Section 6990 - (3-20). Timbering-General(a) Every working place in the mine shall when necessary be kept securely timbered or otherwise supported to prevent injury to employees from falling material.(b) All miners shall be supplied at all times with the timbers or other adequate materials which are necessary to keep their working places in a safe condition.(c) If for any cause necessary timbers are not available, work at that place shall cease until timbers are supplied.(d) It is recommended that wood preservatives be used to increase the useful life of mine timbers. Such preservatives should be of a type which will not irritate the skin or increase the flammability of the timbers.Cal. Code Regs. Tit. 8, § 6990