• Metal hydride materials of a composition which is not well characterized should be handled with procedures that assume a "worst case" for that class of materials, intermediates or precursors.
• Laboratory procedures should be in written form and should be adopted only after performing a safety vulnerability analysis and adopting appropriate risk mitigation steps.
• Working with small amounts of material does not provide assurance of safety.
• The method described to seal samples that are highly reactive upon exposure to air is not recommended. An alternative method, that is now being used for packaging aluminum hydride samples for offsite shipment is as follows: Aluminum hydride powders (0.5 g - 1.0 g) are sealed in glass bottles with a cap. The bottles are sealed in a thick plastic bag under Ar using a plastic bag sealer in the glove box. The sample bags are then removed from the glove box and sealed under vacuum in a much larger plastic bag using a vacuum sealer. The purpose of the large evacuated bag is to contain any evolved hydrogen gas if the material begins to decompose and the internal bottle & bag rupture. It is a good idea to calculate the maximum volume of H2 (at 1-atm) that could be released by the sample to determine if the outer bag is sufficiently large to contain the evolved gas. The package is then inserted into a cardboard box of sufficient volume (about 1-liter) to accommodate the expanded outer bag.

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.

Recommended Actions:

• The recommended safe storage time for AHF is two years. Contact the vendor for pick up and disposal for cylinders more than two years old. (Unused gas should also be returned, even if it has been less than two years since it was obtained.)
• If the cylinder is less than two years old and there is a desire to keep it, then: Check the pressure of the cylinder. It must be within the maximum pressure stamped on the neck of the bottle. If the pressure is at or above the cylinder's maximum pressure, contact the vendor for pick up and disposal. Do not attempt to move the cylinder yourself.

If below the cylinder's maximum pressure, vent excess pressure through an appropriate medium. Use a two-person team. Conduct venting in a fume hood. Control all ignition sources during venting, since most of the vent gas will be H₂. At a minimum, wear chemical goggles, nitrile gloves, and a lab coat for protection against gaseous HF. Keep an HF exposure kit on hand. An eyewash and safety shower must be readily accessible (within a ten-second travel distance). Any skin, eye or respiratory irritation may be indicative of a possible exposure. Follow the first aid procedures listed on the exposure kit.

In any event, the lesson that should be derived from this incident is the fact that the explosion could have been avoided either by using an inert gas instead of air across the diaphragm, or by monitoring the hydrogen concentration in the upper hemisphere.

As demonstrated by the fire discussed above, lack of adequate maintenance, system monitoring and oversight of maintenance of these facilities can contribute to the ignition of a fire that is difficult to extinguish and poses an extreme danger to fire fighting personnel. Properly maintaining, monitoring and overseeing of hydrogen storage facility equipment can minimize the risk of fire or explosion.

This incident illustrates how a hydrogen fire which appears to be 'quite small' can actually be only the visible portion of a much larger fire. Observation alone is not a reliable technique for detecting pure hydrogen fires and/or assessing their severity.

An important lesson to be derived from this incident is the need to carefully engineer and test all repairs and modifications to high-pressure process equipment.

This incident illustrates how difficult it is to completely purge hydrogen out of a large, complex piece of equipment. Uniform mixing and dilution is unlikely in all the partially enclosed spaces, crevices, etc. If a hazardous operation such as welding must be performed with an air atmosphere (instead of inert gas) in the equipment, reliable gas concentration measurements should be obtained at several different locations. In the case of the generator, a direct measurement of hydrogen concentration may well have been more reliable than the 100 percent CO₂ reading on the densitometer. Furthermore, the gas composition should have been determined at the welding site as well as the top of the generator.

The importance of purging hydrogen piping and equipment is discussed in the Lessons Learned Corner on this website.

This incident illustrates the danger of hydrogen being inadvertently released through blown water seals. Similar incidents have occurred in non-nuclear industrial facilities, but offgas systems present a special hazard because of the stoichiometric proportions of the offgas mixture.

The mechanisms and rates by which hydrogen gas is generated and subsequently accumulated in the holding tank need to be fully understood by vendors and employees alike. Active venting, warning signs, and local alarms designed to activate when hydrogen ventilation lines are obstructed are essential.

The above described events are an indication of a potential licensee/vendor interface problem. Based on the information received, the vendor was not completely informed via the purchase specifications regarding the service condition to which the valve would be exposed. Further, all users of these valves were not notified of the initial problem through either oversight by the vendor or as a result of the valves being supplied through an intermediate source. To avoid similar incidents in the future, onsite personnel need to ensure that their vendors receive comprehensive specifications relating to the application, use and service conditions associated with all of the stainless steel valves implemented in applications susceptible to hydrogen embrittlement.

A web-based resource developed by Sandia National Laboratories to provide data on hydrogen embrittlement of various materials is available at Technical Reference for Hydrogen Compatibility of Materials.

The hydrogen facility does not meet industrial guidelines for facilities of this type, from the standpoint of (1) the separation distance needed between a hydrogen pipe break and the building ventilation intake to prevent buildup of a flammable or explosive gas mixture inside the enclosure, and (2) the separation distance needed to prevent damage to safety-related structures resulting from the explosion of an 8,000-scf hydrogen tank.

Safety concerns such as hydrogen leaks and storage tank detonations must be considered and used to create effective new construction designs which mitigate the consequences of such events. Existing buildings which house hydrogen storage tanks need to properly analyze all of the risks associated with the use and storage of such systems.

This incident highlights the need to properly design safety interlocks. These safety interlocks need to be carefully incorporated into the initial building/plant designs and should consider all of the unexpected occurrences, such as the electrolysis cell bank losing power in this case, and the potential ramifications of such occurrences.

The investigative report noted that the explosion could have been prevented by (among other things) a continuous gas analyzer test of oxygen and hydrogen product purity. The continuous analyzer should be interlocked to shut the electrolyzer down when product purity falls below some nominally critical values. This incident, illustrates the need for more widespread use of hydrogen analyzers, and the inverse relationship between hydrogen accidents and regular maintenance.

The lessons of this event fall into five categories: (1) proper in-plant communications during events, (2) proper valve application for use with hydrogen, (3) excess flow check valve set point, (4) heating and ventilation and air conditioning (HVAC) maintenance and flow testing, and (5) hydrogen line routing. The operator is examining ways to improve communications in the plant during events and the training of personnel in reading portable instruments.

As another corrective measure, the operator is examining the use of other types of valves, such as valves with a diaphragm or bellows rather than conventional stem packing, in lines containing hydrogen. The operator is also examining the set point for the excess flow check valves on the hydrogen lines. These check valves are designed to limit the flow of hydrogen in the event of a large leak so that when combined with proper ventilation in rooms with hydrogen lines, hydrogen levels would remain within specified limits throughout the plant.

This plant had HVAC flow balancing problems during the preparation for plant startup. Generally HVAC flow balance is based on the heat loads and the resultant room temperatures under normal and accident conditions. However, this event demonstrates that hydrogen concentrations also may need to be considered to set a lower limit on the ventilation in rooms that contain hydrogen lines.

These events show the importance of preventing combustible gas mixtures from accumulating in piping. In both of the above described events, hydrogen and oxygen gases apparently accumulated to a combustible level which then catastrophically failed these piping systems. Proper venting or other considerations to prevent accumulation of combustible gases in piping high points might alleviate conditions leading to hydrogen combustion.

Work documentation (work orders and baseline drawings) should reflect the current system configuration.

Recommendations

1. Develop procedures for temporary change configuration control of high-pressure systems. The overall work process should be included in one work authorization document.
2. Re-emphasis to all personnel that current procedures be followed. If the work order is not written to reflect the current system configuration, stop work, revise work order, and have the work order properly reviewed prior to continuing work.
3. Write a procedure for proper clamp removal and installation and train technicians to the procedure.

Batteries stored on a charger can explode during use if overcharged.

Recommendations

1. Use automatic current limiting or timed circuit chargers when charging batteries.
2. Operators should be aware of safe practices and proper battery charging instructions.

Personnel should be properly supervised, and supervisors should be aware of the activities of their personnel. Personnel must be motivated to adhere to established policies and procedures. All personnel associated with potentially hazardous work should receive necessary safety training.

• Battery power supplies require adequate ventilation for all operations, or the battery box should be designed to:
  • Eliminate all sparking devices
  • Ventilate during charging operations
  • Provide inert gas purge and pressurization methods, and
  • Provide adequate pressure relief
• Give consideration to other power supply methods.
• Organizational operating procedures and staffing should as necessary ensure that all equipment designs and work procedures are reviewed by an independent engineer. When hydrogen equipment and procedures are modified, the changes should be reviewed.
• Safety manuals should be revised to incorporate information on storage battery handling and operations safety practices. Safety expertise should be made convenient. Provide adequate training.

Immediate Corrective Actions

1. Fuel cell test stand was shutdown and sent to manufacturer for investigation.
2. Carbon dioxide fire extinguisher installed in laboratory.
3. Formal process hazard review performed

Long-Term Corrective Actions

1. Replaced all flexible tubing in test stand with stainless steel (316).
2. Replaced water knockout device with latest manufacturer's design on both the H₂ and O₂ lines to reduce the risk of gas flame by leached catalyst.
3. Installed a “High-pressure trip – Carbon dioxide” fire suppression system in the lab.
4. Installed a redundant hydrogen detector inside the test stand.
5. Installed an external hydrogen delivery system with stainless steel feed lines into the lab.
6. Revised the Standard Operating Procedure for the fuel cell test stand.