Cal. Health & Safety Code § 108605

On or after January 1, 1984, a visually inspectable without disassembly, pressure-relief rupture apparatus or other pressure relief device that performs equivalently shall be required on beer dispensing equipment manufactured, rented, leased, sold, or distributed that uses an external source of pressure, other than hand pumping. This apparatus is not required to be placed directly on the keg itself. On or after January 1, 1984, a warning shall be clearly displayed on or securely attached to all beer kegs. The word “WARNING”, “ATTENTION”, or other suitable wording shall appear in capital letters. The remainder of the warning shall read substantially as follows: “This keg will rupture and may cause injury if overpressured with compressed air or CO 2. Tapping system and pressure regulator should be equipped with a pressure-relief (blowoff) device. If you are not familiar with tapping equipment, consult your retailer or the local beer distributor.”