Cal. Code Regs. tit. 8, § 7093 – (5-3). Dust--Rock Drilling.

(a) For the purpose of these Orders “rock drilling” means drilling, cutting, chipping, channeling, or broaching rock by means of machinery.
“Wet drilling” means the continuous application of water through the central hole of hollow drill steel to the bottom of the drill hole.
(b) Rock drilling in underground mines is prohibited unless the dust is controlled by wet drilling or other means acceptable to the Division.
(c) Rock drilling machines purchased and used for wet drilling after the effective date of these Orders shall be equipped with a combination air throttle and water valve, so designed that the air cannot be turned on without turning on the water, and the water cannot be turned off without turning off the air.
(d) During wet drilling, the water flow shall be maintained continuously whenever the drill is in operation, including the period of collaring or starting the hole.
(e) Water for wet drilling shall be supplied to the drill in adequate quantities at a pressure of at least 40 pounds per square inch.
(f) Should the water supply or pressure for wet drilling become inadequate, such drilling shall be stopped immediately.