When Seagal kills one of the convicts in an orange jumpsuit, he can be seen falling on the ground with his shank falling beside his torso under his left arm. In a later shot, the shank is laying by his right hand.
After Manning kills the henchman with the chain, you can see him move.
A BBQ propane tank holds barely 200 PSI and will not shoot across the room like a 3000 PSI SCUBA tank.