Li-ion Swollen battery dangerous or not?
Provided it hasn't been over-charged, over-discharged or physically damaged it should be safe. But, why did it puff up? If it was overcharged, over-discharged or physically damaged then it could blow up. 

Apart from that, puffing indicates that some of the electrolyte has turned into gas, which reduces the capacity and efficiency of the cell.

You should discharge this cell to zero volts, discard it and get a replacement.