Section 3309 - Drainage and Ventilation(a) Trenches, tunnels and pits inside buildings shall have proper drainage and ventilation, or other means of protecting employees who work in these areas shall be provided as required in Group 16 of these orders.(b) Sewage tanks and sewage sumps inside buildings shall be tightly covered and ventilated with a suitable vent to the outside atmosphere so located as not to endanger the safety of employees.Cal. Code Regs. Tit. 8, § 3309