International scientists and engineers are working with reactive metal-hydride hydrogen storage materials in their laboratories. Activities ranging from new materials discovery, to properties characterization, and engineered system development are being performed to develop safe and economically favorable on-board and off-board storage for hydrogen-powered vehicles and stationary applications of the future. The materials must be able to quickly and efficiently absorb hydrogen during the fueling process and then release it appropriately during the duty cycle of the vehicle or stationary system.
Metal hydrides are designed to be reactive with hydrogen gas. This characteristic is also typically associated with reactivity to other gases and liquids, such as humid air. Like any new energy storage technology, the behavior and hazards must be understood and managed to enable safe and effective utilization. Improper storage or use of these materials could result in unfavorable behavior and exposure, so care is needed to maintain a safe and effective operating environment. Most critically, a robust inert gas environment in the form of a laboratory glove box is required to avoid safety events and protect the scientists and their equipment. Ten safety event records in our database illustrate the kinds of incidents that occur and the necessity of careful laboratory practices for handling and operation of metal hydride systems.
Lessons have been learned from these safety events in laboratories where metal hydrides are stored and handled (see alphabetical listing below). Seventy percent of these events are categorized as resulting from equipment failure according to their “owners.” But it’s interesting to note that procedural issues played a hand every single one of them, which may indicate that best practices for working with reactive metal hydrides have not been clearly communicated and understood in some laboratories. Best practices for safe storage and handling of metal hydrides are described in H2BestPractices.
Some of the key lessons learned from these 10 safety events involving metal hydrides are summarized below.
Handling Metal Hydrides
- Do not become careless with handling metal hydride materials, even if you are only working with small quantities.
- Air-sensitive, reactive materials must always be handled in an inert glove box environment.
- Metal hydride materials that are not well characterized should be handled with procedures that assume a “worst case” for that class of materials, intermediates, or precursors.
- Take care with hydride samples that have been disposed; they may contain pockets of reactive material that could become unstable while being handled.
Storing Metal Hydrides
- Minimize quantities of reactive materials stored.
- Store reactive chemicals with regard to their chemical compatibility, and provide secondary containment to prevent contact with incompatible chemicals.
- Consider using plastic containers in place of glass. Sealed glass containers may burst when used to store samples that generate pressure over time.
- Avoid storing metal hydride materials for extended periods of time. Promptly dispose of any remaining material after use.
Shipping Metal Hydrides
- Samples must be shipped according to DOT packing class specifications as found on the material safety data sheet (MSDS). Samples with the potential for hydrogen build-up must be limited to ground shipment only.
- Minimize quantities that are shipped.
- All samples should be properly labeled with hazard warnings on the outside of the package before shipping.
- Provide a description of the packaging with the shipment to enable safe handling by the receiver (e.g., "double-bagged ampoule in inert gas").
- Samples with the potential for hydrogen generation should use a pressure-rated shipping container with head space to contain the maximum possible gas release.
- Shipments of hazardous materials should include the MSDS, standard operating procedures (SOPs), and other safe-handling information.
- Laboratory procedures should be in written form and should be adopted only after performing a safety vulnerability analysis and adopting appropriate risk mitigation steps.
- Protocols for handling metal hydride materials should be incorporated into an SOP and appropriate safety training conducted for all laboratory personnel, including guests.
- Have a formalized procedure in place for neutralizing and disposing of metal hydrides prior to initiating laboratory work.
- Take extra precautions with regards to sealing, leak testing, and vacuum pump type/performance when holding hazardous materials under vacuum for extended periods of time.
- Use digital transducers for measurements. Mechanical pressure gauges tend to be imprecise if only used in a narrow portion of the full scale.
- Ensure that closed containers have adequate headspace and pressure rating for a worst-case incident, or have adequate pressure relief designed into equipment.