Monday, July 26, 2004
Lithium Battery Fire Could Burn Through a Cargo Hold
Halon extinguishing agent has no effect on fire intensity
Lithium batteries may represent the ultimate hazardous material, especially when shipped in bulk as cargo, with the potential to breach all defenses should they catch fire. That is the principal finding of a June report of lithium battery fire tests conducted by the Federal Aviation Administration (FAA) Technical Center at Atlantic City, N.J.
The extreme hazard portrayed in the report suggests that it may be time to consider restricting lithium battery shipments to cargo aircraft. Presently, lithium battery shipments require prominent labeling as hazardous cargo, and, after Jan. 1, 2005, the batteries must undergo a "battery" of tests in order to be approved for shipment. However, those tests - for altitude, vibration, shock, etc. - do not include a test for fire resistance. In a shipment of closely packed lithium batteries, should one battery catch fire, a chain reaction results. The fire spreads from battery to battery in an explosive conflagration of molten lithium, according to the Technical Center report.
The examination of lithium battery fires was undertaken after a pallet of such batteries caught fire on the ground at Los Angeles International Airport in April 1999. The pallet was inadvertently dropped onto the tarmac, and a battery fire resulted, despite there being no external ignition source. There are no confirmed reports of bulk lithium battery fires in the air, but that is precisely the reason the FAA Tech Center undertook its examination of this more dangerous scenario. There is one case where a lithium battery fire may have played a role in the crash of a transport category airplane. In November 1987 a South African Airways B747 combi (a hybrid freighter with a partition separating cargo from passengers on the main deck), with 159 passengers aboard and cargo which included a consignment of lithium watch batteries, disappeared into the Indian Ocean off Mauritius.
After a wreck survey by robot cameras and limited debris recovery, investigators determined that the lithium batteries were located in the same area that was established to have been the seat of the fire. The airplane also was carrying a cargo of ammonium perchlorate, a rocket propellant known to be unstable and capable of spontaneous ignition. As a propellant with its own oxygen, ammonium perchlorate would have rapidly promoted a fire. However, in revealing testimony to the South African Truth and Reconciliation Commission, the presence of the lithium battery shipment was mentioned, and is pertinent to what has been revealed by the FAA lithium fire tests about battery venting, explosions, and accelerated self-reactive fires. The testimony obviously was dealing with the batteries' packaging material, but the general description of the fire that doomed the plane reinforces the point that lithium batteries can be extremely dangerous if they catch fire.
Using a steel test chamber to simulate an aircraft cargo hold, the FAA tests show that a runaway fire involving a shipment of lithium batteries might well result in loss of the aircraft. The batteries involved were those used commonly in consumer electronic products (e.g., video cameras).
Batteries were tested singly, and in groups of 32, 64 and 128. Tests also involved groups of batteries packed in rows inside cardboard boxes.
For test purposes, the battery fires were started by igniting a "fire pan" filled with alcohol. The findings were fearful. To summarize:
- A relatively small fire source was sufficient to start a lithium battery fire.
- The heat from a single battery afire was sufficient to ignite adjacent batteries.
- The outer plastic coating on the batteries easily melted, fusing the batteries together, adding to the intensity of the fire.
- The chain reaction ignition continued until all batteries were consumed.
- The molten lithium burned explosively, spraying white-hot lithium to a radius of several feet as the batteries bounced around.
- The duration of the peak temperature increased with the number of batteries, reaching as high as 1,400� F (as a matter of interest, the melting temperature of aluminum is around 1,200� F).
- The cardboard packing proved highly flammable. The packing delayed battery ignition by about 30-60 seconds, but once ignited, the fire among the close-packed batteries was worse.
- While thick-wall cargo liners were able to contain the fire (barely), thin-walled fire liners proved ineffective. The battery fire ignited the resin in the liner, and the liner was completely penetrated by molten lithium.
- Halon fire-suppressing agent, injected in sufficient concentration to "knock down" a fire, proved totally ineffective, even when injected after just the first battery had caught fire. Nor did it have any effect on the peak temperature. The fire continued as if Halon were not present.
- Lithium batteries catch fire with explosive force. When they burst, they create a pressure pulse. The eight-battery test produced a pressure pulse of 1.8 psi, and the 16- battery test generated a 2.6 psi pulse.
According to the Tech Center report:
"These results are significant. The cargo compartment is only constructed to withstand a 1-psi pressure differential in order to rapidly equalize the pressure in the event of a depressurization. Anything over 1 psi would activate the blowout panels, compromising the cargo compartment's [fire-resistant] integrity."
The effect is the same as perforating the cargo liner.
- A cargo bay fire from a totally unrelated source can cause a shipment of lithium batteries to ignite. Tech Center investigators found that the temperatures found in a suppressed smoldering cargo fire are sufficient to ignite a lithium battery.
Add one other factor - the butane used as propellant in personal care products packed into passengers' bags - and put it all together: A cargo fire of unknown origin starts and ignites a shipment of lithium batteries. With a cargo bay fire warning in the cockpit, the pilots discharge Halon, with no effect. The molten fireworks of lithium burns through the cargo liner, and penetrates the aluminum skin of the cargo bay. The holes allow for an inrush of air, adding oxygen to the fire. The exploding batteries create sufficient overpressure to punch out the blowout panels - allowing for more inrush of oxygen and spread of the fire outside the hold. The heat rise is sufficient to cause aerosol cans of shaving cream, hairspray, etc., to burst. Earlier tests have demonstrated that a single such can, placed in a bag located near the ceiling, can explode with sufficient force to distort and heave up the cabin floor.
Although they must be marked as hazardous cargo, there presently is no limit on the number of lithium batteries that can be shipped on a commercial aircraft.
There are two obvious implications of this scenario. First, ETOPS (extended range operations) is based on the presumption that a belly-hold fire can be suppressed by Halon for three hours. It does not account for the catastrophic progression of a pallet of lithium batteries catching fire. Such a fire would easily burn its way through current defenses.
The danger is such that a terrorist would not need to use explosives that could be detected in his checked or hand luggage by an explosives detection system (EDS). A lithium fire would create havoc enough. This scenario supports the need, as a minimum, for positive passenger bag-match (PPBM) for domestic flights as well as the current requirement for international flights (see ASW, Nov. 12, 2001).
There is one bit of final irony to this tale: the smoke detector units of some aircraft fire detection systems are powered by lithium batteries.
(The full report, "Flammability Assessment of Bulk-Packed, Nonrechargeable Lithium Primary Batteries in Transport Category Aircraft," Report No. DOT/FAA/AR-04/26, may be viewed at http://www.fire.tc.faa.gov/pdf/04-26.pdf. The UK Civil Aviation Authority produced a report in July 2003 in which Halon was found effective for suppression of single-battery lithium fires, although in these cases the batteries were contained in their electronic devices. For this report, see http://www.caa.co.uk/publications/publicationdetails.asp?id=985)