I also had a Lipo fire about 18 months ago after charging (approximately two hours earlier). I had two new 4 cell 2850mAh packs that I'd used for one flight each in an EDF that morning. Both packs were discharged to approx 30% after flying. Charged them up in the evening on my Hyperion charger and both took about the same amount of charge (I track the mAh put back into the packs when I charge). I keep my Lipo's in an ammo box but I was lazy this time and had left both charged packs sitting on the lower shelf of my timber workbech, sitting on an old newspaper next to my flight box with nitro fuel in its container. I know, I know...
I couldn't sleep after going to bed when the packs had finished charging so I went back into the garage to potter about. Whilst working on a model on the bench above the batteries I heard a pop/fizz type sound and looked down to see one of the packs start bellowing thick smoke. It filled my double car garage in about 30 seconds whilst I grabbed the fire extinguisher off the wall. As i kicked the battery off the shelf it caught fire and went ballistic skidding across the concrete floor.
I still use the other pack that I bought at the same time as the pack that went up after being used once and its had many cycles. The pack that caught fire had no impact damage from my use and no sign of shipping damage from purchase, must have just been some sort of internal fault.
I'm just glad I went back into the garage that night as its at the other end of the house from our bedroom with the kids bedrooms in between. There are smoke alarms but...by the time we would have heard them the whole garage would have been ablaze by then.
I still use Lipo's and store them all together in a 'stored' state in that ammo box but I dont keep that box of batteries under my roof line anymore and I don't charge my batteries on or near anything combustible.
Hope this helps someone, Lipo fires are nasty things.