Mounting hardware incorporated polymeric braces not suitable for long-term exposure to sunlight and temperature extremes. With time, the polymeric materials had disintegrated, allowing the mounting brackets to become loose. In addition, the mounting brackets were all oriented with a degree of freedom in the same direction such that drag forces from strong wind coming from just the right direction were able to dislodge the vent line and blow it down. Periodic inspections and maintenance operations failed to pick up the deteriorating hardware.

Hardware design must be adequate for weather conditions and materials selection must be compatible with temperature excursions and solar-UV exposure conditions. Operations must include periodic inspection of mounting hardware.

Emergency procedures must address conditions that include the presence of a hydrogen leak that may pose a hazard to personnel attempting repair operations. Procedures were developed by:

• Determining the approximate temperature and release rate of the hydrogen emanating from the damaged vent,
• Finding computed hydrogen dispersion information based on diffusion and wind (see combustible cloud length as a function of release rate in Edeskuty, Frederick J. and Walter F. Stewart, Safety in the Handling of Cryogenic Fluids, Plenum Press, New York, 1996), and
• Using the dispersion information to establish a safe working area for repair operations and an exclusion zone around the hydrogen release point.

The possible outcomes from new maintenance scenarios can be predicted by using an accurate simulation. The proposed filter change-out maintenance was studied to identify conditions to which the catalyst might be exposed and a mock-up of the filter, it's mounting/housing, and catalyst was assembled. Conditions selected to represent the worst case that could be encountered during a maintenance operation were reproduced. For the conditions of temperature and pressure, this included simulating the state of the catalyst. Oxygen was removed from the catalyst with a dry nitrogen purge, and followed by a graduated hydrogen purge from 0.5 to 10 % concentration. Hydrogenation was completed by then subjecting the catalyst to a purge of 100 % concentration of hydrogen. De-ionized water was vacuum-degassed for 10 minutes to remove oxygen, then saturated with hydrogen (by bubbling) at pressure. The simulation of pre-change-out filter conditions was completed by adding the hydrogen-saturated water to the hydrogenated catalyst within the mock-up system. The simulation of conditions introduced by the proposed maintenance was accomplished by draining the water and introducing a purge of oxygen-enriched air (ISS ambient conditions). The drained water and purged air were captured for laboratory analysis to check for thermal degradation and toxic byproducts of Teflon. Gas Chromatography with Mass Spectral detection (GC-MS) revealed no fluorinated species above the detection limits in the gas phase, and Ion Chromatography (IC) identified only small amounts of fluorinated compounds in the liquid phase (not indicative of a handling hazard). Post-test thermal gravimetric analysis (TGA) of samples indicated that insufficient heat was generated in the tests to thermally decompose the Teflonized catalyst. The conclusion is that when charged catalyst is handled wet, reactions with air are reduced to the point of permitting safe handling. A caution is noted. While deliberate simulation of conditions that would result in rapid exposure to dry charged catalyst was not performed, the hydrogenation step, if not initially done gradually, but with 100 % concentration hydrogen, will produce smoke and steam, suggesting any procedure that introduces rapid exposure to air could result in high temperatures and potentially hazardous by-products.

Maintenance on PEM technology systems that involves accumulated catalyst within filters may be safely performed by reducing the rate of exposure of catalyst materials to air or oxygen, always keeping a coating of water on catalyst surfaces and making sure discarded catalyst is properly disposed and not allowed to dry out, especially in the presence of volatile and flammable materials. Catalyst materials exposed for a time in a hydrogen environment will absorb substantial amounts of hydrogen, becoming "activated". Subsequent exposure to air or oxygen without mitigating steps can cause high temperatures to occur on catalyst surfaces, creating a potential fire hazard. Do not expose Teflon to high temperatures.

1. Hydrogen safety training should be provided to local emergency responders.
2. Liquid hydrogen installations should be inspected by facility personnel on a frequent basis, consistent with NFPA 55, to verify proper operation and inspect for physical damage or leaks. If there are problems, contact the servicing company immediately.
3. Industrial gas companies that design, install, and maintain liquid hydrogen installations should follow the guidelines set in the Compressed Gas Association (CGA) publications: G-5.4 - Standard for Hydrogen Piping Systems at Consumer Locations, G-5.5 - Hydrogen Vent Systems, H-3 - Cryogenic Hydrogen Storage, and H-5 - Installation Standards for Bulk Hydrogen Supply Systems.
4. Burst disks are highly sensitive to any form of back pressure.

The SS 24-inch pipe that failed was replaced with 1-1/4 Cr 1/2 Mo alloy pipe that is corrosion-resistant to SCC. A revised HTS bypass piping layout was installed to prevent the hazardous conditions that lead to the failure. A detailed hazard review and evaluation of all of the materials of construction in the hydrogen plant process gas system led to preventively changing several other pieces of piping and equipment items in the SMR process to 1-1/4 Cr 1/2 Mo.

1. Redundant safety systems prevented this event from becoming an incident. The 1%-hydrogen-concentration-level-triggered fan was backed up by a 2%-hydrogen-concentration alarm. The alarm is continuously monitored (24/7) by a remote Network Operations Center (NOC).
2. Since this event, a pressure switch has been added to alarm in case of a fan failure and is also continuously monitored by the remote NOC.
3. Future standards will require two ventilation fans, one running continuously and the other triggered to start when a 1% hydrogen concentration is reached.

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

To prevent a similar flashback, the following measures have been taken:

1. The valve is opened slowly to avoid a major leading shock into the venting line.
2. A special nozzle (Laval or similar) is mounted directly after the opening valve. This prevents shock reflections from entering the premixed zone.

Many accidents reported from paper mills have much in common with this incident. Microorganisms in the process water with pulp produce hydrogen gas that mixes with air to form an explosive atmosphere. The ignition source is typically sparks produced by hot work, but ignition by electrostatic discharges in a cloud of mist in a storage tower has also been reported (see Explosion Caused by Microbial Hydrogen Formation).

Provided the hazard posed by bacterial hydrogen production has been recognized, there are several preventive and/or mitigating measures that can be considered for reducing the risk:

1. It is advantageous to avoid anaerobic and stagnant conditions in the solution by providing sufficient circulation and/or aeration (bubbling air through the solution), but this requires monitoring and could result in foaming or generation of biogas.
2. The formation of an explosive atmosphere may be avoided by providing sufficient natural or forced ventilation to keep the hydrogen concentration below the lower flammability limit (LFL), or by using an open-top floating roof tank to remove the space where an explosive mixture could form.
3. Forced ventilation can be used, but this solution requires monitoring, and care must be taken to avoid introducing a potential ignition source.
4. The free space above the liquid level can be blanketed with an inert gas to prevent the formation of an explosive mixture, but this is a relatively expensive solution that requires monitoring, and the inert atmosphere will promote anaerobic conditions that favor bacterial hydrogen production.
5. Strict enforcement of hot work procedures, including gas measurements and the use of non-sparking tools, may prevent certain ignition sources, and especially those that are directly associated with personnel risk.
6. Technical solutions such as grounding to prevent build-up of electrostatic charges and installation of flame arresters on all openings in the tank to prevent ignition by lightning, etc. can also reduce the risk, but the possibility of having an explosive atmosphere inside the tank should still be regarded as a severe hazard.
7. Risk management strategies should include a continuous focus on preventive maintenance, mandatory safety training for all workers, regular reviews of risk assessments, and learning from previous accidents in related industries.

A tool is provided for removing the cylinder cap that cannot contact the valve.

Consider design review of all adapter fittings.

Several best practices resulted from this incident and will be implemented if similar circumstances present themselves in the future.

• Close bay door.
• Keep within proximity of bay.
• Be aware of other bays operating with open doors.
• Notify others in the area of venting hydrogen.
• Have at least two knowledgeable people present when working.
• Secure an isolated tank that is not in a vehicle.
• Provide a vent stack routed to a safe location if possible.
• Use a de-fueling port if available.

A new best practice resulted resulted from this incident. It states that before any work is started, a third party should verify with a visual inspection that the actual equipment to be used matches the planned equipment list/protocol.

1. Place signs on all liquid hydrogen tanks indicating that no water is to be put on the vent stack.
2. An additional secondary backup vent stack was added to liquid hydrogen tanks. This secondary stack is designed to be used only if needed in the event the main vent stack becomes plugged with ice, such as what occurred in this incident. The main vent stack is still the primary means of venting all relief devices, rupture discs, and any normal venting of hydrogen. The secondary vent stack would only be used if the main vent stack failed.

All installed and certified safety and emergency systems functioned as designed.

1. The fuel cell turned off immediately after fire detection.

2. The fire suppression system was immediately initiated thereafter.

3. The physical separation of the batteries, the fuel cell, and the hydrogen tanks prevented the fire from spreading. This separation was developed from the FMEA of the ship and hybrid system.

4. No hydrogen leaked (i.e., the physical separation worked). However, direct fire contact or overheating of the hydrogen tanks would lead to a controlled automatic discharge of hydrogen outside the vessel.

5. The CO2 fire-fighting system in the battery room was activated for fire suppression. However, the hatch was left open by the battery supplier for the test run, which reduced the effectiveness of the suppression.

Several procedural and design changes should be considered for the future:

1. Replace the use of pure hydrogen with a 95:5 mixture of nitrogen and hydrogen to reduce the possibility of an explosive atmosphere occurring. Laboratory personnel should check each tank that is delivered to ensure that the gases are present in the proper ratio.
2. Adhere to the manufacturer's recommendations for operation of the anaerobic chamber.
3. Following the check of the lines to make sure all the connections are tight, all gas cylinders should be closed; then, only the desired gas cylinder should be opened for use.
4. Use of "T" connections between gases should be eliminated. If there is continued use of a "T" connection, only connections with a toggle switch to limit the introduction of gas from a single cylinder should be used. No exceptions, even on a temporary basis.
5. The laboratory should continue to investigate the availability of hydrogen and/or oxygen sensors with the hope of finding some that can withstand the corrosive atmospheric environment.
6. All laboratory personnel should receive refresher training that includes standard safety precautions as well as a more detailed review of the hazards of working with hydrogen. Hydrogen use in anaerobic chambers is discussed in the Lessons Learned Corner on this website.

The turbine components that caused the vibrations were a retrofit design which had been in service for about two years and were under warranty from the vendor. The root cause analysis of the event determined that the damage was caused by a defect in the design or assembly of the turbines.

Recommendations:

1. The using organization should define necessary activities in order to place hydrogen systems in long-term periods of inactivity. The defined activities should address requirements for rendering inert, isolation (i.e., physical disconnect, double block and bleed, etc.) and periodic monitoring.
2. The using organization should develop a process to periodically monitor hazardous systems for proper configuration (i.e., a daily/weekly/monthly check sheet to verify critical purges are active).

Although the preparation-for-transport procedures were done the same way they were done for previous outreach programs, this time it proved to be a different situation. It is not clear what caused the ignition of the first balloon, which then set off a chain reaction to the others. The incident shows that preparation for transport is a very important element in the overall process, and it should be evaluated for risk factors along with every other element of the process.

Safe storage and transportation of balloons filled with a hydrogen-oxygen mixture is a very risky undertaking. There are few scenarios that do not involve enclosed spaces (e.g., a car) and the potential for static discharge. Perhaps a mesh bag would work, as long as sufficient ventilation is ensured. Nonetheless, using lecture bottles and filling balloons on-site seems to be the safest method. Yet if the floor in the demonstration area were carpeted, enough static could be generated to ignite a balloon. The demonstrator's greatest fear is that a child might ask to participate in the demonstration, then reach out to touch the balloon and have it detonate in their face.

The demonstrator feels fortunate that his injuries were relatively minor (no respiratory damage). He urges that a full risk assessment be performed prior to balloon storage/transportation and setup/performance of this type of science demonstration. Guidance for undertaking a hazard analysis and risk assessment can be found in the Hydrogen Safety Best Practices Manual.

• Active GH2 sensors should be installed and continuously monitored in all enclosed buildings near GH2 sources. All buildings near areas where hydrogen is used should be designed to preclude GH2 entrapment (e.g., sloping roof with ventilation at the highest point).
• Underground carbon steel lines beneath concrete pad areas should not be used for GH2 transmission. All GH2 lines are now stainless steel and above ground. - Any GH2 transmission lines buried underground should be proof-tested and leak-checked on a periodic basis.
• Any below-grade piping installation should be in open trenches covered by grating.
• Facilities should be protected from GH2, at a safe distance, by manual isolation valves. If remote-operated valves (ROVs) are required for operational isolation purposes, the ROVs should be in series with and downstream of the manual isolation valve.
• The pressure between isolation valves and stand shut-off valves should be routinely monitored on a daily basis.
• Field repair of mechanically severable valves in high-pressure systems should be eliminated.
• Valves repaired in the field should be subjected to functional and leak checks, including actuator and valve seals at simulated operating conditions. A written procedure should be prepared and used.
• Valves utilizing pneumatic actuators should have actuator piston and piston nut staked (or locked by other positive means) in the installed condition.
• All high-pressure gas lines scheduled to be inactive for periods greater than 6 months should be physically isolated by blind flanges from active systems.
• Supply system status of pressure vessels and lines (pressure and/or quantity) should be recorded at the start and completion of operations each day. All reservoirs should be isolated at close of business each day, and before weekends and holidays.
• Corrosion protection systems for underground lines should be reviewed and tested to confirm the adequacy of the systems.
• Operational and support buildings at hazardous sites should be isolated (i.e., interconnecting air conditioning systems should be avoided). Buildings connected to hazardous sites by tunnels and/or conduits should be physically isolated by seals. If physical isolation is not practical, then positive air flow should be maintained in tunnels and conduits.
• Explosive gas detection meters should be included in the equipment carried by firefighters and emergency medical personnel.
• Fire alarm transmitters should be located at all hazardous locations.
• Emergency instructions for isolating GH2 and utilities for hazardous locations should be permanently posted with names and telephone numbers of key individuals to be contacted.

The incident resulted from an inadequate design for the storage location of the copper gas supply tubing (too close to an electrical outlet). The gas supply tubing was too long for its intended purpose and posed a hazard in its coiled state near the outlet. This near miss had the potential for more significant damage/impact to the facility and to the researcher because of a hydrogen gas supply line also in close proximity to the same outlet.

Laboratories should be inspected to ensure that gas supply lines are protected against electrical exposure in the following manner:

1. Limit the amount of copper tubing to the length that is necessary to reach the intended equipment.
2. Secure gas supply lines to the wall and/or counter top in a way that will prevent electrical exposure.
3. Perform visual inspections for loose lines before removing electrical plugs from outlets.
4. Ensure that there are no exposed energized parts of electrical circuits or equipment near your compressed gas systems.