OSHA does not set a max number of cylinders to be chained. There are far too many veriables to simply assign a number. If you have a 3 walled storage area that can hold 12 cylinders but is 12 deep by 1 wide, how would the chain be inadequate? If you have 12 cylinders against a wall with one chain, then I would say it needs addressed. This is one of those areas where OSHA wants you to have good judgement, and if you don't you could be cited for General Duty Clause violations.