Earlier quoted context omitted.
Kind of dangerous seems like quite the understatement, considering the nature of lithium batteries! It'd be fun to play with something like this for the learning, but I wouldn't actually run one unless it was in its own shed, many dozens of yards from the nearest anything else. Lithium fires are no joke.
BTW I've seen lithium cell safety bags, that can hold the flame enough. I wonder how a case could be done in a similar way to at least contain the heat and gas. Also, could there be a thermoelectric powered fan to slow down the heat rise when cell(s) starts to fail or burn ?
You absolutely can design a firewall system able to fully contain a runaway pack. They have small systems that look like briefcases to nab runaway laptops on planes, for example. But when a cells goes, it goes. No fan is going to remove anywhere near enough heat. And you wouldn't want it to spread the vapors, as HF is a genuinely dangerous byproduct. The only real solution is full containment. And being 100% confident in your containment solution would require a lot of destructive testing- it isn't a trivial problem.