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.

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.

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.

Disable the fueling process if the operator does not follow the proper sequence of steps in the fueling procedure. Improve the fueling procedure to make it inherently impossible for the sequence to be done improperly with the same result.

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.

Lessons Learned The site initiated the establishment of a field patrol and strengthened their onsite monitoring of mechanical equipment during a plant-wide temperature rise.

• Quantitative control of tightening torque on bolts should be carefully executed at all high-temperature and high-pressure plants.
• A plant must pay close attention to both the chemical impacts and the mechanical impacts of an unexpected temperature rise during start-up operations.

Several factors are important for flange use in applications of this type. Bolting patterns/torque order need to be considered in engineering, training, stewardship, and maintenance aspects of the specific operations. Cold bolt torque requirements should be developed so hot bolting is not required or relied upon for start-up. Flange stress from an increased or decreased operating temperature needs to always be checked. Substantial industry knowledge and practice exist for flange use to ensure that such operations are conducted safely.

Lessons Learned
Construction errors are difficult to detect once construction is complete. It is important to develop and use a systematic oversight process for minimizing construction errors during the construction process.

Countermeasures

• Thorough control of component parts during the construction process is required.
• Bolts should be tightened equally and fully.
• A new support for distributing the weight of piping is installed.
• Thoroughness of checks after construction is going to be initiated.

Additional discussion about working with reactive metal-hydride materials in the laboratory can be found in the Lessons Learned Corner on this website and in the Hydrogen Safety Best Practices Manual.

Although a functional fire protection system would have helped to extinguish the fire, a properly installed hydrogen detection system, coupled with a properly designed ventilation system, could have prevented the incident altogether.

Hydrogen rises twice as fast as helium, at a speed of 45 mph. Therefore, unless a roof or some other structure contains the rising gas, the laws of physics prevent hydrogen from lingering near its point of production. It is unclear weather the room's ventilation system wasn't functioning properly, or if it wasn't designed properly; but in either case, battery charging facilities need to consult experienced engineering firms on proper location and design of hydrogen detection and exhaust systems. On-site Standard Operating Procedures also need to mandate periodic functional/operational tests.

Adequate ventilation of battery charging facilities is addressed in the Lessons Learned Corner on this website.

Routine maintenance activities on pressurized hydrogen systems should be conducted per written design specifications. The procedures should provide detailed oversight regarding bolt, nut and fitting replacements or repairs. A formal review process should be required to ensure that the maintenance was performed according to the written specifications, and that the hydrogen system will continue to function as designed until the next scheduled maintenance activity.

This incident emphasizes the need for proper gas detection and ventilation systems, as well as fire suppression systems, in laboratories using and storing hydrogen. This is especially true when open flame burners are in close proximity. Experienced consultants/engineers should be involved in the design of gas detection and ventilation systems before hydrogen cylinders are employed in any laboratory. Laboratories also need to develop a Standard Operating Procedure, requiring periodic maintenance on hydrogen systems to check fittings, valves, and all critical components to ensure proper functionality at all times.

Hazards should be eliminated to the extent possible rather than depending on workers to follow an operations manual.

Potassium carbonate draw-off operations should be improved, and the operations manual should be revised. The manual should be reviewed by workers before maintenance activities are started. Training on mandatory compliance with the operations manual should be carried out for all staff involved in hydrogen plant operations and maintenance.

Fail-safe position of control valves in supply lines must be set correctly to prevent damage to pressure vessels.

Recommendation

Set all valves for fail safe operation (open or closed) according to needs before installation in pressure or vacuum systems.

1. The dilution water for making a polythionic acid aqueous solution was changed from industrial water to pure water to lower the chlorine concentration in the piping.
2. Water that accumulated in the drain was removed before heating began. Steam tracing was strengthened to prevent condensation of moisture.
3. The gusset was remodeled into a structure in which thermal expansion is not restricted.

Careful management oversight of startup procedures is necessary to avoid stress corrosion cracking from occurring in hydrogen piping, since it can result in a serious accident. The chlorine concentration can be high in industrial water, and it is desirable to avoid treatment using water with a high chlorine concentration.

1. The plant tried to increase production and decrease workload, but failed to notice the potential negative outcomes of this change.
2. It is necessary to thoroughly simulate all potential negative outcomes of a change in procedures.
3. Although a valve stops a flow, it is necessary to consider potential leakage. A valve might leak due to fouling, solid material between seals, etc.

• Operation and management of the hydrodesulfurization unit should be strengthened to account for abnormal phenomena such as local corrosion.
• The safety review system for remodeling existing equipment and facilities should be strengthened.
• All refineries with the same kind of desulfurization units should thoroughly check dead-end piping areas. They should also conduct a safety review of their operating and management procedures.
• If a very careful study is not done, safety aspects of remodeling projects might be disregarded, even if the initial purpose of remodeling is achieved.
• Dead-end piping is the cause of various problems, so careful attention to areas of dead-end piping is needed to ensure safe operation.

• Verify that all PRDs contain fuse-backed adapters.
• Explore elimination of rupture disk PRDs and substitution of spring-style relief valves.
• Develop new hydrogen unloading procedure using a written checklist. * Add instrumentation to monitor the high-pressure hydrogen system.
• Confirm that temporary offices/facilities are not co-located with hazardous chemical storage sites.
• A procedure is now in place that requires a Job Hazard Analysis (JHA) to be done on unloading hydrogen and shared enterprise-wide.
• A competent plant employee must be present during all hydrogen unloading activities.

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.