Short answer
Anyone carrying out work on gas fittings in commercial premises in Great Britain must be on the Gas Safe Register, and they may only do the types of work listed on their registration. Commercial work is recorded separately from domestic, so an engineer needs specific non-domestic categories for the appliances and pipework they work on.
Why registration is a legal requirement
The Gas Safety (Installation and Use) Regulations 1998 require that anyone working on gas fittings is competent and that the business they work for is a member of the class of persons approved by HSE — currently the Gas Safe Register. Using an unregistered or unqualified engineer leaves the duty holder exposed if something goes wrong.
Domestic vs commercial
Registration lists each competence separately. Commercial categories cover larger pipework, higher pressures and non-domestic appliances such as catering equipment, overhead heaters and plant room boilers. A domestic-only engineer cannot legally carry out this work, even on a small installation in a shop or office.
How competence is gained
Engineers prove competence through the Nationally Accredited Certification Scheme (ACS) or an equivalent route, assessed at an approved centre and renewed every five years. Their Gas Safe ID card then shows the categories they hold.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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