Don't expect the case to give you time to throw the battery outside, either. Lipo don't burn that way.
I made this video mostly for fun, but it's also an experiment in how Lipo burn so I could build a safer bike. That's a thick cast iron pot. If you watch carefully in the half second before the cell explodes, it vents. the vented gas circles around the cast iron pot, and then when the cell ignites a half second later, it causes the vented gas to explode in what I think is called a thermobaric explosion.
Had I not partially trapped the gas, it would have just burned fiercely like a road flare, but not exploded.
This experiment lead me to 2 conclusions.
1. I needed to contain the cells in an oxygen free container so they couldn't get air. Unfortunately, the cells vent before they burn, and I have no idea how much pressure they can exert. Trying to contain an explosion actually makes the explosion more powerful, so if I got it wrong, my efforts would just make it worse.
2. OR i could get rid of the vented gas as quickly as possible. The video shows the vented gas stays in the pot, instead of rising up, and other videos of lipos venting shows they vent the gas a good distance away, but the gas can become trapped.
So my solution was to build a tight fitting case that protects the cells, but will blow apart if any cell starts to swell, long before any cell vents. That case is built into my bike frame. If a cell starts to swell, the sides, top, and bottom of the battery case will pop off their panels, and expose the battery to as much fresh air as possible. It won't stop the fire, but it will hopefully prevent the explosion.
Keep in mind this is just 1 cell going up. You may have 20-40 cells this size depending on what size battery you go with.
[youtube]NzUla1udKuA[/youtube]