Abstract: Some employees were drilling a 160-millimeter-diameter access hole to an underground salt formation used as a storage container for liquid propane and butane. The top of the storage container was 902 meters below the surface. At a depth of approximately 872 meters, the drill string apparently encountered a pocket of liquid propane, which escaped to the surface before the blow-off preventer could be activated. The propane evaporated, and an ignition source ignited the vapor. The resulting explosion and fire burned three employees of Gas Field Specialists, Inc., and one employee of Inergy Midstream, LLC. Three of the burned employees were hospitalized, and one was treated and released.