Shutoff valve location and/or redundant shutoff valves at storage vessels are important for containment to prevent escalation.
Consider design features within equipment skids to reduce the likelihood of cascading events.
Pressure-switch component replaced with better design.
Component listing standards are important to further development/deployment of this technology.
Consider improving leak/fire detection and shutdown systems.

1. Provide additional retraining of operators. Curriculum should emphasize the proper response to high oxygen in the hydrogen gas.
2. Evaluate current knowledge of operators. Operators should know proper response, such as contacting engineering or management support as needed, to evaluate any potentially dangerous process conditions they might observe.
3. Revise interlock strategy. The plant control system was reviewed and enhanced with additional interlocks that automatically shut down the process and safely secure the hydrogen systems on certain pH levels and certain oxygen levels.

1. Train personnel on delivery procedures and emphasize the safety aspects of hydrogen connections and disconnections, and verification of clearance for trailer movement prior to departure.
2. Provide site-specific delivery procedures and possibly include a checklist as a reminder of key safety items prior to departure.

1. Defects in equipment, such as welds, may not be evident during initial proof testing and operation.
2. When an equipment defect is found, check equipment for possible similar defects in other areas of the equipment.

Manuals showing the correct connecting and disconnecting procedures were established for each fueling dispenser. Separate manuals were needed since the shape of the grip differs from dispenser to dispenser.

Follow CGA G-5.5 vent end system designs.

A step was added to the laboratory procedure in which all catalyst waste is thoroughly dampened with water and sealed in a plastic bag before being placed into a waste container.

Safe work procedures will be prepared and followed. Hydrogen will be vented out of the system to create an inert atmosphere before working on system tubing and joints. The importance of purging hydrogen piping and equipment is discussed in the Lessons Learned Corner on this website.

1. Maintenance work scopes must be adhered to. If added work is approved, it must be tracked and reviewed to ensure that the equipment is inspected by operations personnel. Scheduled work and extra work should be listed and checked off for proper line-up.
2. When closing valves, ensure that they are closed completely. Bull plugs must be installed tight enough so that they will not loosen as a result of contraction/expansion occurring during hot and cold cycling and/or compressor vibration. When closing a valve, a valve wrench must be used to synch up by using force to turn the valve handle a 1/4 turn. When installing a bull plug, a wrench must be used to ensure that the bull plug is tight.
3. The recommissioning process used to reactivate the gas oil hydrotreater unit was modified to address bull plugs. Involve plant operations and health/safety personnel to develop an operational mechanical integrity checklist to ensure that all mechanical equipment components are addressed and then train personnel to use the checklist.

Investigation determined that internal galling has caused the failure rendering the needle valve unusable. The galling was caused by a stainless steel stem acting against a stainless steel seat. This failure mode had been observed before and the manufacturer had been previously notified. The valve was replaced with a new needle valve to continue with the test program. Additional discussion of best practices for equipment maintenance and integrity can be found in the Hydrogen Safety Best Practices Manual.

For the use of mechanical fittings in hydrogen service, administrative controls should be in place, as in this case, to ensure that leak testing is conducted on a regular basis. It should never be assumed that every fitting is tight. Additional discussion of best practices for fittings and joints can be found in the Hydrogen Safety Best Practices Manual.

Failure of a diaphragm is not infrequent, but the seizure of the main nut threads is very rare. The manufacturer claimed this had never occurred before with this type of unit. The broken plunger is likely the result of poor instructions/communications between the vendor and the user. The detail and quality of drawings provided by the vendor were poor given the level of investigation and repair needed for this occurrence. It is possible that the proprietary nature of some equipment information may have been a factor.

The visiting intern had several years of experience in research projects and tasks that were similar to those in progress at this laboratory. This led to the incorrect assumption that formal introductory training for this laboratory was unnecessary. Steps should always be taken to ensure that anyone working in an unfamiliar laboratory setting is properly trained.

It is important to have written operating procedures for the use of laboratory-scale equipment involving hazards or risks of this nature. Operating procedures should also document any equipment parameter limits. Such procedures should be reviewed with all personnel as part of their laboratory training before they perform any experiments.

More information on management of change can be found in the Lessons Learned Corner and also in the Hydrogen Safety Best Practices Manual.

After the aforementioned incident, a rigid cage was designed to protect the reactor from external conditions, and to protect the contents of the hood and any experimenter from the reactor, in the event of a pressure burst from the reactor cell. Additionally, the experimental setup was redesigned to include only electrical distribution that has been verified to be in compliance with National Electric Code and that is located outside the cage. Further, the experimental setup has been redesigned to include a hydrogen supply line shutoff, so that if the pressure reactor cell integrity is compromised, the hydrogen supply is shut off. The fume hood has been fitted with a hydrogen sensor. Lastly, researchers were reminded that hydrogen experimental setups should be verified by another person, and hydrogen-involving experiments should be carefully monitored.

Hydrogen development work is inherently hazardous, and greater precautions than the norm need to be taken to ensure a safe work environment.

High-pressure fueling hoses should be examined daily for signs of external damage, including corrosion, abrasion, cuts, and kinking. High-use fueling hoses should be replaced every six months.

1. Revise fire protection operations surveillance tests to include a maximum of 110% of the agent net weight to prevent over-filled cylinders from being placed in service.
2. Identify cylinders currently in service that exceed the 110% maximum allowable limit, remove them from service, have them inspected and refilled to the new criteria, and then return them to service.
3. Purchase new compressed gas pilot control cylinders.
4. Revise the plant industrial safety program to enhance cylinder storage requirements by eliminating the use of ropes as restraints.
5. Purge the gas storage shed of all non-related storage, secure all cylinders with chain, fabricate cylinder racks for small cylinders, and eliminate storage of items next to the hydrogen system emergency manifold.
6. Conduct a probabilistic safety assessment of the possibility of missile hazards from compressed gas cylinders.
7. Change from the current CO2 vendor to another qualified service vendor.
8. Investigate whether a breakdown of the fire protection QA program occurred.

• The fuel cell vehicle that was involved in the accident has been retired. The fuel cell power plant from that vehicle has been removed and is being used in another fuel cell vehicle.
• The fuel cell vehicle accident reinforced the need for training of drivers, supervisors and emergency response personnel. As an action item, this project team will conduct refresher training courses for the drivers and local emergency response personnel. The project leads conducted training classes on hydrogen safety and incident response for local emergency response personnel; including the local fire department and the police prior to vehicle deployment and the station opening. A significant learning by this project team is that emergency response agencies are subject to frequent personnel changes. As such, training should be repeated periodically.

An investigation team was formed to determine the cause of this anomaly. The team performed a fault tree analysis which identified the following five main paths or gates: fault in the original weld, age, component not built per design intent, overstress, and design error. This led to 48 events on the fault tree, all of which were investigated. The investigation, analysis and testing determined that the first path, fault in the original weld, was the primary source of the failure.

The fault tree analysis pointed to three probable and two possible contributors of the failure. The probable contributors included incorrect filler rod selected by welder, insufficient fusion in the weld, and insufficient weld penetration. The possible contributors included incorrect power level setting and incorrect heat level applied during welding.

Materials laboratory work confirmed that improper filler metal (4043 Al) was used to weld the 5083 Al alloy vent pipe. The 5083/4043 combination is not recommended for Al welding per either current or past standards. In addition, the failed weld was a very poor weld, most likely a field weld. NDE data indicated a higher number and severity of defects in this weld compared to other welds in the vent line. According to the material lab's failure analysis report, the weld failure resulted from tensile overload originating at the bottom surface of the vent line during tanking operations and was likely the result of a single overload event.

Vent line inspection was performed to identify other suspect welds. Inspection methods included the following: visual inspection, conductivity tests on both sides of each weld to identify the pipe metal (5000 or 6000 series Al), helium leak check of welds, non-destructive evaluation (NDE) using a combination of x-rays and ultrasonic testing, and silicon etch tests to identify weld material. The silicon etch test procedure was successfully developed in the course of this effort to identify 4043 weld filler material in the field.

Instrumentation attached to vent lines during subsequent operations has provided data for the ongoing weld stress analysis and screening criteria to determine which welds required clamshell repairs. Weld defect growth/propagation can now be monitored at periodic intervals.

An unexpected temperature difference of ~200 deg F between the top and bottom of the piping was found to occur during tanking operations in the same area of the failed weld. This temperature difference was responsible for the high thermal stress seen there. Data indicates that the peak stress in that pipe section occurred at about the same time that the weld failed and was higher than predicted.

The combination of the cold water temperature (reducing the fatigue strength of the bolt), and the abnormally high number of cyclical stresses imposed by the imbalance from the hydraulic system check valve failure resulted in the failure of the fasteners.

Proper installation of check valves and other equipment should be visually inspected prior to pressurization.