Life Safety and Fire Fighting Systems – The weakest link

Unlike other cables, hearth resistant cables should work even when instantly exposed to the fire to keep essential Life Safety and Fire Fighting gear working: Fire alarms, Emergency Lighting, Emergency Communication, Fire Sprinkler pumps, Fireman’s Lift sub-main, Smoke extraction followers, Smoke dampers, Stair pressurization fans, Emergency Generator circuits and so forth.
In order to classify electric cables as hearth resistant they are required to undergo testing and certification. Perhaps the first widespread hearth checks on cables had been IEC 331: 1970 and later BS6387:1983 which adopted a fuel ribbon burner take a look at to produce a flame during which cables have been positioned.
Since the revision of BS6387 in 1994 there have been eleven enhancements, revisions or new check standards launched by British Standards for use and software of Fire Resistant cables but none of those seem to handle the core concern that fireside resistant cables where examined to common British and IEC flame check standards are not required to perform to the identical hearth performance time-temperature profiles as each different construction, system or element in a constructing. Specifically, the place hearth resistant constructions, systems, partitions, fireplace doors, fireplace penetrations fire limitations, floors, partitions etc. are required to be hearth rated by building regulations, they’re tested to the Standard Time Temperature protocol of BS476 parts 20 to 23 (also known as ISO834-1, ASNZS1530pt4, EN1363-1 and in America and Canada ASTM E119-75).
These exams are performed in giant furnaces to replicate real publish flashover fireplace environments. Interestingly, Fire Resistant cable test standards like BS 6387CWZ, SS299, IEC 60331 BS8343-1 and 2, BS8491 only require cables to be exposed to a flame in air and to lower final check temperatures (than required by BS476 pts 20 to 23). Given Fire Resistant cables are likely to be uncovered in the same fire, and are needed to ensure all Life Safety and Fire Fighting systems remain operational, this fact is perhaps shocking.
Contrastingly in Germany, Belgium, Australia, New Zealand, USA and Canada Fire Resistant cable techniques are required to be examined to the identical fire Time Temperature protocol as all other building parts and this is the Standard Time Temperature protocol to BS476pts 20-23, IS0 834-1, EN1363-1 or ASTM E119-75 in USA.
The committees creating the usual drew on the guidance given from the International Fire Prevention Congress held in London in July 1903 and the measurements of furnace temperatures made in lots of fireplace checks carried out in the UK, Germany and the United States. The tests have been described in a series of “Red Books” issued by the British Fire Prevention Committee after 1903 as well as these from the German Royal Technical Research Laboratory. The finalization of the ASTM normal was heavily influenced by Professor I.H. Woolson, a Consulting Engineer of the USA National Board of Fire Underwriters and Chairman of the NFPA committee in Fire Resistive Construction who had carried out many checks at Columbia University and Underwriters Laboratories in Chicago. The small time temperature differences between the International ISO 834-1 test as we know it right now and the America ASTM E119 / NFPA 251 checks doubtless stemmed from this time.
Image courtesy of MICC Ltd.
The curve as we see it at present (see graph above) has turn into the standard scale for measurement of fireside take a look at severity and has proved related for most above floor cellulosic buildings. When components, structures, components or techniques are tested, the furnace temperatures are controlled to conform to the curve with a set allowable variance and consideration for initial ambient temperatures. The requirements require elements to be examined in full scale and underneath circumstances of support and loading as outlined in order to symbolize as accurately as attainable its features in service.
This Standard Time Temperature testing protocol (see graph right) is adopted by virtually all countries around the world for fire testing and certification of just about all building constructions, elements, techniques and components with the interesting exception of fireside resistant cables (exception in USA, Canada, Australia, Germany, Belgium and New Zealand the place fire resistant cable systems are required to be tested and approved to the Standard Time Temperature protocol, similar to all different building constructions, elements and components).
It is important to grasp that utility standards from BS, IEC, ASNZS, DIN, UL and so forth. the place fireplace resistive cables are specified for use, are solely ‘minimum’ requirements. We know at present that fires aren’t all the same and research by Universities, Institutions and Authorities around the world have recognized that Underground and some Industrial environments can exhibit very totally different fire profiles to these in above ground cellulosic buildings. Specifically in confined underground public areas like Road and Rail Tunnels, Underground Shopping centers, Car Parks fire temperatures can exhibit a really quick rise time and can reach temperatures nicely above those in above ground buildings and in far much less time. In USA at present electrical wiring methods are required by NFPA 502 (Road Tunnels, Bridges and different Limited Access Highways) to resist fireplace temperatures as a lot as 1,350 Degrees C for 60 minutes and UK British Standard BS8519:2010 clearly identifies underground public areas such as automobile parks as “Areas of Special Risk” the place extra stringent test protocols for important electrical cable circuits might need to be considered by designers.
Standard Time Temperature curves (Europe and America) plotted against common BS and IEC cable tests.
Of course all underground environments whether or not road, rail and pedestrian tunnels, or underground public environments like buying precincts, car parks and so forth. could exhibit totally different fireplace profiles to those in above floor buildings because In these environments the heat generated by any hearth can not escape as easily as it’d in above ground buildings thus relying more on heat and smoke extraction equipment.
For Metros Road and Rail Tunnels, Hospitals, Health care facilities, Underground public environments like purchasing precincts, Very High Rise, Theaters, Public Halls, Government buildings, Airports and so forth. this is particularly important. Evacuation of those public environments is usually slow even during emergencies, and it’s our responsibility to make sure everyone is given the easiest chance of protected egress throughout hearth emergencies.
It is also understood at present that copper Fire Resistant cables the place installed in galvanized metal conduit can fail prematurely throughout hearth emergency due to a response between the copper conductors and zinc galvanizing inside the steel conduit. In 2012 United Laboratories (UL®) in America eliminated all certification for Fire Resistive cables where installed in galvanized metal conduit because of this:
UL® Quote: “A concern was dropped at our consideration associated to the performance of those products in the presence of zinc. We validated this finding. As a results of this, we changed our Guide Information to indicate that each one conduit and conduit fittings that are available contact with hearth resistive cables should have an interior coating freed from zinc”.
Time temperature profile of tunnel fires using vehicles, HGV trailers with completely different cargo and rail carriages. Graph extract: Haukur Ingason and Anders Lonnermark of the Swedish National Testing and Research Institute who offered the paper at the First International Symposium in Prague 2004: Safe and Reliable Tunnels.
It would seem that some Standards authorities all over the world may have to review the current check methodology currently adopted for hearth resistive cable testing and perhaps align the efficiency of Life Safety and Fire Fighting wiring methods with that of all the other fire resistant constructions, components and systems in order that Architects, building designers and engineers know that once they need a fireplace rating that the essential wiring system will be equally rated.
For many energy, control, communication and information circuits there is one know-how obtainable which can meet and surpass all present fireplace tests and applications. It is a solution which is incessantly used in demanding public buildings and has been employed reliably for over eighty years. MICC cable expertise can provide a complete and full reply to all the problems related to the fireplace safety dangers of modern flexible natural polymer cables.
The metal jacket, magnesium oxide insulation and conductors of MICC cables make positive the cable is successfully hearth proof. Bare MICC cables have no natural content material so merely can not propagate flame or generate any smoke. The zero fuel-load of these MICC cables ensures no heat is added to the hearth and no oxygen is consumed. Being inorganic these MICC cables cannot generate any halogen or poisonous gasses in any respect together with Carbon Monoxide. MICC cable designs can meet the entire present and building fireplace resistance efficiency requirements in all countries and are seeing a big increase in use globally.
Many engineers have previously considered MICC cable technology to be “old school’ but with the new research in fire efficiency MICC cable system at the second are proven to have far superior hearth performances than any of the newer more trendy flexible fireplace resistant cables.
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