Mines create special problems in proper ventilation by their isolation from fresh air sources, and the presence of dangerous gases and dusts. Large fans are used for the stationary systems, while small portable types provide fresh air in dead-ends and other 1997 inaccessible locations. These fans may be driven by electricity or compressed air, and in addition to mine operations, are useful for work in manholes, pipe galleries, silos, tanks, vats, plane fuselages, ship holds, etc. The Mine Safety and Health Administration, Department of Labor can furnish specific recommendations concerning special problems.