I have an employee with a weak ankle due to old football injuries who, during his normal work stepped from plant using the steps provided and when he put his weight on his pre injured ankle, the ankle gave way resulting in a sprain. The employee did not slip, had three points of contact, was wearing safety boots with ankle support and was carrying out an action that he and others carry out each day without problem. Do i need to report this under RIDDOR? The height of the step was 18 inches, the plant is CE approved and the steps were used as intended.

I dont agree with jwk. Well assuming hat the "sprain" resulted in enough lost time for it to be a riddor. Then surely it is a RIDDOR. The accident was that someone sprained their ankle stepping down from a piece of plant. THe test is not whether it was caused by work but whether it was "arriving out of or in connection with work" stepping down from the plant very obviously was "out of or in connection". Its also not about whether you think that you've done all that is reasonable to stop an accident happening. The fact is that an accident has happened. RIDDOR is triggered by degree of harm not the cause. The fact that your colleague had a pre-existing weakness is irrelevant to whether its a RIDDOR. It is of course entirely relevant to the conclusions you draw from the investigation. Think of an analogy. Your colleague had a severe reaction to a chemical at use at work which resulted in a week off sick. For the purposes of RIDDOR its irrelevant that the person was medically different from his colleagues. Are you really intending to quiz any member of staff about their medical history before you decide whether an incident is a RIDDOR or not?

I would say no, because if the ankle gave way due to a pre-existing injury and not due to work process (dodgy step, slippery floor etc) then there was no accident IMO. I recently had a driver pop his knee while climbing into a lorry cab due to a pre-existing injury. Goes in the first aid book and that's it. The injury was not caused by work or by a work process and what would you do to stop it from happening again? Where would this sit in a Risk Assessment? etc would be by reasons for not reporting.