A case study of two confined space fatalities in a natural gas field fracturing tank was investigated. The crew consisted of two service rig hands and their supervisor, a service rig operator, rig supervisors and a service rig tool pusher. The crew was required to blow down the gas well to relieve the internal pressure. After the well had blown down sufficiently to begin inserting the flow back tubing, the operator and one of the rig hands began to disconnect the well from the fracturing tanks. Gas, water, acid, and oil were directed into the fracturing tanks through 2 inch steel flow back lines. The remaining members of the crew were near the service rig, assembling the down hole equipment when they heard that the rig hand was in the tank. The operator, tool pusher, and other rig hand entered the tank to rescue the first rig hand. A rescue squad was notified by the supervisor and arrived at the scene. The bodies of the operator and tool pusher were found lying on the bottom of the tank. One of the rig hands was found standing in the tank and was unresponsive; the other rig hand, also unresponsive, was found attempting to climb up the internal support bars of the tank. The two rig hands who had entered the tank and survived the incident reported that within 10 to 15 seconds of entering, they were overcome by the gas. The autopsy reports indicated that the rig operator and the tool pusher died by drowning from asphyxiation. The authors recommend that a confined space policy and appropriate procedures be established by the company, that a training program be developed, and that a procedure that makes metal flow back lines be made mandatory.
Division of Safety Research, NIOSH, U.S. Department of Health and Human Services, Morgantown, West Virginia, Report No. FACE-85-2, 5 pages