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Keep Functioning
Cable fires have often caused devastating disasters, from the destruction of a terminal at Düsseldorf Airport, to the crash of a Swissair flight five years ago. Wacker's new cable jackets can prevent such disasters. Safety cables keep functioning even at temperatures exceeding 1,000 °C because the silicone rubber jackets turn into protective ceramic layers. Hundreds of kilometers of such safety cable were installed at the newly opened Munich Airport terminal.
Smoldering or cable fires resulting from short circuits, which often spread unnoticed in hidden cable shafts, can lead to devastating disasters: the destruction of a Düsseldorf Airport terminal seven years ago is surely one of the most well-known fire disasters, but certainly not the only one caused by cable fires. That same year, namely 1996, such cable fires forced the Berlin subway to shut down three times. And in September 1998, a Swissair flight crashed into the ocean off the Canadian coast. The suspected cause was arcing between cables, whose insulation had become porous. And in August 2000, a smoldering cable in a transmitter booster caused a huge fire in Moscow's Ostankino television tower.
But the fact that cable fires can cause conflagration is only one of the key aspects. The question of how long electric cables can continue to function in the middle of a fire is almost even more important. After all, when still functional, cables guarantee that systems vital to survival also keep working. Thus, in the event of fires in subways or traffic tunnels, it is essential that the ventilation system operates as long as possible to remove smoke fumes. In the same way, extinguisher pumps, alarm systems, fire alarms, signaling devices, automatic door systems and elevators need to function long enough for people in the danger zone to escape or be rescued in the event of fires in buildings - whether in high-rises, hotels or airport terminals.
During such fires, temperatures can easily reach 800 to 1,000 °C or more. Then, even heat-resistant materials glow bright red and yellow, and at 1,083 °C even the copper in the wires begins to melt - how could cable jackets possibly withstand such an inferno? Previously, flame-resistant safety cables were expensive and complex custom-made products, for example covered with glass fabric mica tape. However, the cores of such special cables can only be taped at a rate of 10 to 15 meters a minute. They are difficult to handle, too.
These are all reasons why high-performance fire safety cables haven't previously found the widespread use they deserve. However, an invention by Wacker chemists is now blazing a trail toward revolutionizing this field. They developed a flame-resistant rubber grade which not only complies with all temperature requirements, but can also be processed into a core jacket up to 40 times more quickly. Safety cable manufacturers, such as Facab Lynen in the German state of North Rhine-Westphalia or the Belgian cable manufacturer Eupen, receive pellets made of this rubber from Wacker, which they can process in an extruder as a normal plastic. The pellet stock is fed to the extruder via a suction tube and is pressed through a die (similar to a pasta maker) which gives the rubber its cable jacket form. As this takes place at a very high speed, heat-resistant fire safety cables can be processed much more cost-efficiently than previously. Electricians are also pleased, because the new cables are almost as easy to handle as their cousins encased in conventional plastics. The development is based on a patent by Dr. Dietrich Wolfer, who invented a special formula for these silicone rubber grades. Silicones are made of a back bone composed of alternating silicon and oxygen atoms and can be provided with different organic side chains. Since 1947, Wacker Silicones has been manufacturing numerous types of products, such as oils, pastes, lipsticks, sealants and lubricants, resins and masonry protection agents and also, since just recently, special silicone rubber grades for safety cables under the Elastosil R.
At the very high temperatures experienced in fires, silicone rubber converts to carbon dioxide, water and silicon dioxide - which is nothing more than the substances composing sand, quartz and mica. The unique thing about the Wacker invention is that the silicon dioxide does not fall off the cable as ashes, but rather it continues to serve as a protective layer for electrical wiring. Thanks to this ceramic layer, the cable can also still conduct electricity in the event of a fire. Thus, this sets Wacker's fire safety cables apart from other plastic cable jackets. The latter are either consumed by the fire, triggering a short circuit resulting from unprotected copper wires - or they carbonize, e.g. form carbon. However, carbon is itself electrically conductive and thus causes short circuits, which leads to the collapse of electrical systems.
Wacker's silicone rubber safety cables comply with all major international norms, for example E90 according to DIN 4102, which requires the cable to remain functional for 90 minutes at temperatures up to 1,000 °C.
Even when subjected to the severest test for safety cables worldwide (UL 2196) performed by Underwriters Laboratories, an independent test institute in the USA, Wacker's Elastosil R502/75 rubber grade came through with flying colors.
In this test, the cables are exposed to the flames of 100 gas burners for two hours, during which a temperature of almost 1,100 °C is reached. Then, the test technicians spray the incandescent cables with high-pressure water from a fire hose. The whole time, connected light bulbs must not go out.
Customers increasingly appreciate these advantages. Wacker's annual production quantities are already in the three-figure ton area. Thus, Wacker rubber grades were used in constructing the new Düsseldorf airport terminal, projects at the renowned American universities Harvard and MIT in Boston, and new hotels for the Marriott chain in the USA. The safety cables were predominantly selected for maximum functioning time of ventilation ducts for removal of smoke fumes and for escalators, fire alarms, signaling devices and extinguisher pumps during fires. However, suppliers for trains and subways are also increasingly turning to the new fire safety cables.
And they can be found everywhere in one of the largest transportation construction projects around: Munich Airport's newly opened Terminal 2, built at a cost of EUR 1.3 billion. In the future, up to 25 million passengers will pass through its gates annually. For safety, hundreds of kilometers of cables are equipped with dozens of tons of Wacker silicone rubber jackets. The most impressive example is the baggage conveyor system built by Siemens. The conveyor belts, which can transport up to 100,000 pieces of luggage per day, are 40 kilometers long and powered by 19,000 electric motors. All signal cables are designed as fire safety cables using Wacker silicone rubber grades. The reason for this is simple. After all, the baggage conveyor system should keep functioning until all luggage and bags, which are, of course, easily flammable, can be removed from the danger zone - plus the cables should retard the fire from spreading, ensuring that all fire doors are shut in time.
The following grades belong to this line of products:
But the fact that cable fires can cause conflagration is only one of the key aspects. The question of how long electric cables can continue to function in the middle of a fire is almost even more important. After all, when still functional, cables guarantee that systems vital to survival also keep working. Thus, in the event of fires in subways or traffic tunnels, it is essential that the ventilation system operates as long as possible to remove smoke fumes. In the same way, extinguisher pumps, alarm systems, fire alarms, signaling devices, automatic door systems and elevators need to function long enough for people in the danger zone to escape or be rescued in the event of fires in buildings - whether in high-rises, hotels or airport terminals.
During such fires, temperatures can easily reach 800 to 1,000 °C or more. Then, even heat-resistant materials glow bright red and yellow, and at 1,083 °C even the copper in the wires begins to melt - how could cable jackets possibly withstand such an inferno? Previously, flame-resistant safety cables were expensive and complex custom-made products, for example covered with glass fabric mica tape. However, the cores of such special cables can only be taped at a rate of 10 to 15 meters a minute. They are difficult to handle, too.
These are all reasons why high-performance fire safety cables haven't previously found the widespread use they deserve. However, an invention by Wacker chemists is now blazing a trail toward revolutionizing this field. They developed a flame-resistant rubber grade which not only complies with all temperature requirements, but can also be processed into a core jacket up to 40 times more quickly. Safety cable manufacturers, such as Facab Lynen in the German state of North Rhine-Westphalia or the Belgian cable manufacturer Eupen, receive pellets made of this rubber from Wacker, which they can process in an extruder as a normal plastic. The pellet stock is fed to the extruder via a suction tube and is pressed through a die (similar to a pasta maker) which gives the rubber its cable jacket form. As this takes place at a very high speed, heat-resistant fire safety cables can be processed much more cost-efficiently than previously. Electricians are also pleased, because the new cables are almost as easy to handle as their cousins encased in conventional plastics. The development is based on a patent by Dr. Dietrich Wolfer, who invented a special formula for these silicone rubber grades. Silicones are made of a back bone composed of alternating silicon and oxygen atoms and can be provided with different organic side chains. Since 1947, Wacker Silicones has been manufacturing numerous types of products, such as oils, pastes, lipsticks, sealants and lubricants, resins and masonry protection agents and also, since just recently, special silicone rubber grades for safety cables under the Elastosil R.
At the very high temperatures experienced in fires, silicone rubber converts to carbon dioxide, water and silicon dioxide - which is nothing more than the substances composing sand, quartz and mica. The unique thing about the Wacker invention is that the silicon dioxide does not fall off the cable as ashes, but rather it continues to serve as a protective layer for electrical wiring. Thanks to this ceramic layer, the cable can also still conduct electricity in the event of a fire. Thus, this sets Wacker's fire safety cables apart from other plastic cable jackets. The latter are either consumed by the fire, triggering a short circuit resulting from unprotected copper wires - or they carbonize, e.g. form carbon. However, carbon is itself electrically conductive and thus causes short circuits, which leads to the collapse of electrical systems.
Wacker's silicone rubber safety cables comply with all major international norms, for example E90 according to DIN 4102, which requires the cable to remain functional for 90 minutes at temperatures up to 1,000 °C.
Even when subjected to the severest test for safety cables worldwide (UL 2196) performed by Underwriters Laboratories, an independent test institute in the USA, Wacker's Elastosil R502/75 rubber grade came through with flying colors.
In this test, the cables are exposed to the flames of 100 gas burners for two hours, during which a temperature of almost 1,100 °C is reached. Then, the test technicians spray the incandescent cables with high-pressure water from a fire hose. The whole time, connected light bulbs must not go out.
Customers increasingly appreciate these advantages. Wacker's annual production quantities are already in the three-figure ton area. Thus, Wacker rubber grades were used in constructing the new Düsseldorf airport terminal, projects at the renowned American universities Harvard and MIT in Boston, and new hotels for the Marriott chain in the USA. The safety cables were predominantly selected for maximum functioning time of ventilation ducts for removal of smoke fumes and for escalators, fire alarms, signaling devices and extinguisher pumps during fires. However, suppliers for trains and subways are also increasingly turning to the new fire safety cables.
And they can be found everywhere in one of the largest transportation construction projects around: Munich Airport's newly opened Terminal 2, built at a cost of EUR 1.3 billion. In the future, up to 25 million passengers will pass through its gates annually. For safety, hundreds of kilometers of cables are equipped with dozens of tons of Wacker silicone rubber jackets. The most impressive example is the baggage conveyor system built by Siemens. The conveyor belts, which can transport up to 100,000 pieces of luggage per day, are 40 kilometers long and powered by 19,000 electric motors. All signal cables are designed as fire safety cables using Wacker silicone rubber grades. The reason for this is simple. After all, the baggage conveyor system should keep functioning until all luggage and bags, which are, of course, easily flammable, can be removed from the danger zone - plus the cables should retard the fire from spreading, ensuring that all fire doors are shut in time.
Background Information
Wacker produces different types of highly elastic, 3D-vulcanized silicone rubber grades, which all convert to a hard and conductive protective ceramic layer around the cables.The following grades belong to this line of products:
- Elastosil R 502/75: enables cables to keep functioning up to about 950 °C
- Elastosil R 503/75: remains functional up to about 1100 °C
- Elastosil R 543/70: consists of two components and keeps functioning up to about 1,000 °C
- These materials are available as clear or colored pellets, but also as silicone foams
- chiefly used in the inner jackets of cables and in sealing profiles for fire doors.
The silicone rubber grades:
- Comply with all major international fire norms, for example German DIN 4102 Part 12 (E30, -60, -90) or the American UL 2196
- Produce only small amounts of smoke and no corrosive or toxic combustion products
- Have excellent processing characteristics
- Are very stabile and long-lasting under normal usage
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