2014

Layered Approach
FedEx has worked towards a layered approach to the transportation of
Lithium metal and Lithium-ion cells and batteries.
One layer is to suppress a fire within a Unit Load Device (ULD). This is accomplished with the Fire Suppression System (FSS) mounted onboard the aircraft.
Another layer is to develop packaging that will prevent the spread of a thermal runaway from one cell or battery to an adjacent cell or battery with in a package.
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FedEx’s Fire Suppression System
Both the active FSS, using cargo foam, and the passive system with a Fire
Containment Cover (FCC), has been tested with equipment containing lithium-ion batteries and packages of bulk lithium primary cells.
FedEx’s Onboard FSS
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FedEx’s FCC
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Transportation of Equipment Containing Lithium-ion Batteries
The FSS can suppress a fire in which equipment containing lithium-ion batteries are present.
A 192 laptops packaged and loaded in an AMJ per standard operating procedures were set on fire. The laptop batteries had a 50% state of charge. The FSS successfully contained and extinguished the fire.
Loading prior to test
Note: Additional laptops were not used due to crushing
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Four hours after ignition
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Transportation of Equipment Containing Lithium-ion Batteries
A 194 laptops packaged and loaded on a pallet per standard operating procedures were covered with a FCC and set on fire.
The laptop batteries had a 50% state of charge. The FCC successfully contained the fire for four hours.
Prior to ignition
Note: Additional laptops were not used due to crushing
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Four hours after ignition
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Transportation of Bulk Packaged Lithium Metal Cells
A full scale live fire test consisting of a standard fire load in an AMJ with a single layered tray consisting of a quantity of 100 CR123 lithium primary cells inserted into the fire load. The lithium cells were used as the ignition source. The FSS successfully contained and extinguished the fire.
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Transportation of Bulk Packaged Lithium Metal Cells
A full scale live fire test was conducted consisting of a standard fire load on a pallet with a single layered tray consisting of a quantity of 100
CR123 lithium primary cells inserted into the fire load. Again the lithium cells were used as the ignition source. A FCC was placed over the fire load.
The cells created several small holes in the FCC. However flames from the remainder of the fire load did not exit the FCC.
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Transportation of Bulk Packaged Lithium Metal Cells
The spread of thermal runaways was not halted when cargo foam flowed over a box containing multiple layers of cells.
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FAA Testing
ULD
30 gallon steel drum.
Main Deck Cockpit Door
The U.S. Federal Aviation Administration’s testing has shown that extinguishing the flames and controlling the heat will not keep the aircraft safe when a bulk shipment of lithium batteries is experiencing thermal runaways. The explosive gases must also be controlled.
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Bulk Packaging – Strategy
FedEx has researched ways of controlling the heat and suppressing the flames when a bulk shipment of Lithium cells go into thermal runaway, however containing the large quantity of flammable and explosive gas that will be vented was believed to be economically infeasible to contain.
Equipment designed to contain the flames and the heat while venting the flammable gases over board has been discussed. In fact Boeing dealt with a thermal runaway issue on the 787 by separating the cells with ceramic insulation, encasing the battery in a steel box and venting the exhaust gases overboard.
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Bulk Packaging – Strategy
There is no known way of preventing the first cell from going into thermal runaway.
However a single cell experiencing a thermal runaway will not significantly endanger the aircraft.
The unhindered cascading spread of the thermal runaway from cell to cell in a bulk shipment will create sufficient hazards to endanger the flight crew and the aircraft.
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Bulk Packaging – Strategy
This provided three benefits:
1.
It eliminated the flames or reduced the flames to an intensity level which current techniques will suppress.
2.
It assures that any heat generated would not cause damage to surrounding packages; including structural damage to the aircraft.
3.
It eliminates the possibility of the flammable gases that are released from reaching an explosive level.
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Bulk Packaging – Initial Testing
FedEx first tried to thermally isolate one cell from adjacent cells.
This proved difficult.
Several materials and configurations worked.
However they were bulky, cumbersome, and significantly increased the weight and cost of the packaging.
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Bulk Packaging – Change of Strategy
An alternative to thermally isolating each cell is to cool the cell experiencing the thermal event to a temperature that would not adversely affect the surrounding cells.
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Bulk Packaging – Cooling Concept
Liquid Cooling Concept:
• A pouch containing a liquid coolant is placed above the cells.
• When a cell experiences a thermal event, the heat from the cell ruptures the pouch thereby releasing the coolant.
• The coolant flowing over and around the cells decreases the temperature and prevents other cells from experiencing temperatures that would cause additional thermal runaways.
Only the cell forced into thermal runaway vented
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Bulk Packaging - Refinements
Modifications to the existing bulk packaging to optimize the cooling concept are required.
The liquid coolant has a tendency to soak into any absorbent material, i.e. cardboard. Therefore the cells have been placed in a coated tray in order to retain the fluid.
A buffer was required between the cells and the gel pack. Without a buffer the liquid in the gel pack would start to boil before the pouch ruptured.
Thereby cooling the top of the cell and allowing the bottom of the cell to continue to heat and vent out the side.
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Bulk Packaging
The gel packs will have to be placed with in the packaging on top of each layer of cells, therefore the battery manufacturers will have to adopt this packaging in lieu of their current configuration.
The exhaust gases are diluted with nonflammable water vapor.
Testing was performed to determine the fluid composition, viscosity, and release rate. It was determined that a mixture of liquid and gel provided the proper saturation and dwell of the cooling agent on the cells.
The modifications will increase the weight of each shipment by 12% to
18% and increase the volume by 20% to 40%, depending on the battery geometry.
The gel packs are non-toxic and may be disposed of after a single use or they can be reused until they are damaged.
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Bulk Packaging – Results
Burn testing has been successfully performed on CR123 lithium primary,
18650 lithium-ion (typically found in laptops) and “D” size lithium primary cells.
CR123
18650
Thermal Events -
Sparks and Flames blow through box
33550
D size
Gel Packs prevented jets of sparks and flames from exiting the box. Only the cell experiencing the thermal runaway vented.
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Bulk Packaging – Large Scale Tests
CR123 Lithium Primary
99 Per Box w/ Gel Packs
Two Boxes Per Carton
Only One Cell Vented
33550 Lithium Primary
25 Per Box w/ Gel Packs
Four Boxes Per Carton
Only One Cell Vented
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Bulk Packaging – Multi Cell Battery Tests
Three “D” size Lithium primary cells with electronics encased in rigid plastic
Multiple Gel Pack designs and packaging configurations have been tested. Several configurations prevented the spread of the thermal runaway in a multi-cell Lithium metal battery. A few configurations prevented flames from escaping the packaging.
Packaging orientation prevented the spread of the thermal runaway.
Only one cell vented .
Nine batteries with Gel packs lining the side walls and top.
The venting gases started a fire on the outside of the packaging. The Gel Packs stopped the fire from reaching the batteries.
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Conclusions
The “Layered” approach works for containing thermal events involving Lithium-ion and Lithium metal cells and batteries.
FedEx’s Fire Suppression System, both the active foam and the fire containment cover, have been proven to suppress both a fire in which equipment containing Lithium-Ion batteries were involved and a fire with a limited quantity of small Lithium metal batteries.
The Gel Packs have been proven to stop the spread of a thermal runaway in a bulk shipment of Lithium metal or Lithium-ion cells.
Development will be required for each type of battery or battery pack.
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