A vacuum containing hydrogen gas, created by the reaction of aluminium powder with water, exploded and burned a worker, a court heard.
The 27-year-old employee of Staffordshire research and development company, Renishaw plc, suffered burns to the top of his body and spent two weeks in hospital recovering from his injuries.
The company carries out a laser-melting process, which uses focused laser energy to fuse metallic powders into three-dimensional objects – an emerging manufacturing technology with applications in the medical industry, as well as the aerospace and hi-tech engineering and electronics sectors.
The specialist industrial vacuum, more commonly used to clean up wood dust, had been used to clean up waste aluminium powder created during the manufacturing process, before being left to stand over a weekend. The powder reacted with water used in the machine and created hydrogen gas, which exploded when the unassuming worker switched it on.
The HSE launched an investigation into the incident, which occurred on 6 February last year at the company’s Whitebridge Park site in Stone. It concluded that had Renishaw undertaken a proper risk assessment, it would have identified that the metal powder mixing with the water inside the vacuum cleaner could cause a reaction and a risk of explosion.
The company was served a Prohibition Notice in relation to the use of the machine to clean up metals that could cause an explosion risk. The firm no longer uses the device for such a purpose.
Pleading guilty to breaching reg.5(1) of the Dangerous Substances and Explosive Atmospheres Regulations 2002, Renishaw plc was fined £7000 by Stafford magistrates on 27 March. Costs of £6397 were also levied.
Speaking after the hearing, HSE inspector Wayne Owen said: “This type of vacuum was not suitable for use with aluminium powder. Had the company paid attention to the instructions for working with this metal powder, or indeed the machine itself, then the incident could have been prevented.
“It must have been a very frightening experience for the worker, who suffered painful injuries. Aluminium powder mixed with water can create highly explosive gas, and a suitable and sufficient risk assessment would have shown that they should not have been mixed.”
The employee was off work for three months, but a spokesperson for Renishaw told SHP he had made a full recovery and had returned to the company, working in the same role.
Emphasising that it is the first time the firm had been the subject of an HSE prosecution, he added: “This was a unique incident, but clearly we admitted responsibility and worked very closely with the HSE, and we were commended by the magistrates for the work we’ve done [following the incident].”
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