Any spark such as the opening or closing of circuit breakers, or contactors is more probably to ignite the combustible gasses resulting in explosion and spreading the fire to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there’s typically no singe good answer for every installation so designers want to evaluate the required efficiency on a “project-by-project” foundation to determine which know-how is perfect.
The major significance of fireplace load
Inside all buildings and projects electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts operating. It powers computers, office gear and offers the connection for our phone and computers. Even our cell phones want to attach with wireless or GSM antennas that are connected to the telecom network by fiber optic or copper cables. Cables ensure our security by connecting
fireplace alarms, emergency voice communication, CCTV, smoke shutters, air pressurization followers, emergency lighting, fire sprinkler pumps, smoke and heat detectors, and so many other options of a modern Building Management System.
Where public safety is necessary we frequently request cables to have added security options similar to flame retardance to ensure the cables don’t simply unfold hearth, circuit integrity during fire in order that important fire-fighting and life safety equipment hold working. Sometimes we may acknowledge that the combustion of electrical cables produces smoke and this could be poisonous 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 buy and install might be safer
Because cables are put in by many various trades for various applications and are mostly hidden or embedded in our constructions, what is usually not realized is that the various miles of cables and tons of plastic polymers which make up the cables can characterize one of many largest hearth masses in the constructing. This point is definitely value pondering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are mostly primarily based on hydrocarbon polymers. These base materials aren’t usually flame retardant and naturally have a high fire load. Cable manufacturers make them flame retardant by adding compounds and chemicals. Certainly this improves the volatility of burning but the gasoline content of the base polymers remains.
Tables 1 and 2 above evaluate the hearth load in MJ/Kg for widespread cable insulating materials in opposition to some frequent fuels. The Heat Release Rate and volatility in air for these supplies will differ however the gas added to a fireplace per kilogram and the consequential volume of warmth generated and oxygen consumed is relative.
The volume in kilometers and tons of cables put in in our buildings and the related hearth load of the insulations is appreciable. This is particularly essential in projects with long egress times like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When contemplating hearth security we must first understand crucial factors. Fire consultants inform us most fireplace related deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma brought on by jumping in attempting to flee these effects.
Smoke
The first and most important aspect of smoke is how a lot smoke? Typically the bigger the hearth the more smoke is generated so anything we are ready to do to scale back the spread of fire may even correspondingly scale back the quantity of smoke.
Smoke will include particulates of carbon, ash and different solids, liquids and gasses, many are poisonous and combustible. 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 increased amounts of smoke and toxic byproducts together with CO and CO2. Presence of halogenated supplies will launch toxic Halides like Hydrogen Chloride together with many other poisonous and flammable gasses within the smoke.
For this purpose frequent smoke checks performed on cable insulation materials in massive three meter3 chambers with plenty of air can present misleading smoke figures as a end result of full burning will often release significantly much less smoke than partial incomplete burning which is likely in follow. Simply specifying IEC 61034 with a defined obscuration value then considering it will present a low smoke surroundings during fire could sadly be little of help for the individuals really involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and different nations undertake the idea of halogen free materials without correctly addressing the subject of toxicity. Halogens released during combustion are extremely poisonous however so too is carbon monoxide and this is not a halogen fuel. It is common to name for halogen free cables after which allow using Polyethylene as a result of it is halogen free. Burning Polyethylene (which can be seen from the desk above has the best MJ gas load per Kg of all insulations) will generate virtually 3 instances more heat than an equivalent PVC cable. This means is that burning polyethylene won’t solely generate almost 3 instances extra warmth but in addition devour virtually 3 occasions extra oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is answerable for most toxicity deaths in fires this situation is at finest alarming!
The fuel components proven in the table above point out the quantity of heat which will be generated by burning 1kg of the common cable insulations tabled. Certainly this warmth will accelerate the burning of different adjoining supplies and will help unfold the fire in a constructing but importantly, so as to generate the heat power, oxygen needs to be consumed. The greater the heat of combustion the more oxygen is needed, so by selecting insulations with high fuel components is adding considerably to no much less than 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 metallic conduits. This will certainly assist flame unfold and reduce smoke as a result of inside the conduit oxygen is restricted; nonetheless this isn’t a solution. As mentioned beforehand, เกจ์วัดแรงดันน้ำมันเครื่อง of the gasses from the decomposing polymeric insulations contained in the conduits are extremely flammable and poisonous. These gases will migrate along the conduits to junction boxes, change panels, distribution boards, motor control facilities, lamps, switches, and so forth. On entering the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, swap or relay causing the fireplace to unfold to another location.
Conclusion
The reputation of “Halogen Free” while ignoring the opposite poisonous parts of fire is a clear admission we don’t perceive the topic nicely nor can we easily outline the hazards of combined poisonous parts or human physiological response to them. It is important nevertheless, that we don’t continue to design with solely half an understanding of the issue. While no good solution exists for organic based mostly cables, we will certainly minimize these critically essential results of fireplace danger:
One option perhaps to choose cable insulations and jacket supplies that are halogen free and have a low gas element, then set up them in metal conduit or possibly the American method is healthier: to make use of highly halogenated insulations so that in case of fire any flame spread is minimized.
For most energy, management, communication and data circuits there could be one full solution out there 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 full answer to all the problems associated with the fireplace safety of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively fire proof. MICC cables don’t have any natural content so simply cannot propagate flame or generate any smoke. The zero gas load ensures no heat is added and no oxygen is consumed.
Being inorganic MICC cables can not generate any halogen or poisonous gasses in any respect together with CO.
Unfortunately many widespread cable fire test methods used today might inadvertently mislead folks into believing the polymeric flexible cable merchandise they purchase and use will carry out as anticipated in all hearth situations. As outlined in this paper, sadly this may not be right.
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