RR1177: Risk control for small pressure vessels: café boilers, bench-top autoclaves, and model steam engines
Café boilers such as espresso machines are widely used small steam-based pressure vessels, for instance in the hospitality and service sectors. Bench-top autoclaves and miniature steam engines are small steam-based pressure vessels widely used in schools and other educational settings. Duty holders must have effective risk control measures in place to prevent vessel failure and protect the public and workers. Legal requirements are in: the Provision and Use of Work Equipment Regulations (1998), the Pressure Systems Safety Regulations, PSSR (2000) and the Pressure Equipment (Safety) Regulations (2016). Control measures include: correct operation, regular inspection, testing and maintenance. However, there was a lack of engineering evidence about the potential for failure of these small vessels in order to determine proportionate risk controls.
This report describes experimental research on a sample of café boilers, bench-top autoclaves and miniature steam engines. The aim is to understand: (i) the safety devices installed and (ii) the failure modes that could occur if the vessels’ safety devices failed. The researchers used a sample of new and second hand vessels. They carried out metallurgical inspection and over-pressurisation of the machines. The researchers identified that overheating and/ or overpressure could result in catastrophic vessel failure and an explosive release of energy with flying fragments and scalding steam and water. This has the potential to cause significant injury or death to people in the vicinity. However, the researchers consider that if effective control measures are in place, catastrophic vessel failure is unlikely. The research findings informed the Safety Assessment Federation’s Managing the Risks of Café Boilers (2021) and are informing the approach to inspection within schools of this equipment working in liaison with the Consortium of Local Education Authorities for the Provision of Science Services, CLEAPSS.
This report and the work it describes were funded by the Health and Safety Executive. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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