Rupture of a ball mill reactor

The event occurred at a laboratory for hydrogen storage in solid materials. A ball mill reactor containing magnesium silicide under hydrogen atmosphere was over-pressurised and failed resulting in an injury.

The reactor was designed for operation under pressures slightly above atmospheric pressure. In the previous two years, it had been routinely operated under argon and hydrogen pressures in the 5 to 10 bar range but had never been tested for pressures above 10 bar.
A visiting scientist had unsuccessfully attempted to hydrogenate magnesium silicide by ball milling in the 5 to 10 range. Therefore, he attempted to perform the operation at higher pressures. The reactor was loaded in a glove box with 0.5 g of magnesium silicide and six milling balls. When the hydrogen pressure reached 80 bar, the reactor ruptured along the perimeter with a 270-degree crack. The contents of the ball mill were thrown all over the lab. The scientist was injured at the hand kept at the pressure inlet valve near the top to the ball mill, which lifted due to the pressure release.

ball mill reactor

Adding silicium to magnesium is expected to enhance the hydrogen storage performance of magnesium. However, hydrogenation of Mg2Si is hindered by the slow kinetics of the reaction, which can be improved by destabilising the crystallographic structure of the bulk substance for example by high energy ball milling and nanosizing.
[See for example Chaudhary et al., Mg2Si Nanoparticle Synthesis for High Pressure Hydrogenation, J. of Physical Chemistry C, 118 (2013), https://pubs.acs.org/doi/10.1021/jp408650g]

The visiting scientist was taken by ambulance to a local hospital, where the cut was closed with about a dozen stitches. The intern was discharged from the hospital immediately after treatment.

Other laboratory workers heard the noise and immediately administered first-aid. Security, paramedic and environmental health and safety personnel quickly arrived and took charge of the situation.

The H2TOOLS report mentions that the visiting scientist was an experienced researcher in the field of hydrogen storage in materials. Therefore, the laboratory management did not consider necessary to five a formal training in the laboratory procedures and safety measures. However, laboratory work consists in a complex combination of procedures and use of equipment and instruments not necessarily standardised and identical in every laboratory. Newcomers should always be instructed in lab-specific procedures and for a first period supervised when working in the lab.

Moreover, a risk assessment of the lab operations should identify all hazards and provide written instructions clearly highlighting operative ranges, safety limits and the consequences of not respecting them. Warnings must made very visible when handling and using instruments. This approach is critical especially for instruments designed and developed in the lab, it is however valid as well for commercial instruments, the user guidelines of which have to be integrated in the lab procedures.

Finally, these procedures must be reviewed and discussed regularly with all lab personnel to avoid that usage habit and distraction induce lack of attention.