Two workers were repairing a process vessel at a pulp mill. The valves to the
vessel were locked out, but a nitrogen supply to the power boiler was not
locked out because it had not been identified in the lockout procedures.
Nitrogen gas inadvertently leaked from the boiler system into lines that
fed into the process vessel, displacing the oxygen and creating an
IDLH (immediately dangerous to life or health) atmosphere.
The vessel was a confined space. Appropriate confined
space entry procedures to the vessel had been followed
on previous entries. However, on this re-entry, the
atmosphere was not tested and the space was not
ventilated. One worker entered the vessel and
collapsed from oxygen deficiency. The second
worker, who had been watching outside the
entrance hole, was found collapsed with his
head inside the vessel.
Safe work practices:
- Consider each entry to a confined space to be potentially deadly. Proper testing and
safe entry procedures must be followed for each entry.
- Identify and label confined spaces in the workplace.
- Provide written safe work procedures for entering a confined space and ensure that
workers are trained in these procedures.
- Isolate the confined space from adjacent piping by blanking, blinding, or disconnecting
the piping.
- Assess the hazards before entering a confined space,
including testing for oxygen levels if necessary.
Note: This hazard alert is based on an accident that occurred in 1997.
