Abstract: During maintenance work on the #19 tandem mill, millwrights, who had disconnected four hydraulic lines, forgot to reconnect them before energizing the hydraulic pumps. Consequently, when the pumps started, hydraulic fluid was sprayed into the atmosphere at the north end of the mill. The atomized hydraulic fluid then came in contact with an electric space heater that was in service approximately 17 feet from the nearest hydraulic line. A flash fire completely engulfed the mill and injured Employees #1, #2, #4, #6, #8, #9, #10, and #12 through #17. Only Employees #2, #4, #6, and #9 were hospitalized.