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Two employees die after steam line they were repairing was re-energized.

NIOSH 1996 May; :1-7
Two employees of a commercial steam heat supplier died of injuries they sustained when a steam line they were repairing was re-energized. The day before the incident, the two victims and a coworker went to an underground vault to investigate a steam leak. They suspected that the leak was from a flange in a steam line that served as an interconnect line between two steam generation facilities. The next morning, they told the facility 1 operator that they were going to facility 2 to shut down the leaking steam line before repairing it. At facility 2 they closed two control valves to isolate the leak in vault A. They did not lockout and tagout either of the control valves. After closing the valves, they drove to the site of the leak and began to mechanically ventilate the vault. While the vault was being ventilated, they went to vault B and closed a second isolation valve. They returned to the site of the leak (vault A) and entered the vault after the steam was cleared from it. They confirmed that the leak was due to a defective flange gasket and disassembled the steam line flange. The repair task was slowed for several hours since the workers initially did not have the correct size wrenches for the flange bolts. They were also delayed when the disassembled line became misaligned as it cooled. Because of the delays and the need for alignment pins to reassemble the line, the workers stopped for lunch and returned in the afternoon to finish the repair. When the workers returned, the two victims entered vault A while the coworker remained above ground near the entry to the vault. While the two victims realigned the steam line flanges, the facility 2 operator started a boiler in preparation for a boiler test. He contacted the facility one operator to determine the status of the steam line repair work. He apparently understood that the repair work had been finished and that the interconnect line could safely be re-energized to provide additional steam for the boiler test. A facility 2 maintenance engineer opened both control valves and released steam into the interconnect line and the vault where the two victims were working. Both victims were able to escape from the vault within seconds after the steam entered the vault. The coworker who had been outside the vault, called facility 1 by radio and requested immediate emergency medical assistance. Both victims were transported to a local hospital where one of them died approximately one week later and the other died three weeks later. MN FACE investigators concluded that to reduce the likelihood of similar occurrences, the following guidelines should be followed: 1. employers should develop, implement and enforce a written safety program which includes task-specific training and lockout/tagout procedures; and 2. employers should ensure that when more than one employee is exposed to hazardous energy, a procedure is in place for group lockout/tagout.
Region-5; Accident-analysis; Accident-prevention; Accidents; Injuries; Injury-prevention; Traumatic-injuries; Work-operations; Work-analysis; Work-areas; Work-performance; Work-practices; Safety-education; Safety-equipment; Safety-measures; Safety-monitoring; Protective-measures; Steam-boilers; Steam-generators; Safety-programs
Publication Date
Document Type
Field Studies; Fatality Assessment and Control Evaluation
Funding Type
Cooperative Agreement
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
FACE-96MN001; Cooperative-Agreement-Number-U60-CCU-507283
SIC Code
Source Name
National Institute for Occupational Safety and Health
Performing Organization
Minnesota Department of Health