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Too hot to handle
July 22, 2015 – It’s just another routine flight cruising over the Atlantic at 35,000ft. In the quiet cabin, passengers are working on their laptop computers and some are charging their smartphones.
Suddenly, there’s a whiff of pungent smoke followed by a ‘pop’ as one of the laptops erupts with a wave of noxious smoke and toxic fumes. The smoke and fumes begin to quickly disperse throughout the aircraft, and passengers start to panic. Within about a minute, the laptop bursts into flames. You are now faced with a runaway Lithium-Ion (Li-ion) battery fire and have no options for landing.
Sound far-fetched? Think again. From March 1991 to October 2014, the FAA Office of Security and Hazardous Materials Safety recorded 144 cases of aviation incidents involving smoke, fire, extreme heat or explosion involving batteries and battery-powered devices, with more than half of those incidents occurring in the past five years.
Just this past April, there were two incidents of laptops emitting smoke onboard commercial flights, one of which had to be diverted. Also in April, Lenovo recalled the battery packs for its Think Pad Notebooks due to fire hazard concerns. On June 3, 2015, Apple recalled 220,000 of its Beats Pill XL speakers because, according to the company, “Apple has determined that, in rare cases, the battery in the Beats Pill XL Speaker may overheat and pose a fire safety risk.”
As the number of PEDs that passengers carry multiplies (laptop computers, smartphones, tablet PCs, e-readers, MP3 players, e-cigarettes, etc), lithium batteries present an increasing risk of inflight fire. The airline industry recently estimated that the typical passenger brings an average of 4.5 Li- ion cells onto each flight (a typical smartphone contains one Li-ion cell; a tablet PC or e-reader has two cells; and a laptop computer contains 6-10 cells.)
While Li-ion batteries are very useful as a power source for PEDs, they can become quite dangerous if they go into thermal runaway. Thermal runaway occurs when a change in the temperature of a battery alters conditions in such a way that causes the internal temperature to continue to rise on its own. The heat from a cell in thermal runaway can then cause the other cells in the battery pack to heat up as well. For a Li-ion battery, with its flammable organic electrolyte, thermal runaway usually results in ruptured cells and a fire.
There are three basic reasons why a Li-ion battery cell will go into thermal runaway:
• Manufacturing defects
• Damaged cells
• Overheated cells
Li-ion cell manufacturers report a manufacturing defect rate per cell of 1:10 million. This sounds like a small amount, but with the potential of several hundred cells being carried onboard every commercial aircraft, the probability of a defect-related fire can quickly drop below 1:50,000.
The probability of thermal runaway being caused by a damaged cell is more difficult to predict, but it may occur because a PED is accidentally dropped or crushed, causing a short circuit in the battery, which in turn causes internal heating. For example, a fire recently occurred on board an aircraft when a tablet PC was crushed after sliding into the reclining mechanism of a first class cabin seat.
The third and more insidious reason for thermal runaway is related to direct overheating. Testing shows that overheating a PED will produce a thermal runaway condition 99% of the time, even in perfectly good Li-ion cells and batteries.
Great care must be taken not to overheat a PED at any time. Some not so obvious ways to overheat a PED include (but are not limited to):
• Charging any PED without adequate air circulation, such as in a briefcase, in its protective case, or in an airplane seat pocket
• Using or charging a laptop computer on carpet or fabric. These fabrics may block the fan ports of the laptop that are designed to cool the computer and its battery
• Leaving the PED in a hot environment (in a car or in direct sunlight for example)
Toxic and flammable fumes
A Li-ion battery in thermal runaway within the close confines of an aircraft cabin is dangerous not only because of the flames and heat generated by the burning device, but also because a battery fire produces:
• Toxic organic vapors, which are also flammable
• Noxious smoke from burning plastic, which may also produce cyanide
• Other extremely unpleasant odors that can infiltrate the seats, carpets, etc
All of these fumes and vapors are irritating to the eyes and lungs, and they can circulate quickly throughout the aircraft cabin via the highly efficient ventilation system. As thermal runaway progresses, the emission of organic electrolyte vapors climbs dramatically, along with the battery temperature.
Fighting the fire
What is the best way to handle such an inflight emergency? A Li-ion battery in ‘thermal runaway’ is a very special fire. In Li-ion batteries, thermal runaway is manifested in the form of rapidly increasing cell temperatures (~1,000°F), and the violent rupturing and burning of cells, one after another in a cascading manner. Conventional fire suppressants that serve to ‘smother’ a fire will not work on a battery fire.
The halon and water method is unsafe and unpredictable. By this method, a halon fire extinguisher is first used to bring the flames related to the burning plastic and spewing solvent under control, but this does nothing to control the thermal runaway condition of the Li-ion battery and the battery fire is still burning within the PED. Once thermal runaway has started, tremendous heat is generated at the Li-ion cell level, even after the visible flames are extinguished.
The second step in the halon and water method is to pour water on to the device in an attempt to cool the battery and thus stop the thermal runaway process. But how much water is enough to make sure the thermal runaway is stopped? In controlled testing, it has been shown that as much as five liters (approximately 1.5 gallons) of water does not fully contain the thermal runaway taking place within a burning device.
The fact is that today’s computer keyboards are designed to be spill-proof, and pouring water onto a keyboard does little to abate the thermal runaway. The Li-ion battery pack is typically buried deep in the laptop computer, thus making water ingress all but impossible. Therefore, the fire may start-up again. There is no safe, predictable method currently being used, that allows the flight crew to know for certain that the device is cooled to the point that the thermal runaway is controlled, unless the device is totally submerged in water.
The chart below is an actual temperature data log recording of a laptop computer that was induced into thermal runaway under controlled conditions by placing a cartridge heater in the battery pack. It shows that after the heater is turned on (Point 1), the pack temperature increases slowly and steadily until the temperature in the battery pack reaches approximately 100°C (212°F). At this time, the battery goes into thermal runaway, and the temperature skyrockets.
Points 2 and 3 show where two cells in the Li-ion battery pack rupture in quick succession as the heater is turned off (Point 4). At Point 5 the first bottle of water (1.5 liters, 0.40 gallons) is poured on to the keyboard of the computer. The temperature begins to drop, and a second bottle of water (1.5 liters, 0.40 gallons) is poured onto the keyboard (Point 6). The temperature drops again in response to the second bottle. If this were taking place on an airplane, a flight crew might think the fire was safely contained and would be considering how to safely handle the still very warm computer (275°C/527°F).
But, as the chart shows, the 3 liters of water have not controlled the thermal runaway. Within about one minute, the temperature of the battery pack begins to escalate again, and a third cell ruptures (Point 7). Here additional water is poured on the keyboard (Point 8) to further attempt to cool the PED. Even at this point, the flight crew would have no way to determine if their actions have been successful. For the purposes of this test, the computer was finally immersed in a bucket of water (Point 9) to completely cool the battery pack and stop the thermal runaway process.
The halon and water method is not a total containment and control procedure. This method also does not contain or control the noxious smoke and odor that is emitted by a burning device. As can be seen from the photograph below, there is a tremendous amount of organic electrolyte vapor released at the onset of thermal runaway. This is not smoke; it is vaporized electrolyte, which is an ether-based solvent.
This organic vapor is not only irritating to the eyes and lungs, etc but is also flammable, and as shown in photograph 2, can quickly produce a violent fire.
The combination of burning plastic and the burning electrolyte produce toxic vapors and a very unpleasant odor, which are quickly circulated throughout the entire aircraft cabin.
If a Li-ion fire is not properly contained and controlled, the aircraft will need to be diverted as soon as possible, as there is always a chance the fire will re-start even if it seems to be out. With this method, one is never quite certain if the fire is out completely.
So what can be done to safely address the risks of a PED fire?
The Royal Aeronautical Society’s ‘Smoke, Fire and Fumes In Transport Aircraft’ (SAFITA) guidelines, third edition, 2014, states: “Technologies are available that are able to contain portable electronic devices which are actively involved in a lithium-ion battery failure. While there have been several of these containment devices on the market, few have featured both adequate protection for the person attempting to contain the device and a method for suppressing a fire after containment. New technology now can protect the person moving the device and contain it safely. Incorporation of this technology is recommended in passenger aeroplanes... Thermal containment technology is available and should be considered for carriage in the cabin by all operators.”
HighWater Innovations developed the PlaneGard capture and containment device with a view to solving the risks of Li-ion batteries in aircraft cabins. The case allows flight crew to handle a smoking or burning PED without personal contact, and key to the design is the ‘Scoop’, which can shield the firefighter as s/he approaches the burning device and which can also be used to close the lid of the laptop. Once closed, the Scoop also allows the user to drop the device into the case in one quick motion, where it is sealed, to contain any danger of flames, heat, toxic vapors or smoke. Even if the device goes into thermal runaway inside the case, the insulation inside the case, which is similar to space shuttle tile, keeps the outside of the case cool to the touch, and all toxic fumes are filtered, protecting passengers and the aircraft interior. After the device is physically contained in the case, water can then be introduced through the lid to totally submerge the device and completely extinguish the burning battery.
A thermal runaway situation is unpredictable, and no two battery packs behave the same way. In our controlled testing we have seen battery packs that create a small amount of toxic vapor and smoke and not much else, while others immediately burst into flames, spewing hot plastic and metal into the air as each cell ruptures. We have also seen battery packs that go from a very small amount of smoke, to flames and an actual explosion in a very short time. This unpredictability is a prime reason that any PED needs to be captured and contained at the first sign of smoke or overheating, rather than sitting in the open with water being poured on it by an unprotected flight attendant. We believe aircraft operators need a safe, reliable method to contain and control a Li-ion fire event, which removes ambiguity and adds safety and confidence.
Further information and videos of the device being used are available at www.highwaterinnovations.com
22 July 2015
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