To have the underground working places in the mine examined for hazards by competent personnel designated by the operator to do so, at least once during each coal-producing shift, or oftener if necessary for safety. Examinations shall include tests with a multi-gas detector for methane and oxygen deficiency. In all underground face workings where electrically driven equipment is operated, examinations for methane shall be made with a multi-gas detector by a person trained in the use of such multi-gas detector before equipment is taken into or operated in face regions, and frequent examinations for methane shall be made during such operations.