Two scientists were changing hydrogen gas cylinders in an analytical laboratory. They were in the process of removing the cylinder cap from the new cylinder when a loud hissing noise occurred and they quickly realized that the tank was leaking. After making a quick attempt to shut off the tank, which was not possible, they left the lab and notified their supervisor.
After checking that everyone was out of the lab, the supervisor paged all staff in the vicinity to immediately evacuate to the staging area. Facility management and ES&H management were notified about the situation, and they contacted the local fire department to respond to the site in case the venting gas was ignited.
The first responders arrived quickly and spoke with facility management and the site safety officer. Everyone agreed that the best course of action was to allow the tank to vent until it was empty. The hydrogen gas supplier was called, but a specialist was unavailable at that time. Based on information from the hydrogen supplier's website and some basic estimates of the hydrogen release rate, facility staff determined that the contents of the tank should have been completely vented. A decision was made that the first responders would approach the lab in full bunker gear with SCBA and a gas detector (Lower Explosion Limit (LEL) meter) to evaluate if there was any gas present. If they heard any hissing coming from the tank or if there was any reading above "0%" on the LEL meter, the team would immediately pull back and reassess the situation.
Two first responders entered the lab and two were stationed as back-up. Upon entry to the lab, the first responders indicated that they did not hear any hissing and proceeded towards the cylinder with the LEL meter. Their readings confirmed that the cylinder had vented and the lab was clear and safe to enter. The hydrogen cylinder was moved outside and secured and later returned to the supplier.
LESSONS LEARNED:
- Compressed gas cylinder caps can be very difficult to open as rust often occurs in the threads.
- There are wrenches specifically designed to remove compressed gas cylinder caps. The lab had such a wrench and it was the one used by staff at the time of the incident. (See attached photos.)
- The wrench designed for the cylinder caps is short and often does not provide enough leverage to easily open the cylinder caps. Staff indicated that they often reverse the wrench, pushing it through one of the cylinder cap openings to gain additional leverage on cylinder cap lids. They indicated this was a common practice with exceptionally difficult cylinder cap lids and they did not believe it could interfere with the cylinder valve.
- The training program did not prohibit using the valve cap wrench in the manner it was used.
- The cylinder was empty when it was received by the hydrogen supplier. The valve and pressure relief device did not show any leaks when the cylinder was pressurized with helium. The supplier believes that on the day of the incident, the cylinder valve was bumped open with the wrench used to remove the cap.
- Other laboratory staff noted that they only heard part of the page to evacuate the lab due to background noise in their labs, but they did evacuate immediately anyway.
- The company maintains written descriptions of how to safely handle compressed gas cylinders in their job safety analysis sheets and their safe work practices handbook. Neither reference prohibited the valve cap wrench being used in the manner it was.
- Visual inspection of the analytical lab was done to confirm that all staff had exited the laboratory, but formal written accountability was not conducted.
- Facilities staff determined that it was not possible to adjust air flow within the analytical lab from outside the lab because all the controls are located inside the lab.
CORRECTIVE ACTIONS:
- Obtain different wrench that provides adequate torque on cylinder cap, but cannot interfere with valve.
- Train staff on how to use new wrench.
- Have staff loosen cylinder caps outside of the building before bringing the cylinder into the lab.
- Install cylinder station outside of the building to hold cylinders with difficult-to-open cylinder caps.
- Update job safety analysis sheet to reflect new cylinder handling procedures.
- Emergency pages should be made twice. For any event that could lead to a fire or explosion, staff should immediately evacuate the area and pull the closest fire alarm box.
- Share lessons learned with other facilities.
- Reinforce with staff the need to check offices, conference rooms, and rest rooms as they are evacuating to ensure that all staff are aware of the emergency.
- Reinforce with incident commanders the need to ensure that formal written accountability is taken during an emergency.
- Investigate the feasibility of relocating critical building controls outside of the analytical lab.