What happens after the training
Ebbinghaus described it in the nineteenth century and it has been confirmed repeatedly since: knowledge that goes unused drains away fast. The steepest part of that curve is in the first few days.
For a training day that means something uncomfortable. The assessment at the end measures a peak that is no longer there two weeks later. The organisation has a certificate, the employee has a memory, and the knowledge it was all about has largely gone.
In industry that stings more, because it often concerns the rare operations, precisely the things you do not practise daily and which therefore drain away hardest.
Why retrieval works, and rereading does not
There is an important difference between two kinds of repetition, and that difference decides the return.
Reading the material again feels effective. It goes smoothly, it seems familiar, and that feeling of familiarity gets mistaken for knowledge. Research consistently shows the effect is limited.
Active retrieval, putting the question to yourself without the answer in front of you, feels harder and works considerably better. Every time you pull something out of memory, the trace gets stronger. The effort is the mechanism, not a side effect.
That is why a short assessment question three weeks after the training delivers more than sending round the slide deck again.
The rhythm to hold to
The main line is: close together first, further apart afterwards.
A workable schedule for a safety subject is a repetition after two or three days, then after two weeks, then after six weeks, then after half a year. Four moments of five minutes spread over time, against one session of a day.
More important than the exact intervals is that there are intervals at all. Anyone who does not follow the schedule perfectly but does spread it out captures most of the gain.
In practice
Three things make the difference between a schedule on paper and repetition that actually happens.
Automate it. Repetition somebody has to schedule by hand happens in the first month and not after that. A system that sends a question itself keeps running.
Keep it short and without consequences. Five minutes, no record going to the supervisor. The moment a score is tracked that somebody gets held to, behaviour changes and the learning value disappears.
Repeat the failure modes, not the material. Not the whole procedure again, but the three points where it goes wrong in practice. That is where the gain sits, and it is a fraction of the content.
The outcome is measurable: the same training, the same people, but a considerably higher share of the knowledge still present six months later. Without a single extra training day.
Spaced repetition works best as a fixed part of your programme rather than as a separate action. Where it fits into the whole is in the guide on setting up or renewing a corporate academy. The term itself is explained briefly under spaced repetition.