Health and safety legislation doesn’t generally apply to someone who is not an employer, self-employed or an employee.
The Health and Safety at Work etc Act 1974 (HSW Act) and the regulations made under it apply if any organisation (including a voluntary organisation) has at least one employee.
The HSW Act sets out the general duties that employers have towards employees. It also requires employers and the self-employed to protect people other than those at work (eg members of the public, volunteers, clients and customers) from risks to their health and safety arising out of, or in connection with, their work activities.
You can find more information at the Voluntary organisations site.