Are your batteries ready to fly?

-August 08, 2014

We are so used to the ubiquitous availability and use of rechargeable batteries – now, mostly lithium-based – that we also can get complacent about their dangers. Sure, most engineers developing products have heard about the smoldering, smoke, and even fires associated with these lightweight, high-density electrochemical energy-storage units, but haven't had to worry about the implications. After all, only a small fraction of designers are doing work on projects such as the Boeing 787 Dreamliner battery system.

Nonetheless, many designers use battery packs with integral charging and over-temperature monitoring and protection, either because they are required by regulatory and safety mandates, or because it makes good sense and is relatively inexpensive. However, the dangers of Li-based cells in both charged and uncharged states may soon affect all designers and the design requirements they must meet.

A recent article "In-Flight Battery Fires Stir Safety Questions" in The Wall Street Journal (sorry, it may be behind their paywall) reported that "the U.S. Department of Transportation issued new standards for air-cargo shipments of various types of lithium batteries, including packaging requirements and safeguards for power cells that have been damaged or are headed for recycling." The article also noted that is is already forbidden to ship lithium batteries in the cargo holds of US passenger jets, but non-US airlines do not have this restriction, at least not yet.

The International Civil Aviation Organization (ICAO) is looking at comparable regulations. Right now, there are no restrictions on the batteries that passengers bring on board with their personal devices, and it doesn't seem like any such restrictions are planned soon. Obviously, the practicalities of such moves would be enormous.

The FAA lists 17 battery-related "incidents" over the past decade, including some smoldering personal devices in overhead compartments. Depending on your perspective, the risk from these "personal" batteries is either a big potential issue, or a small one. Compared to the number of flights, passengers, and devices carried over that time period, that's a very, very small number, and a smoldering battery in a passenger cabin is not as stealthy a risk as batteries in a cargo hold (hmmm ... what about such batteries in the passenger checked-luggage compartment?).

No doubt, any fire or even potential fire on an aircraft is a big deal. The question is: at what level of battery capacity do you start to really worry? How many A-Hr of full charge constitutes too much risk? The article points out that the big danger is in shipping these batteries in bulk from their factory to the OEMs who are inserting them into products and major shippers have programs to manage the risk; but that doesn't address individuals and their personal devices.

According the article, Google's own jets carry on-board an interesting product called Planegard (HighWater Innovations LLC), which is designed to contain the intense fire of a lithium battery. Just spraying water on such a fire is not advisable, and halon-based extinguishers are also not the answer. The Planegard approach is a sealed double-walled containment case into which you put the smoldering device, and then pump in water between the walls. (Check out their web site and videos for more a more vivid description.)

We've all been told that "better batteries" are key to longer run times, more practical electrical vehicles (EVs), and enhanced storage for solar and other "green" renewable sources. But a better battery will also be a denser package of concentrated energy – just like gasoline and other hydrocarbons. After all, you can't just casually carry a can of gasoline around with you, and these improved batteries – if and when they come – may force a change in thinking as well as some very careful design, testing, safety features (packaging and electronic) and more, depending what they are made of and how they are constructed.

As with so many advances, they always have to be looked at along with two admonitions: "be careful what you wish for, you might get it" and "beware the law of unintended consequences." How the battery-risk story evolves is almost anyone's guess; I'm too humble to make predictions.

Have you had first-experience with these sorts of battery issues? What concerns do you see from your design standpoint as we pack more energy into smaller devices, or put large arrays of batteries in fixed installations?

Dreamlining Boeing and batteries
The Dreamliner saga: when your solution is more than just a software patch

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