Abstract: At approximately 8:30 a.m. on March 31, 1994, a strong noncondensible gas main line to the #12 boiler experienced a pressure buildup when the main gas line water loop seal drained into an open sewer. Employee #3 was in the vicinity of the drain and observed that his hydrogen sulfide monitor's alarm had been triggered. He asked Employee #2 to come over to verify his hydrogen sulfide monitor's reading. Employee #2 went to the control room to get pencil and paper to log the readings and on his return to the leak location told Employee #1, his supervisor, that the monitor's alarm had been triggered. Employee #1 left the control room to follow up by checking on water loop seals on the deck above. Noticing an odor and observing Employees #2 and #3 by the drain, he told them to leave. He attempted to fill the water loop seal twice and went into the gas leak area twice to see if he could see water flowing into the sewer from the loop seal drains. He left the area and called the kiln operator to shut off the gas to the boiler but could not reach him by radio. Employees #1, #2, and #3 reported to the medical center suffering inhalation symptoms. Employee #4 went to a doctor at about the same time with similar inhalation symptoms. Two employees were sent to the hospital and treated with oxygen before being released.