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Comment by btilly | Hacker News Reader

Wait, what? We're putting laptops in luggage because we're afraid that they are bombs. But laptops stored closely together in luggage with pressure changes can explode..and we don't know how to handle that.

In the name of safety we're introducing a restriction that makes people and airplanes less safe!

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What part of the previous 16 years caused this to be a surprise to you?

I'm not surprised.

Laughing cynically, however...

Luggage storage in modern jets is pressurized. No more pressure changes there than in the cabin. The pressure vessel is a tube, not a half-tube.

Good point. However if a fire got started (and batteries sometimes do that), it could get going well before anyone noticed.

Anyways the concern about the batteries in the hold is straight from the article.

Well if you think about it, it makes sense. Something could be potentially improvised by a passenger. But to make a device, you would open yourself to detection via X-Rays. However, I think that the rest of the world should return the favor and ban all laptops from US incoming flights. Just as a quid pro quo.

Soon though hopefully solid state cells will come into play and this will no longer be a problem. China for instance has banned shipping all lithium ion batteries via China Post and searches actively for them... as it's a risk. You have to ship them specially declared which is pretty expensive.

> I think that the rest of the world should return the favor and ban all laptops from US incoming flights.

I mean, that will basically be the case anyway. If I leave the US, I'm not taking a laptop since I can't bring it back.

The rest of the world should ban american citizens from carrying laptops on US incoming flights.

Oh, and also charge them the equivalency of the ESTA fee.

and submit them to TSA-style questioning on landing.

That would just be inhumane.

>China for instance has banned shipping all lithium ion batteries via China Post

Fedex and UPS both treat lithium ion batteries as dangerous goods, with the exception of batteries shipped "with equipment" i.e. shipping a laptop with its battery, without the battery being plugged in.

How does that make sense? If item A is dangerous, how does putting item B in the same shipment suddenly make item A not dangerous? Is the non-powered-on laptop capable of putting out fires or something?

The Chinese rule is extremely annoying, but I'm forced to admit that at least it makes logical sense.

[0] https://www.ups.com/content/ca/en/resources/ship/packaging/g...

[1] http://www.labelmaster.com/fedex-battery-shipping-policy

The likelihood of shorting exposed terminals on a lithium ion battery is lower if those terminals are enclosed in a device.

The likelihood of crushing a lithium ion battery is lower if the battery is enclosed in a device.

"With equipment" doesn't require the battery to be actually plugged into the laptop. Most laptop manufacturers ship the laptop and the battery in separate plastic bags, and this still qualifies for the exemption.

The rule would make a lot of sense if it requires the battery to be plugged in, but it doesn't.

This is true. You can read about safety incidents involving Li batteries carried as cargo on airplanes. It's surprising what people will do - like put a spare Li battery in a plastic bag with a bunch of cables and wires. A wire then falls across the terminals, and you have trouble.

Less chance of the battery terminals coming into contact with a random conductor and short circuiting, maybe?

totally unrelated, but I'm doubtful that pressure changes have any impact whatsoever on li-ion batteries. The materials in a battery expand by 13.4% between discharged and charged, and the PTC (safety disconnect) goes off at 145 psi. The can itself takes thousands of psi before it blows. The minor pressure difference at altitude shouldn't be able to distort the can enough to mess with the materials inside.

This doesn't hold for things like pouch cells, which can and have been affected by altitude changes (leading to problems in airplane batteries). Standardized cylindrical cells like those in a laptop should be fine.

You don't have any control over where your luggage gets placed in the hold. In the cabin, however, you can ensure a bomb explodes, say, on a window.

Checked bags go through a CT scanner, carry on just goes through an Xray scanner. The CT scans are much more detailed, so the thought is that potential explosive devices are easier to detect in checked bags than ones carried on. At least, that's the reasoning I've heard.

On long-haul flights, checked luggage is placed in containers that are built to withstand bombs.

No, they're not. That would be far too heavy. The containers are regular aluminum lined unit load devices (https://en.wikipedia.org/wiki/Unit_load_device). They are not resistant to explosives.

Some airlines that are particularly sensitive (El Al, for example) have additional mitigations like a reinforced floor between the cargo and passenger compartments or one particular piece of the cargo hold that's more structurally sound for sensitive items, but wide body aircraft do not have "containers that are built to withstand bombs". It's just not practical to do so.

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