The HSE's L117 Approved Code of Practice (ACOP) states that there is no specific time period after which you need to provide refresher training or formal assessment. However, you may decide that automatic refresher training or a retest after a set period (for example 3-5 years) is the best way to make sure employees remain competent. Where you adopt this approach, you will still need to monitor performance, in case operators need extra training before the set period ends.