Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.
It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.
I've personally set RC lipo on fire with the wood-nail-hammer technique and while the fire out of the pack is intense I can't imagine it igniting another pack.
If we could develop some basic standards for packs (which voltage steps per row and some kind of connector interface standard like for charging) I think we have a really good way to maximize the lifetime and use of EV batteries to help the environment.
I paraphrase Bill Gates: There's no one energy source which will save us, many will complement eachother.
If one battery pack catches fire, you can start moving the others away from it.
If you normally keep 0.5m between them, you have plenty of buffer space to eat into.
Basically it would start as . . . X . . . with X being the pack on fire "." being a battery pack not on fire, and " " being the half metre between them. Then you move them to get:
... X ...
Where the dots now have perhaps only 30cm between them, but the space to the X is increased.
Your interpretation seems to be "we don't use caution when building them" which is not what I meant at all, we do but the risk is non-zero.
Yes. Dams in particular. You calculate for various failure modes and you design around mitigating the disaster if failure should occur. That's why dams are designed with emergency spillways. If there is a bunch of rain, gate failures, etc and you suddenly have more water than you know what to do with, you have the emergency spillway as a last resort. They exist to route water in high volume out of the resevoir, often in a sacrificial manner in an attempt to prevent the dam from failing. And if a dam would fail, it's preferably that it do so at the emergency spillway than elsewhere. So there is a certain amount of "in certain conditions failure can/will happen so this is how we design the system to fail as gracefully/least destructively as possible".
Nuclear has this as well. The plans for this are called "Severe Accident Mitigation Guidelines" or SAMGs with the general practice being called SAM (same abbreviation, just drop the G). Each nuclear site has them and they are generally framed as "this shouldn't go wrong but if it does". You can try to avoid those failure modes but they can always still potentially occur and the most you can do is just try to keep the damage from spreading to the best of your ability.