Cal. Code Regs. tit. 8, § 7110 – Shaft Guarding.

(a) (19-100) Every shaft shall be guarded at the top and at every shaft station.
(b) Guards for shafts shall conform to the following standards;
1. (1) The guards shall be substantially constructed, preferably, of solid materials, to keep objects from falling into the shaft. If solid materials are not used, openings in the guard shall not exceed one-half inch.
2. (2) The guards shall be securely fastened in place and, except when necessarily opened, the gates shall be kept securely closed.
3. (3) The guards and gates shall be at least 42 inches high and shall fit as closely to the floor as feasible.
4. (4) Any alternate means of guarding which will afford at least equal protection to employees and is acceptable to the division.
(c) The guards for all shafts shall be kept closed except when necessarily opened to:
1. (1) Load or unload the shaft conveyance.
2. (2) Make repairs to shaft.
3. (3) Perform other operations that cannot be performed with the guard in place.
  At all times when a guard is removed, the employer shall provide other effective means to prevent men or materials from falling into the shaft.
(d) When a bucket or skip is used for hoisting, means shall be provided that will prevent material from falling into the shaft while being dumped.
(e) (19-105) All stations, levels, and skip pockets shall have a passageway around the working shaft where it is necessary for employees to cross through the shaft.
(f) Entering or crossing through a shaft, except to ascend or descend or for the purpose of inspecting or effecting repairs, is prohibited.
(g) In inclined shafts where the dip exceeds 45 degrees from the horizontal and men are hoisted in skips, the space between the hoisting compartments at each level station shall be closed by lining boards; and an iron bar or pipe of approximately 1-inch diameter shall be placed overhead above the divider in order to give men an easy and secure overhead handhold while walking on the divider.
(h) (19-101) Positive stopblocks or a detail switch shall be installed on all tracks leading to a shaft collar or lading.