The safety discussion is nonsense. No use irl so no statistics. And any power storing feature will have dangers. It's energy. Dense. The denser the more dangerous. But not more dangerous than showering or crossing the street.
I hope the people building these things don't think that way... I'd like to keep showering the most dangerous activity in my day.
Mostly though, it's a new technology and interesting to think about. There's also a pretty broad variety of people with different areas of expertise on MR, so when things get technical it's not a bad place to learn.
Yes, different technologies have different dangers. What are they? It's not quite as simple as energy density... Sugar has a pretty high energy density relative to LiIon, for example, but the post office lets you mail it without special precaution. In part it's about the rate at which that energy is released which involves how volatile the materials are, physical barriers, and side reactions that occur in catastrophic events.
When a LiIon cell goes into thermal runaway (explodes), for example, the cause of the danger isn't the LiIon reaction which involves trading
LiCoO2 and LiC6, (or Mn, or whatever the cathode material is)-- that's just the match that starts the bigger reaction. The danger is that the heat of the cell starts making some nasty and highly
flammable byproducts in side reactions which aren't included in the energy density calculations for the battery. Chief among them, interestingly, is Hydrogen. The others are various flammable hydrocarbons, and then some carbon gasses. Heat plus hydrogen makes more heat and more hydrogen and it's off to the races. Fortunately the hydrogen isn't all generated at once-- it gets generated as more heat is generated.
Sugar, despite its energy density, isn't all that dangerous because it's solid at room temp so doesn't feed itself to the flame very readily.
Wood and plant matter aren't terribly dangerous in everyday life for the same reason, but get enough dust in a silo and give it a spark-- boom!
With hydrogen as a fuel, we've gone straight to the heart of the matter. If it's the hydrogen that makes LiIon and Lead Acid cells explode, then we've extracted just the exciting bit. But what affects hydrogen safety? There's two forms of hydrogen storage being discussed in this thread for example. One is highly pressurized gas, the other is captured in a metal hydride. Which is the better method?
Captured makes it sound less volatile, and exposes less actual gas, but heat releases the gas so is it at risk of thermal runaway similar to LiIon? Is a long burn better or worse than a quick one?
Pressurized gas on the other hand may make it harder to reach the right H to O ratio to burn with full efficiency. On the other hand, a breach will blow the full volume of gas out into the room quickly. 10,000 psi is just under 700 atmospheres. Air is about 20% oxygen, so the ideal ignition ratio would be about 40% hydrogen. So breaching a 10 gallon tank of hydrogen will very quickly fill about 70 cubic meters with gas at the ideal combustion ratio.
Toyota says they have an electronic cut off if the hydrogen leaks for example-- does that mean the whole vehicle has to be made intrinsically safe like mining equipment?
I don't know what all the risks are, but some of it is worth thinking about-- or at least fun to think about.
