Aviation fire-safety consultant John Cox

John Cox is a retired US Airways airline captain who runs an aviation safety consulting company, Safety Operating Systems, and specializes in in-flight fire issues. As the Department of Homeland Security (DHS) debates expanding its ban on large electronic devices in carry-ons to include flights from Europe to the U.S., Cox spoke with news editor Johanna Jainchill about why it is risky to store devices like laptops that use lithium batteries in the cargo holds of commercial aircraft.

Q: What's the risk of having laptops in cargo holds instead of passengers' possession?

John Cox
John Cox

A: A given number of lithium batteries are going to spontaneously combust. Last year, the FAA had 32 reports of lithium batteries that went into a phenomenon called thermal runaway (TR). Once TR begins, unless you can cool the battery, it will continue until it exhausts all of the cells contained in the battery pack. That almost always means an open fire with very toxic, highly flammable fumes. Lithium batteries have a known failure rate, and anytime they are subjected to heat that failure rate goes up dramatically. That's the issue. If they are in the cargo hold and one of these batteries goes into TR, it will cause batteries in proximity to also go into TR, and you can have quite a significant fire that the extinguishers in the airplane can't put out. In the cabin, the crews for the most part are trained to cool the device down, and that stops the TR.

Q: Why can't the extinguishers put them out?

A: The extinguishing systems in cargo holds use halon 1211, a compound that will knock down the open flame but will not stop the TR, so reignition can occur. Cargo compartments also work on the premise that a fire requires oxygen, and these compartments have a limited amount of oxygen. But unfortunately, a byproduct of TR is it makes its own oxygen in this enclosed environment. Another byproduct is hydrogen. When you have hydrogen in an enclosed space, it can become very explosive.

Q: So, flight attendants are trained to put out these fires?

A: When a device is in TR, it emits a lot of smoke, so you usually get some warning that it is about to happen. There is some conflicting guidance on how to deal with it, but, all in all, you're better off dealing with it early and effectively. If it's in the cargo hold, you can't deal with it at all.

Q: If the danger is so obvious, why aren't the airlines pushing back about these rules?

A: To my knowledge they are. The DHS doesn't appear to be listening to very many people because they are not really including the FAA in these conversations. They are just saying, 'We have a security concern,' and they are not willing to provide any risk analysis and go through the normal steps that aviation safety goes through when there is a potential to add risk into a flight. I've been asking since the beginning, 'Where's the risk analysis?' and no one will answer that question.

Q: As a pilot, would you feel safe flying an airplane with all of these batteries in the cargo hold?

A: I wouldn't be real happy about it. I think they've added as much risk as they have mitigated. If the risk is so great that [laptops] shouldn't be in the cabin then my question is, why is it OK for them to be in the cargo hold? There is an inconsistency here that is clouded under [the information being classified]. I don't need to know how they know this. All I am interested in is the risk and how we're going to mitigate it to an acceptable level. I'm an aviation safety guy, so that's the only thing I look at. And so far, they haven't been forthcoming at all. It's very frustrating. Lithium battery fires and drone strikes are about the only two rising risks in aviation; everything else is getting safer. Now you want to degrade the safety net around the lithium batteries. Philosophically, I have a problem with that.

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