Swollen battery: my questions

I purchased an iPhone 3Gs off of ebay in a lot. I charged it a little, but not so much.

Yesterday, I disassembled it and noticed that the logic board was bent because of a swollen battery. I decided to tear down the logic board. The battery was effectively quite swollen. I’m almost sure that the battery is original from Apple.

Today, I noticed that the battery continued to grow, because since I put off the logic board, it has more room to grow. Should I worry? I’m keeping the battery, still glued to its housing on my wooden shelf. I know that I shouldn’t keep it there, but I really don’t know where else I could put it. I must look for a metal box to put the battery inside with some sand.

So, please tell me, now that the battery has almost no chance to be punctured, can it still continue to swell or worse, catch in fire?

(A few weeks ago, I had an iPhone 5s swollen battery and it finished by un-swelling by itself)