26.C.03 Ventilation.
- Fresh air must be supplied to all underground work areas in sufficient quantities to prevent dangerous accumulation of dusts, fumes, mists, gases, or vapors.
- Mechanical ventilation must be provided in all underground work areas except where it is demonstrated that natural ventilation provides the necessary air quality through sufficient air volume and airflow.
- (1) Ventilation and exhaust systems for tunnel excavation must be of sufficient capacity to maintain an adequate supply of uncontaminated air at all points in the tunnel.
- (2) The supply of fresh air must not be less than 200 CFM (94.4 L/s) each employee underground plus that necessary to operate the equipment.
- (3) The linear velocity of air flow in all underground work areas must be at least 30 ft/min (0.15 m/s) where blasting or rock drilling is conducted or where there are other conditions likely to produce dusts, fumes, vapors, or gases in harmful quantities.
- (4) The direction of mechanical airflow must be reversible.
- (5) Ventilation doors must be designed and installed so that they remain closed when in use, regardless of the direction of airflow.
- Following blasting, ventilation systems must exhaust smoke and fumes to the outside atmosphere before work is resumed in affected areas.
- Potentially gassy or gassy operations must have ventilation systems installed which are constructed of fire-resistant materials and have acceptable electrical systems, including fan motors.
- Gassy operations must be conducted with controls for reversing the airflow of ventilation systems located above ground.
- In potentially gassy or gassy operations, wherever mine-type ventilation systems using an offset main fan installed on the surface are used, they must be equipped with explosion-doors or a weak-wall having an area at least equivalent to the cross sectional area of the airway.
- Air that has passed through underground oil or fuel-storage areas must not be used to ventilate work areas.
26.C.04 When drilling rock or concrete, appropriate dust control measures must be taken to maintain dust levels within safe limits.
26.C.05 Internal combustion engines, except diesel-powered engines on mobile equipment, are prohibited underground.
26.C.06 Mobile diesel-powered equipment used underground in atmospheres other than gassy operations must be either approved by MSHA (30 CFR 36), or must be demonstrated to be fully equivalent to such MSHA-approved equipment, and must be operated in accordance 30 CFR 36.
Knowledge Check Choose the best answer for the question.
26-8. The linear velocity of air flow in all underground work areas where blasting or rock drilling is conducted or where there are other conditions likely to produce dusts, fumes, vapors, or gases in harmful quantities must be _____.
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