The HSE guidelines given in their Approved Code of Practice suggest the following cover (this is a rough guide rather than a rule and more details can found in the HSE ACOP):
For Low Hazard Environments:
- Less than 25 employees - At least one Appointed Person
- 25 to 50 employees – At least one First Aider Trained in Emergency First Aid
- More than 50 employees – At least one trained First Aider for every 100 employees
For High Hazard Environments:
- Less than 5 employees - At least one Appointed Person
- 5 to 50 employees – At least one First Aider Trained in Emergency First Aid or a Qualified First Aid at work first aider based on an assessment of the type of injuries that might be occur in the workplace
- More than 50 employees – At least one trained First Aid at work first aider for every 50 employees