Often one of the best flame retardant cables are halogenated because both the insulation and outer Jacket are flame retardant but after we want Halogen Free cables we discover it is often only the outer jacket which is flame retardant and the internal insulation just isn’t.
This has significance because whereas cables with a flame retardant outer jacket will typically pass flame retardance tests with external flame, the same cables when subjected to high overload or prolonged quick circuits have proved in college tests to be extremely flammable and can even begin a fire. This impact is thought and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is maybe surprising that there are no widespread take a look at protocols for this seemingly common event and one cited by both authorities and media as explanation for constructing fires.
Further, in Flame Retardant take a look at strategies corresponding to IEC60332 components 1 & three which employ an external flame supply, the cable samples aren’t pre-conditioned to normal working temperature but examined at room temperature. This oversight is necessary 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 regular air) will be significantly affected by its starting temperature i.e.: The hotter the cable is, the more easily it will propagate fireplace.
It would appear that a need exists to re-evaluate current cable flame retardance check methods as these are commonly understood by consultants and customers alike to provide a dependable indication of a cables capacity to retard the propagation of fireside.
If we can’t belief the Standards what can we do?
In the USA many constructing requirements do not require halogen free cables. Certainly this is not as a outcome of Americans aren’t wisely informed of the risks; rather the method taken is that: “It is better to have highly flame retardant cables which do not propagate hearth than minimally flame retardant cables which can unfold a fire” – (a small hearth with some halogen could additionally be better than a large fire 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 tons of countries all over the world adopt a different mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the reality is quite completely different: Flame propagation tests for cables as adopted in UK and Europe can arguably be said to be less stringent than some of the flame propagation tests for cables in USA leading to the conclusion that common checks in UK and Europe could merely be checks the cables can pass quite than tests the cables ought to pass.
Conclusion
For most flexible polymeric cables the choice stays at present between excessive flame propagation performance with halogens or decreased flame propagation efficiency without halogens.
Enclosing cables in steel conduit will scale back propagation on the level of fireside but hydrocarbon based combustion gasses from decomposing polymers are probably propagate through the conduits to switchboards, distribution boards and junction bins in other parts of the constructing. Any spark such as the opening or closing of circuit breakers, or contactors is likely to ignite the flamable gasses leading to explosion and spreading the fire to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there is often no singe good reply for each installation so designers need to gauge the required efficiency on a “project-by-project” basis to decide which technology is perfect.
The primary importance of fire load
Inside all buildings and initiatives electrical cables present the connectivity which keeps lights on, air-conditioning working and the lifts running. It powers computer systems, office tools and provides the connection for our phone and computers. Even our cellphones need to connect 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 followers, emergency lighting, hearth sprinkler pumps, smoke and warmth detectors, and so many other features of a modern Building Management System.
Where public safety is important we frequently request cables to have added security features corresponding to flame retardance to make sure the cables don’t easily unfold fire, circuit integrity during fire so that essential fire-fighting and life security tools maintain working. Sometimes we may recognize 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 special properties the cables we buy and install might be safer
Because cables are put in by many various trades for various functions and are principally 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 represent one of many biggest fireplace hundreds in the building. This point is definitely value considering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable materials are principally based on hydrocarbon polymers. These base supplies aren’t usually flame retardant and naturally have a high hearth load. Cable producers make them flame retardant by adding compounds and chemical compounds. Certainly this improves the volatility of burning however the fuel content material of the base polymers remains.
Tables 1 and 2 above evaluate the hearth load in MJ/Kg for common cable insulating supplies in opposition to some frequent fuels. เพรสเชอร์เกจดิจิตอล and volatility in air for these supplies will differ however the fuel added to a fire per kilogram and the consequential volume of warmth generated and oxygen consumed is relative.
The quantity in kilometers and tons of cables installed in our buildings and the related fireplace load of the insulations is appreciable. This is especially necessary in tasks with lengthy egress occasions like high rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When considering hearth safety we must first understand crucial components. Fire experts tell us most hearth associated deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma attributable to leaping in making an attempt to escape these effects.
Smoke
The first and most essential facet of smoke is how a lot smoke? Typically the larger the fireplace the extra smoke is generated so something we will do to reduce the unfold of fireplace may also correspondingly cut back the quantity of smoke.
Smoke will comprise 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 cause oxygen levels to drop, this contributes to incomplete burning and smoldering which produces increased quantities of smoke and poisonous byproducts together with CO and CO2. Presence of halogenated materials will release poisonous Halides like Hydrogen Chloride together with many different poisonous and flammable gasses within the smoke.
For this reason frequent smoke tests carried out on cable insulation materials in massive three meter3 chambers with loads of air can present misleading smoke figures because full burning will often release significantly much less smoke than partial incomplete burning which is likely in follow. Simply specifying IEC 61034 with an outlined obscuration worth then considering this will present a low smoke surroundings throughout fire may sadly be little of help for the people truly concerned.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other international locations undertake the idea of halogen free supplies without properly addressing the topic of toxicity. Halogens launched during combustion are extremely poisonous however so too is carbon monoxide and this isn’t a halogen gasoline. It is frequent to call for halogen free cables and then permit the use of Polyethylene because it’s halogen free. Burning Polyethylene (which could be seen from the desk above has the very best MJ fuel load per Kg of all insulations) will generate almost three instances extra warmth than an equal PVC cable. This means is that burning polyethylene won’t only generate nearly 3 instances extra heat but in addition eat virtually three instances extra 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 elements proven within the desk above point out the amount of heat which will be generated by burning 1kg of the widespread cable insulations tabled. Certainly this heat will accelerate the burning of different adjacent supplies and will assist unfold the fireplace in a building however importantly, so as to generate the heat vitality, oxygen needs to be consumed. The higher the warmth of combustion the extra oxygen is needed, so by choosing insulations with excessive gasoline parts is including significantly to no much 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 metallic conduits. This will definitely assist flame unfold and minimize smoke because contained in the conduit oxygen is limited; however this isn’t an answer. As stated beforehand, most of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and toxic. These gases will migrate along the conduits to junction boxes, switch panels, distribution boards, motor management centers, lamps, switches, etc. On entering the gases can ignite or explode with any arcing such because the make/break of a circuit breaker, contactor, switch or relay causing the fire to unfold to a different location.
Conclusion
The recognition of “Halogen Free” whereas ignoring the opposite toxic components of fire is a clear admission we do not understand the subject nicely nor can we simply define the hazards of mixed poisonous elements or human physiological response to them. It is important however, that we do not proceed to design with only half an understanding of the issue. While no perfect answer exists for natural based cables, we can actually reduce these critically important results of fireplace danger:
One option maybe to choose on cable insulations and jacket materials which are halogen free and have a low gasoline component, then set up them in metal conduit or perhaps the American approach is healthier: to make use of highly halogenated insulations in order that in case of fireplace any flame unfold is minimized.
For most power, control, communication and knowledge circuits there could be one full resolution obtainable for all the issues raised in this paper. It is an answer which has been used reliably for over 80 years. MICC cables can present a complete and complete answer to all the problems related to the hearth security of organic polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is successfully fire proof. MICC cables have no organic content material so simply cannot 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 at all including CO.
Unfortunately many widespread cable fire take a look at methods used right now may inadvertently mislead individuals into believing the polymeric flexible cable merchandise they purchase and use will perform as anticipated in all hearth situations. As outlined on this paper, sadly this is in all probability not appropriate.
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