If the exposure limit value is eceeded, once, or rarely, the risk is not likely. HAVS and CTS take a long time to manifest, there is even an allowance to take into account irregular exposures above the limit in the ACoP. If you are using a points based system, you could inform the employee of the points per hour of each tool and what their maximum allowance would be, so the user knows their limits. If an employee exceeded the limit on one day the emphasis would be on identifying why and to reduce exposure the subsequent day / rest of the week. But you are right that you should be able to minimise this occuring through preiot establishment of exposure limit values / points / useage times. Tool timers (notoriously un-popular) or just employee feedback (a little un-reliable and tends to over estimate actual "trigger" time) can be used to identify actual trigger times. Best bet is to purchase tools with exposures below the limits to start with, but agree this is not always possible

I think that you are correct, you are using the HSE tool after the horse has bolted, and I can see how you can come to this conclusion. How I have used it in the past is to work out how long a person can use the vibrating equipment without going over the exposure levels, i.e. a proactive approach. By inputting the M/s2 value will give you the exposure points and therefore you can work out how long a person can use the tool for before exceeding the limits