Mechanical pressure gauges tend to be imprecise if only used in a narrow portion of the full scale. Digital transducers, although slightly more expensive, offer much more precision. The event happened because the set pressure was only 10% of full scale, and the error of the mechanical gauge was over 5%.

While this is not the reason for the event described, control of the charging pressure is one of the most crucial parameters. Although the storage is at low pressure, the pressure increase upon temperature increase can be much steeper than the ideal gas law would predict, depending on the charging conditions.

The chosen trigger point of 35 bar for the pressure relief valve is very low. Based on the tank design, at least 60 bar would be acceptable.

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.