It shall be the duty of every employer of any person performing construction, maintenance or repair work inside any underground sewer which has been used as such to have safety information and equipment available at the work site. Such information and equipment shall include at a minimum (i) material for use as lifelines, (ii) equipment for venting of locations in the underground sewers where work is to be performed, (iii) individual oxygen masks or similar gear for each employee who works underground, (iv) chemicals or equipment to test for dangerous gas, and (v) equipment for prompt communications with emergency medical services.