alt Hacker NewsLimiting the devices to two per person seems nonsensical to me. The devices are either dangerous, or they're not. If they're dangerous, two is too many. And if they're not, then why limit them only to two?
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Maybe it's a sort of build-quality proxy.
Someone bringing 150 "lipstick" single-cell promotional chargers -> bad
Someone bringing one phone and one laptop battery pack -> OK
If you are limited to two, you are probably not bringing anything that is near e-waste quality.
If one power bank has independent probability p of failure, then n of them have probability 1 - (1 - p)^n of failure.
What you're saying is equivalent to claiming that this quantity is somehow independent of n.
These items are dangerous. The FAA limit for power bank capacity is 100Wh (~27000mAh), which is 360kJ of energy. A hand grenade has approximately 700-800 kJ of energy.
Two powerbanks contain the same amount of energy as a hand grenade.
More batteries, more likely that you'll have even just one of them fail. Since even one of them (to your point) failing is enough of a reason to divert the flight, better to start by reducing the probability of that happening in ways people can swallow.
Quantity is a quality of its own.
Maybe there is enough plane onboard capacity to deal with just 50 batteries, let's say; multiply the failure rate expected and the pax capacity of the plane and you get how many batteries you can afford to have onboard and still be able to deal with worst case scenario.
> The devices are either dangerous, or they're not
That's not actually how it works though, it's all a risk and percentages. Nobody says "driving is either safe or it's not" or "delivering a baby is either safe or it's not"