Trigger time is the whole assessment
Everything else on this page is arithmetic. The one judgement is how long the tool was actually running in somebody's hand, and it is nearly always wrong.
Ask anybody how long they used the breaker and they will tell you about the task. Four hours. Time it with a stopwatch and it is ninety minutes, because the rest was setting up, moving, clearing spoil, changing the point, waiting for the dumper and standing about.
That is not a small correction. Exposure goes with time directly, so a trigger time that is three times too high produces a number three times too high, and an assessment built on it is a document rather than an assessment.
The two numbers from regulation 4
For hand-arm vibration the exposure action value is 2.5 m/s² A(8) and the exposure limit value is 5 m/s² A(8). For whole-body it is 0.5 and 1.15.
They do different jobs. The action value brings in duties: a programme of control measures, and health surveillance. The limit value is a ceiling that exposure must not exceed.
Health surveillance sits at the action value, under regulation 7(1). That catches people out, because the instinct is that the serious duties arrive at the serious number.
Points exist because decibels of vibration do not add
A(8) is a magnitude scaled by the square root of time. Square roots do not add, so you cannot total two tools by totalling their A(8) values.
Two tools at A(8) 3.0 each is not 6.0. It is the root of the sum of the squares, 4.24. Adding them straight overstates the exposure by 40%, and it is exactly what somebody with a clipboard and no calculator will do.
Points fix that by squaring first. Points are 16 × A(8)², which puts the action value on exactly 100 and the limit on exactly 400, and points add up like normal numbers. It is not a different rule, it is the same rule in a form you can do in your head.
Anti-vibration gloves are not a control
This one is worth being blunt about because it gets written into risk assessments as a control measure and it is not one.
Gloves marketed as anti-vibration do very little at the frequencies that cause hand-arm vibration syndrome. Worse, a gloved hand has less grip, so people hold the tool tighter, and grip force is itself part of what does the damage.
What genuinely helps is keeping hands warm and dry, because cold cuts circulation and circulation is what the condition attacks. So wear the gloves for warmth. Just do not write them down as control and do not expect them to change a number.
The magnitude is softer than it looks
The figure in the manual comes from a standardised test under standardised conditions. Real use is frequently worse.
A blunt disc, a worn tool, a harder material, a different operator or a bad technique all push it up, sometimes a long way. HSE's position is that declared values often understate what a tool does in service, so treat the manual as a starting point rather than as the answer.
The starter figures on this page are representative, not measured, and they are there so somebody with nothing can begin. They are not your tool.
HAVS does not get better
The damage is to nerves and blood vessels in the hand and it is permanent. Vibration white finger, numbness, loss of grip, loss of dexterity, and an inability to work in the cold that ends careers in outdoor trades.
It also accumulates over a working life rather than over a day, so the regulations care about the average and why health surveillance exists. Somebody who is fine now and was over the action value for fifteen years is not fine.
Common questions
What counts as trigger time?
The time the tool is actually running in the hand. Not the length of the task, not the time on site, not the shift. A breaker somebody says they used all day is usually about two hours of trigger time once you time it, because of setting up, moving, clearing, waiting and everything else. It is the input that decides the answer and it is almost always overstated.
What are the exposure action and limit values?
Regulation 4 of the Control of Vibration at Work Regulations 2005 sets them. Hand-arm: an exposure action value of 2.5 m/s² A(8) and an exposure limit value of 5 m/s² A(8). Whole-body: 0.5 and 1.15 m/s² A(8). The action value brings in duties. The limit value must not be exceeded at all.
When does health surveillance kick in?
At the action value, not the limit. Regulation 7(1) triggers it where the risk assessment shows a health risk, or where employees are likely to be exposed at or above an exposure action value. People routinely assume it starts at the limit, which is the point at which the exposure should not be happening in the first place.
What are exposure points and why not just use A(8)?
Because A(8) values do not add up and points do. Points are just A(8) squared and rescaled so the action value lands on 100 and the limit on 400. Two tools at A(8) 3.0 each is not 6.0, it is the root of the sum of the squares, 4.24. In points it is 144 plus 144. Same arithmetic, no square roots needed on site, which is why HSE published a ready reckoner in points.
Do anti-vibration gloves reduce my exposure?
No, and they are not a control measure. They do very little at the frequencies that cause the damage, and because a gloved hand has to grip harder to keep hold of a tool they can make exposure worse. Keeping hands warm and dry genuinely does help, because cold reduces circulation and circulation is what HAVS attacks, so gloves are worth wearing for that reason. No glove changes the number this calculator produces.
Can I use the vibration figure from the manual?
As a starting point. The declared value comes from a standardised test, and HSE's position is that real use is often worse: a blunt disc, a worn tool, a harder material or a different technique all push it up. Where the figure actually matters, get data for your tool in your use rather than for the model in a laboratory.
Is being under the limit value good enough?
No. The limit is a ceiling, not a target. Regulation 6 requires exposure to be reduced to as low as reasonably practicable whatever the number is, so a day that comes out at 4.9 m/s² is legal and is still a day that should be looked at. HAVS is permanent and it is cumulative across a working life.