This post is relevant!

https://forum.allaboutcircuits.com/threads/lithium-ion-battery-incident.169005/

 

I saw a radio controlled model airplane Li-PO battery catch on fire. Its battery was new and this was the first time it was used. Water and sand did not extinguish the fire. I think the plastic case on a Li-PO battery swells then pops, without exploding like a metal cased battery.