Often the most effective flame retardant cables are halogenated as a result of both the insulation and outer Jacket are flame retardant however once we want Halogen Free cables we discover it’s often solely the outer jacket which is flame retardant and the internal insulation just isn’t.
This has significance as a result of whereas cables with a flame retardant outer jacket will typically move flame retardance tests with external flame, the identical cables when subjected to excessive overload or prolonged brief circuits have proved in university tests to be extremely flammable and might even begin a hearth. This impact is known and revealed (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is maybe shocking that there aren’t any common test protocols for this seemingly frequent occasion and one cited by each authorities and media as explanation for building fires.
Further, in Flame Retardant check methods similar to IEC60332 elements 1 & three which make use of an external flame source, the cable samples are not pre-conditioned to normal operating temperature but examined at room temperature. This oversight is important particularly 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) might be considerably affected by its starting 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 present cable flame retardance test strategies as these are commonly understood by consultants and customers alike to supply a reliable indication of a cables capability to retard the propagation of fireside.
If we can’t trust the Standards what will we do?
In the USA many building standards don’t require halogen free cables. Certainly this is not as a result of Americans are not correctly knowledgeable of the hazards; somewhat the approach taken is that: “It is better to have highly flame retardant cables which don’t propagate fireplace than minimally flame retardant cables which can unfold a fire” – (a small fire with some halogen may be higher than a big fire with out halogens). One of the most effective ways to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and lots of countries all over the world undertake a unique mentality: Halogen Free and Flame Retardant. Whilst that is an admirable mandate the truth is somewhat totally different: Flame propagation checks for cables as adopted in UK and Europe can arguably be stated to be less stringent than a few of the flame propagation checks for cables in USA resulting in the conclusion that frequent tests in UK and Europe could merely be exams the cables can move rather than checks the cables should move.
Conclusion
For most flexible polymeric cables the choice remains at present between high flame propagation efficiency with halogens or lowered flame propagation efficiency with out halogens.
Enclosing cables in steel conduit will reduce propagation at the point of fireplace but hydrocarbon primarily based combustion gasses from decomposing polymers are likely propagate by way of the conduits to switchboards, distribution boards and junction packing containers in different components of the building. ร้านซ่อมเครื่องวัดความดัน because the opening or closing of circuit breakers, or contactors is prone to ignite the combustible gasses resulting in explosion and spreading the fireplace to a different location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there’s often no singe good answer for each set up so designers want to gauge the required performance on a “project-by-project” foundation to decide which expertise is perfect.
The main importance of fireplace load
Inside all buildings and tasks electrical cables provide the connectivity which retains lights on, air-conditioning working and the lifts operating. It powers computer systems, workplace equipment and provides the connection for our phone and computer systems. Even our cellphones want to connect with wi-fi or GSM antennas that are linked to the telecom community by fiber optic or copper cables. Cables guarantee our safety by connecting
hearth alarms, emergency voice communication, CCTV, smoke shutters, air pressurization followers, emergency lighting, fire sprinkler pumps, smoke and heat 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 options such as flame retardance to ensure the cables don’t easily unfold fireplace, circuit integrity during hearth so that important fire-fighting and life security tools hold working. Sometimes we may recognize that the combustion of electrical cables produces smoke and this may 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 set up will be safer
Because cables are installed by many alternative trades for different functions and are principally hidden or embedded in our constructions, what is often not realized is that the various miles of cables and tons of plastic polymers which make up the cables can represent one of the biggest hearth loads within the constructing. This level is definitely worth thinking 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 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 fuel content material of the base polymers stays.
Tables 1 and 2 above evaluate the fire load in MJ/Kg for frequent cable insulating materials towards some common fuels. The Heat Release Rate and volatility in air for these materials will differ however the gas added to a hearth per kilogram and the consequential volume of warmth generated and oxygen consumed is relative.
The quantity in kilometers and tons of cables put in in our buildings and the associated fireplace load of the insulations is considerable. This is especially important in projects with lengthy egress times like high rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When contemplating hearth security we should first understand crucial elements. Fire consultants tell us most fire associated deaths in buildings are caused by smoke inhalation, temperature rise and oxygen depletion or by trauma brought on by leaping in trying to flee these results.
Smoke
The first and most essential facet of smoke is how a lot smoke? Typically the bigger the hearth the more smoke is generated so something we can do to cut back the spread of fire may also correspondingly cut back the amount of smoke.
Smoke will include 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 amounts of smoke and toxic byproducts together with CO and CO2. Presence of halogenated materials will release toxic Halides like Hydrogen Chloride along with many other toxic and flammable gasses in the smoke.
For this reason common smoke checks conducted on cable insulation supplies in large three meter3 chambers with loads of air can provide deceptive smoke figures because complete burning will typically release significantly 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 provide a low smoke setting during fireplace could unfortunately be little of assist for the folks actually involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and different countries undertake the concept of halogen free materials without properly addressing the subject of toxicity. Halogens released throughout combustion are extraordinarily poisonous however so too is carbon monoxide and this is not a halogen gas. It is widespread to call for halogen free cables after which allow the use of Polyethylene because it is halogen free. Burning Polyethylene (which may be seen from the desk above has the very best MJ fuel load per Kg of all insulations) will generate nearly 3 occasions more heat than an equivalent PVC cable. This means is that burning polyethylene is not going to solely generate virtually 3 occasions extra heat but in addition eat virtually three occasions extra oxygen and produce significantly more carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this situation is at greatest alarming!
The gasoline parts proven within the desk above point out the quantity of warmth which might be generated by burning 1kg of the common cable insulations tabled. Certainly this heat will accelerate the burning of other adjoining materials and will help unfold the hearth in a constructing however importantly, to have the ability to generate the heat vitality, oxygen must be consumed. The larger the warmth of combustion the more oxygen is required, so by choosing insulations with high gasoline parts is including considerably to at least 4 of the primary dangers of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it is best to put in polymeric cables inside metallic conduits. This will certainly help flame unfold and decrease smoke as a result of inside the conduit oxygen is restricted; nonetheless this isn’t an answer. As said previously, many of the gasses from the decomposing polymeric insulations inside the conduits are extremely flammable and toxic. These gases will migrate alongside the conduits to junction packing containers, change panels, distribution boards, motor management centers, lamps, switches, and so on. On getting into the gases can ignite or explode with any arcing such because the make/break of a circuit breaker, contactor, switch or relay inflicting the fire to spread to a different location.
Conclusion
The reputation of “Halogen Free” whereas ignoring the opposite poisonous parts of fire is a transparent admission we don’t perceive the topic nicely nor can we simply outline the risks of mixed toxic components or human physiological response to them. It is important nonetheless, that we do not continue to design with only half an understanding of the problem. While no perfect resolution exists for organic based mostly cables, we are in a position to definitely decrease these critically important effects of fireside threat:
One possibility possibly to determine on cable insulations and jacket materials that are halogen free and have a low gasoline factor, then set up them in metal conduit or possibly the American approach is best: to use extremely halogenated insulations so that in case of fireside any flame unfold is minimized.
For most energy, control, communication and information circuits there may be one full solution available for all the problems raised in this paper. It is an answer which has been used reliably for over eighty years. MICC cables can provide a total and full reply to all the problems associated with the fireplace safety of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make sure the cable is successfully fireplace proof. MICC cables have no organic content so simply can’t propagate flame or generate any smoke. The zero gas 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 fire test methods used right now might inadvertently mislead people into believing the polymeric versatile cable products they buy and use will perform as anticipated in all hearth conditions. As outlined on this paper, sadly this will not be appropriate.
For more info, go to www.temperature-house.com
Share