Often the best flame retardant cables are halogenated as a outcome of both the insulation and outer Jacket are flame retardant but once we want Halogen Free cables we discover it’s usually only the outer jacket which is flame retardant and the inside insulation just isn’t.
This has significance as a outcome of whereas cables with a flame retardant outer jacket will often move flame retardance checks with exterior flame, the same cables when subjected to high overload or prolonged short circuits have proved in college tests to be extremely flammable and can even start a fire. This impact is understood and published (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it’s perhaps shocking that there aren’t any frequent test protocols for this seemingly common event and one cited by each authorities and media as cause of constructing fires.
Further, in Flame Retardant check methods similar to IEC60332 components 1 & three which employ an exterior flame source, the cable samples are not pre-conditioned to normal working temperature however examined at room temperature. This oversight is necessary particularly for power circuits as a result of the temperature index of the cable (the temperature at which the cable material will self-support combustion in regular air) will be considerably affected by its beginning temperature i.e.: The hotter the cable is, the more easily it will propagate fireplace.
It would appear that a want exists to re-evaluate current cable flame retardance check methods as these are commonly understood by consultants and customers 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 isn’t as a end result of Americans are not wisely informed of the risks; somewhat the strategy taken is that: “It is best to have highly flame retardant cables which don’t propagate fireplace than minimally flame retardant cables which can spread a fire” – (a small fire with some halogen could also be better than a big fire with out halogens). One of the best ways to make a cable insulation and cable jacket extremely flame retardant is by utilizing halogens.
Europe and a lot of international locations around the globe adopt a unique mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the truth is rather different: Flame propagation checks for cables as adopted in UK and Europe can arguably be stated to be less stringent than some of the flame propagation checks for cables in USA leading to the conclusion that widespread checks in UK and Europe could merely be checks the cables can move quite than exams the cables ought to move.
Conclusion
For most flexible polymeric cables the selection remains at present between high flame propagation performance with halogens or reduced flame propagation efficiency with out halogens.
Enclosing cables in metal conduit will scale back propagation at the level of fireside however hydrocarbon based mostly combustion gasses from decomposing polymers are likely propagate through the conduits to switchboards, distribution boards and junction packing containers in other elements of the constructing. Any spark such as the opening or closing of circuit breakers, or contactors is more likely to ignite the flamable gasses leading to explosion and spreading the fireplace to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would provide a solution, there might be usually no singe perfect answer for each installation so designers want to evaluate the required performance on a “project-by-project” basis to resolve which expertise is optimal.
The main importance of fireplace load
Inside all buildings and projects electric cables provide the connectivity which keeps lights on, air-conditioning working and the lifts operating. It powers computer systems, workplace tools and provides the connection for our telephone and computer systems. Even our cellphones need to connect with wireless or GSM antennas that are related 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, fireplace sprinkler pumps, smoke and heat detectors, and so many different options of a contemporary Building Management System.
Where public security is important we frequently request cables to have added security features such as flame retardance to ensure the cables do not easily spread hearth, circuit integrity throughout fire so that essential fire-fighting and life security gear maintain working. Sometimes we might 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 think that by requesting these particular properties the cables we buy and install will be safer
Because cables are installed by many different trades for various functions and are principally hidden or embedded in our constructions, what is often not realized is that the numerous miles of cables and tons of plastic polymers which make up the cables can symbolize one of many greatest hearth masses within the constructing. This point is actually value considering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are principally based mostly on hydrocarbon polymers. These base materials are not usually flame retardant and naturally have a high fire load. Cable producers make them flame retardant by including compounds and chemical substances. Certainly this improves the volatility of burning however the gas content material of the bottom polymers stays.
Tables 1 and a pair of above examine the fireplace load in MJ/Kg for frequent cable insulating supplies in opposition to some common 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 quantity of heat generated and oxygen consumed is relative.
เกจ์ออกซิเจนsumo in kilometers and tons of cables installed in our buildings and the related hearth load of the insulations is considerable. This is particularly necessary in tasks with long egress occasions like excessive rise, public buildings, tunnels and underground environments, airports, hospitals and so forth.
When considering fireplace security we should first perceive crucial elements. Fire consultants inform us most fire related deaths in buildings are brought on by smoke inhalation, temperature rise and oxygen depletion or by trauma attributable to jumping in attempting to escape these results.
Smoke
The first and most essential side of smoke is how a lot smoke? Typically the larger the fire the more smoke is generated so something we are able to do to reduce back the unfold of fireplace will also correspondingly scale back the amount of smoke.
Smoke will include particulates of carbon, ash and different solids, liquids and gasses, many are poisonous and flamable. In specific, fires in confined areas like buildings, tunnels and underground environments trigger oxygen ranges 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 supplies will release poisonous Halides like Hydrogen Chloride together with many other poisonous and flammable gasses within the smoke.
For this cause widespread smoke checks performed on cable insulation supplies in massive three meter3 chambers with plenty of air can present deceptive smoke figures as a result of full burning will typically release significantly less smoke than partial incomplete burning which is likely in apply. Simply specifying IEC 61034 with a defined obscuration value then thinking this will present a low smoke environment throughout fire may sadly be little of help for the people actually concerned.
เกจวัดแรงดันน้ำ10บาร์ , Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is regarding that Europe and other international locations adopt the concept of halogen free supplies with out correctly addressing the subject of toxicity. Halogens released during combustion are extraordinarily poisonous however so too is carbon monoxide and this isn’t a halogen gas. It is frequent to call for halogen free cables after which permit the usage of Polyethylene as a end result of it’s halogen free. Burning Polyethylene (which may be seen from the table above has the best MJ fuel load per Kg of all insulations) will generate nearly 3 instances extra heat than an equal PVC cable. This means is that burning polyethylene is not going to solely generate almost 3 occasions more warmth but in addition eat almost three instances extra oxygen and produce significantly more carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this case is at finest alarming!
The gas elements shown in the desk above indicate the amount of warmth which will be generated by burning 1kg of the common cable insulations tabled. Certainly this heat will accelerate the burning of different adjoining materials and will help spread the fireplace in a building but importantly, in order to generate the heat power, oxygen must be consumed. The greater the heat of combustion the extra oxygen is needed, so by choosing insulations with excessive gasoline elements is adding significantly to a minimum of 4 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 metal conduits. This will certainly help flame unfold and minimize smoke as a outcome of inside the conduit oxygen is restricted; nonetheless this is not an answer. As mentioned beforehand, many of the gasses from the decomposing polymeric insulations contained in the conduits are highly flammable and poisonous. These gases will migrate along the conduits to junction bins, swap panels, distribution boards, motor control centers, lamps, switches, and so forth. 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 opposite toxic components of fire is a transparent admission we do not perceive the topic properly nor can we simply define the risks of mixed poisonous elements or human physiological response to them. It is important however, that we do not proceed to design with solely half an understanding of the issue. While no excellent answer exists for natural primarily based cables, we will definitely minimize these critically necessary effects of fireside danger:
One possibility maybe to choose on cable insulations and jacket materials which are halogen free and have a low gasoline element, then install them in steel conduit or maybe the American strategy is healthier: to use highly halogenated insulations so that in case of fireside any flame unfold is minimized.
For most energy, management, communication and data circuits there is one complete solution available for all the issues raised on this paper. It is a solution which has been used reliably for over eighty years. MICC cables can provide a total and full answer to all the issues related to the fireplace safety of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make sure the cable is effectively fire proof. MICC cables don’t have any natural content material so simply 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 can not generate any halogen or toxic gasses in any respect including CO.
Unfortunately many common cable hearth check methods used at present may inadvertently mislead individuals into believing the polymeric flexible cable merchandise they purchase and use will carry out as expected in all fireplace conditions. As outlined on this paper, sadly this is probably not correct.
For extra information, go to www.temperature-house.com
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