Hand-arm vibration cut-off saw: the daily limit

Your gang is halfway along a kerb and somebody already has two numbers on a phone: 3.9 and 13, both in metres per second squared. One is being read off a saw page. The other is a starter figure for masonry cut-off saws. Treated as legal limits, they send the same job in opposite directions.

A hand-arm vibration cut-off saw assessment is a daily dose, written A(8). The Control of Vibration at Work Regulations 2005 set the exposure action value at 2.5 m/s² A(8) and the exposure limit value at 5 m/s² A(8). Those are eight-hour figures for the person holding the tool. The 350 mm diamond blade listings we used do not state a vibration magnitude, and this page will not invent one.

In short

The legal thresholds are daily exposures, summed across the tools that person actually ran. Use the machine's own magnitude when you have one, and the Health and Safety Executive's 13 m/s² only as the initial value for a masonry cut-off saw when you do not. A worn disc has no vibration number in our listings, and the extra trigger time is what pushes the day over the action value.

Action value and limit value

Regulation 4 sets the two hand-arm thresholds: 2.5 m/s² A(8) at the action value and 5 m/s² A(8) at the limit value. The Health and Safety Executive states the same pair. Both describe a working day normalised to eight hours, so a saw quoted at 6 m/s² has not on its own broken the limit, and a saw quoted at 2 m/s² has not on its own stayed under the action value. You still attach the minutes the trigger was held.

Schedule 1 builds the sum. Daily exposure equals the vibration magnitude multiplied by the square root of trigger time divided by eight hours. Jobs with different magnitudes are combined, and the greater of the two hands is the one that counts.

At or above the action value you reduce exposure so far as is reasonably practicable, and information, training, and health surveillance come with that duty. The limit is a ceiling for a single day. If it is exceeded, bring exposure down the same day and find out why. Employers and self-employed cutters are both in scope. In Northern Ireland, use the Northern Ireland vibration regulations. The daily hand-arm figures are still 2.5 and 5 m/s² A(8).

Do not borrow the wrong vibration number

The Health and Safety Executive's table puts masonry cut-off saws in a range of 5 to 14 m/s² and recommends 13 m/s² when you have nothing better. That 13 is a class assumption, not a named model and not the blade. Drop it once you hold the manufacturer's figure, or a competent measurement of the saw you own.

The Stihl UK page for the TS 420 describes the vibration as extremely low and, on the page we used, does not give a magnitude for Schedule 1. Seddon prints 3.9 m/s² and 98 dB(A) for that saw. The 3.9 is vibration for the machine. The 98 dB(A) is noise. Neither belongs to a blade, and neither is the Health and Safety Executive's 13.

Eight hours at a constant 3.9 m/s² is a daily exposure of 3.9 m/s² A(8): over the action value and under the limit. The times that follow are Schedule 1 applied to those published magnitudes, not a test we ran. On 13 m/s² the action value is about 18 minutes of trigger time and the limit about 1 hour 11 minutes. On 3.9 m/s² the action value is about 3 hours 17 minutes and the limit about 13 hours.

How long the trigger can stay down

Count the time the saw is running in the hands, not the hours it sat on the van. Twenty minutes of cutting inside a four-hour kerb job is twenty minutes, plus every other vibrating tool that person used.

The dose rises with the square of the magnitude. Use 13 m/s² when you lack data, label it as the initial value, and write the source next to the number.

Assess each person who shares the saw. One hundred exposure points match the action value and four hundred match the limit, so a breaker and the cutter add. An initial 13 overstates a lower-vibration saw and can understate a neglected one. If the machine chatters or the guard is loose, reassess before you extend the trigger time.

Why a blunt blade matters

HSE leaflet INDG461 makes the practical link. Worn discs increase cutting time, and cutting time is exposure. A diamond blade in the listings we compared has no hand-arm vibration magnitude. A glazed rim, a reduced diameter, or missing segments change how long you stand on the same kerb. That extra minute is a vibration minute.

Check diameter, bore, and the materials a listing names before you leave a disc on the saw. Those amazon.co.uk listings do not give a figure in m/s². A disc that still cuts can shorten trigger time. It does not replace the daily sum.

Forcing a glazed rim, or a disc that does not match the guard, adds minutes and a kick risk. The saw-fit guide covers bore and guard before the saw starts. The how-to-use guide covers the cut. Neither page is a vibration certificate for the blade.

This is not a blade ranking

The figures in this article come from the 2005 regulations on legislation.gov.uk, the Health and Safety Executive's regulations and risk-assessment pages, the Stihl UK page for the TS 420, and Seddon's printed 3.9 m/s² and 98 dB(A) for that saw. We did not run a laboratory test and did not fit a meter to a cut-off saw. Blade details come from amazon.co.uk listings. A qualifying purchase through those links can earn us a commission at no extra cost to you.

The top pick in the comparison is the PRODIAMANT 350 mm, 20 mm bore, at a captured price of £54.78. The listing states a 15 mm turbo segment, a 3.5 mm thickness, wet or dry cutting, and EN 13236. It names concrete, reinforced concrete, granite, kerbs, brick, and masonry, and it names no vibration magnitude. One UK complaint said it did not fit a Stihl saw without a washer that was not supplied. Asphalt is not named.

That comparison cannot show which blade vibrates less. The buying guide stays on fit and material. Treat a claim that a rim halves vibration as advertising unless the saw manufacturer measured that disc on that model and published the magnitude.

What an employer does at the action value

Start from the saw on the job. You want the manufacturer's magnitude for that model, on the handle the operator holds. "Low vibration" is not a number. Until you have one, use 13 m/s² for a masonry cut-off saw and write "initial value" beside it, so 13 is never later filed as a TS 420 result. Log each cutter's trigger time.

When the action value is likely, rotate the cutting, keep a disc that still cuts, and maintain the saw so the figure still describes it. Tell the gang the magnitude, the minutes that go with it, and the symptoms to report the same day: tingling, numbness, loss of grip, or fingers that go white in the cold. Those signs sit with hand-arm vibration syndrome, including vibration white finger. Take that person off the saw.

Health surveillance belongs where exposure is likely to reach the action value, or where someone already has a diagnosis. If the sum reaches the limit value, change the job that day. Splitting the minutes across two operators changes the dose. A second saw does not, if the same person still holds the trigger.