If you have the space for it, just put it outdoors 5' from anything flammable and you're good to go. This is not a hobby for folks in apartments unfortunately.
I've had one of my DIY ebike batteries short and fail spectacularly at near full charge and was able to push it with a broom out of the garage into the driveway before any damage was done. Now I have a bench with wheels that I can take into the driveway for initial testing.
At least not neighbors likely to be alarmed when their neighbors run out of their garage at odd hours of the night, pushing a flaming cart and screaming "fire!"...
I've had one of my DIY ebike batteries short and fail spectacularly at near full charge and was able to push it with a broom out of the garage into the driveway before any damage was done. Now I have a bench with wheels that I can take into the driveway for initial testing.