NIOSH investigations of two confined space incidents with similar circumstances were reported. In Kentucky, two workers and two persons attempting rescue were overcome by gas or drowned when a check valve inspection plate they were attempting to remove blew off and caused raw wastewater to flood a 50 foot deep underground pumping station. Another rescuer became wedged in the access shaft and was removed and revived after 30 minutes. In New Mexico, a supervisor and an operator at a wastewater treatment facility were drowned when they attempted to repair a leaking pump without closing the valves to a primary digester, causing raw wastewater to flood the room. The inspection plate had popped up and discharged some sewage during removal, but the workers continued the operation. An extremely strong spray of wastewater began filling the room when all but three of the eight plate bolts had been removed. In this case, the operator died attempting to rescue the supervisor. The workers in both cases had no way of knowing if the pressure had been isolated to prevent raw wastewater and toxic gases from being released into the work area. NIOSH recommended that maintenance procedures which stress specific safety measures should be developed and implemented. A pressure sensing device or some other method should be used to determine if a line is under pressure when valves are closed. Specific safety questions that should be addressed prior to entry into a confined space were listed, covering the necessity for entry, issuance of a permit, testing of air quality, proper isolation of the space from other systems, proper training in protective and emergency equipment and for confined space entry, availability of ventilation equipment, and testing of air quality when the ventilation system is operating.