Cal. Code Regs. tit. 8, § 3304 – Miscellaneous Use of Compressed Cylinder Gas.

(a) Employers shall not permit the use of compressed cylinder gas for testing pressure vessels unless there is installed in the compressed gas supply line or on the vessel being tested a pressure relief device set to function at a pressure not to exceed the safe working pressure of the vessel.
(b) Compressed gas shall never be used from a cylinder or cylinder manifold where pressures dangerous to employees may develop unless an accepted pressure regulating device is installed on the cylinder valve or manifold. The term “accepted” here means that the pressure regulating device is listed by Underwriters' Laboratories or some other recognized authority of equivalent standing.
Note: Cylinder as used in this order means an Interstate Commerce Commission compressed gas cylinder.