How long a tool can be used before the day is spent VIBRATION

Double the tool, quarter the time

Hand-arm vibration exposure is short arithmetic and completely unforgiving, because exposure goes with the square of the magnitude:

A(8) = √( Σ a² × T / 8 )

Which produces the one fact everybody should carry: double the magnitude and you quarter the time. A tool at 10 m/s² reaches the exposure action value in half an hour and the exposure limit in two.

And this is exactly where the intuition fails. Handed a tool twice as rough as the last one, people assume they have half the time. They have a quarter. That single misjudgement is how somebody who believes they are working within the limits spends years over them, and hand-arm vibration syndrome is permanent: the damage does not recover when the exposure stops.

Why it works in points as well

Because points add and A(8) figures do not. You cannot average two A(8) values, and you cannot add them, which makes a day spent on three different tools genuinely awkward to reason about in the published units.

Exposure points are the same arithmetic rearranged so that the day's total is a sum: each tool for each duration gives a number of points, the points add up, and the action value and limit are fixed point totals. That is a calculation somebody can do on a job sheet at seven in the morning, which is the only version of it that gets done.

The magnitude you use is the number that decides everything

Since exposure goes with the square, the figure you put in matters more than anything else on the page, and the manufacturer's declared value is the wrong one to use. It is measured under standardised conditions with a new tool, a sharp bit and a test material, and in-use values are routinely two or three times higher. Squared, that is a four- to nine-fold difference in exposure.

Use measured in-use data for the tool as it is, on the material it is used on, with the accessory it is used with. Published in-use databases for common tools exist and are far closer than the declaration. Blunt consumables are a large part of the difference, which makes changing the disc a vibration control and not just a productivity one.

And use trigger time, not shift time. The number that counts is how long the tool was actually running in the hand, which is usually a small fraction of the time somebody was holding it, but it is a fraction that has to be estimated honestly rather than optimistically.

The real point of the arithmetic is that it is a design tool. If the day does not fit, the answer is a different tool, a different method, a second person to share the task, or removing the need for it, not a note in a file. Nothing you type is uploaded; it stays in this browser. Nearby: NOISE does the same for hearing, WEL for substances in the air, and HEAT for working in it.