Often the most effective flame retardant cables are halogenated as a end result of each the insulation and outer Jacket are flame retardant but when we want Halogen Free cables we discover it’s usually only the outer jacket which is flame retardant and the inner insulation is not.
This has significance because while cables with a flame retardant outer jacket will often cross flame retardance exams with external flame, the identical cables when subjected to excessive overload or prolonged short circuits have proved in university checks to be highly flammable and can even start a fireplace. This effect is thought and printed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is maybe surprising that there aren’t any widespread take a look at protocols for this seemingly frequent event and one cited by both authorities and media as reason for constructing fires.
Further, in Flame Retardant check strategies corresponding to IEC60332 parts 1 & 3 which employ an external flame source, the cable samples usually are not pre-conditioned to regular working temperature but tested at room temperature. This oversight is important particularly 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) might be significantly affected by its beginning temperature i.e.: The hotter the cable is, the extra easily it’s going to propagate hearth.
It would seem that a need exists to re-evaluate present cable flame retardance test methods as these are commonly understood by consultants and shoppers alike to offer 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 constructing requirements do not require halogen free cables. Certainly this isn’t as a end result of Americans usually are not properly knowledgeable of the hazards; quite the method taken is that: “It is better to have extremely flame retardant cables which do not propagate fire than minimally flame retardant cables which can spread a fire” – (a small fire with some halogen may be higher than a large fire with out halogens). One of the most effective ways to make a cable insulation and cable jacket extremely flame retardant is through the use of halogens.
Europe and many nations all over the world adopt a unique mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is rather different: Flame propagation tests for cables as adopted in UK and Europe can arguably be said to be less stringent than a variety of the flame propagation exams for cables in USA resulting in the conclusion that frequent checks in UK and Europe may simply be checks the cables can cross quite than checks the cables should move.
For most versatile polymeric cables the choice remains right now between excessive flame propagation performance with halogens or lowered flame propagation efficiency without halogens.
Enclosing cables in metal conduit will cut back propagation on the level of fireside however hydrocarbon based mostly combustion gasses from decomposing polymers are doubtless propagate by way of the conduits to switchboards, distribution boards and junction bins in different elements of the constructing. Any spark such because the opening or closing of circuit breakers, or contactors is likely to ignite the combustible gasses resulting in explosion and spreading the hearth to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would offer a solution, there is typically no singe good reply for each installation so designers want to evaluate the required performance on a “project-by-project” basis to decide which technology is perfect.
The major significance of fire load
Inside all buildings and tasks electric cables provide the connectivity which keeps lights on, air-conditioning working and the lifts working. It powers computer systems, workplace gear and provides the connection for our phone and computer systems. Even our cellphones need to attach with wi-fi or GSM antennas which are linked to the telecom community by fiber optic or copper cables. Cables guarantee our safety by connecting
fireplace alarms, emergency voice communication, CCTV, smoke shutters, air pressurization fans, emergency lighting, fireplace sprinkler pumps, smoke and warmth detectors, and so many different options of a contemporary Building Management System.
Where public security is important we often request cables to have added safety features corresponding to flame retardance to ensure the cables do not easily spread hearth, circuit integrity throughout hearth in order that important fire-fighting and life safety gear hold working. Sometimes we might recognize that the combustion of electrical cables produces smoke and this could 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 buy and install might be safer
Because cables are installed by many alternative trades for different purposes and are largely hidden or embedded in our constructions, what is commonly 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 loads in the building. This level is actually worth pondering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are principally 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 chemical substances. Certainly this improves the volatility of burning but the gasoline content material of the bottom polymers remains.
Tables 1 and a pair of above examine the fire load in MJ/Kg for common cable insulating materials in opposition to some widespread fuels. The Heat Release Rate and volatility in air for these materials will differ however the gasoline added to a fire per kilogram and the consequential quantity of heat generated and oxygen consumed is relative.
The volume in kilometers and tons of cables put in in our buildings and the associated hearth load of the insulations is considerable. This is especially necessary in initiatives with long egress times like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so on.
When contemplating fire safety we should first understand an important components. Fire experts tell us most hearth related deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma caused by jumping in attempting to escape these results.
The first and most essential facet of smoke is how much smoke? Typically the larger the hearth the more smoke is generated so anything we are ready to do to reduce back the unfold of fireplace will also correspondingly cut back the amount of smoke.
Smoke will contain particulates of carbon, ash and other solids, liquids and gasses, many are poisonous and combustible. In specific, 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 quantities of smoke and toxic byproducts together with CO and CO2. Presence of halogenated materials will release poisonous Halides like Hydrogen Chloride along with many different poisonous and flammable gasses within the smoke.
For this cause widespread smoke checks performed on cable insulation materials in massive 3 meter3 chambers with loads of air can present misleading smoke figures as a outcome of complete burning will typically launch significantly less smoke than partial incomplete burning which is most likely going in practice. Simply specifying IEC 61034 with an outlined obscuration worth then thinking it will provide a low smoke environment during fire might unfortunately be little of help for the people 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 materials with out properly addressing the topic of toxicity. Halogens launched during combustion are extraordinarily toxic however so too is carbon monoxide and this isn’t a halogen gas. It is widespread to name for halogen free cables and then allow using Polyethylene as a outcome 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 nearly three times more heat than an equal PVC cable. This means is that burning polyethylene won’t only generate almost 3 occasions more warmth but also devour nearly three occasions more oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is responsible for most toxicity deaths in fires this case is at greatest alarming!
The gasoline components shown within the table above indicate the amount of heat which shall be generated by burning 1kg of the common cable insulations tabled. Certainly this warmth will speed up the burning of other adjacent materials and may help unfold the fireplace in a constructing however importantly, so as to generate the warmth energy, oxygen needs to be consumed. เกจวัดแรงดัน of combustion the more oxygen is required, so by choosing insulations with high gasoline elements is adding considerably to at least 4 of the primary dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to put in polymeric cables inside steel conduits. This will certainly assist flame spread and decrease smoke as a end result of contained in the conduit oxygen is proscribed; nonetheless this isn’t an answer. As said previously, most of the gasses from the decomposing polymeric insulations contained in the conduits are extremely flammable and toxic. These gases will migrate along the conduits to junction packing containers, switch panels, distribution boards, motor control centers, lamps, switches, and so on. On getting into the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, change or relay inflicting the hearth to unfold to a different location.
The recognition of “Halogen Free” while ignoring the opposite poisonous parts of fire is a transparent admission we do not perceive the subject well nor can we easily outline the risks of mixed toxic parts or human physiological response to them. It is essential however, that we don’t continue to design with only half an understanding of the issue. While no good solution exists for organic primarily based cables, we will actually decrease these critically essential results of fire danger:
One option maybe to choose on cable insulations and jacket supplies which are halogen free and have a low fuel component, then set up them in metal conduit or perhaps the American method is healthier: to use extremely halogenated insulations so that in case of fire any flame spread is minimized.
For most power, management, communication and knowledge circuits there could be one complete answer available for all the issues 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 answer to all the issues related to the hearth security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC ensure the cable is effectively hearth proof. MICC cables have no natural content material so merely cannot propagate flame or generate any smoke. The zero fuel load ensures no warmth is added and no oxygen is consumed.
Being inorganic MICC cables cannot generate any halogen or poisonous gasses in any respect including CO.
Unfortunately many common cable hearth check strategies 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 situations. As outlined on this paper, sadly this will not be right.
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