Scope. These calculations help organise daily exposure information. They do not replace a risk assessment, representative measurement, health surveillance decision, hearing-protection assessment or a competent occupational-hygiene review.
Two exposures, two different calculations
Hand-arm vibration is built from acceleration magnitude in metres per second squared (m/s²) and trigger time. Daily noise exposure uses A-weighted equivalent continuous sound level, written LAeq,T, and the duration represented by that level. The two results use different units and cannot be merged into one score.
Both methods depend more on representative inputs than on calculator precision. A catalogue vibration value may not describe the accessory, material, maintenance and grip used on the job. A spot noise reading may miss changing operations, distance, reflections or impulsive events. Record the source and context of every input.
Build the record around one person and one exposure day. Do not combine different workers because they share a tool, and do not divide a task total by the crew unless trigger time was actually shared that way. A planned rota needs observed or defensible individual periods.
Hand-arm vibration: magnitude and trigger time
Trigger time means the period during which the person’s hands are actually exposed to vibration, not the full shift, hire period or time the tool is switched on nearby. HSE tells employers to estimate or measure exposure and use realistic time information. [HSE]
For each exposure, Job Lab points are P = 2a²T, where a is vibration magnitude in m/s² and T is trigger time in hours. Combined daily exposure is A(8) = √(Σ(aᵢ²Tᵢ) ÷ 8). [LAW] Use one row for each materially different tool, accessory or operating condition.
Do not reduce exposure time to the planned cut count without checking actual trigger behaviour. Include repeated short operations, clearing and finishing passes where the hands remain exposed. Conversely, do not count breaks, setup or unpowered handling as trigger time.
Vibration action and limit values
The Control of Vibration at Work Regulations 2005 sets a daily exposure action value (EAV) of 2.5 m/s² A(8) and a daily exposure limit value (ELV) of 5 m/s² A(8). In the HSE points system these correspond to 100 and 400 points. The Regulations came into force on 6 July 2005. [LAW] [HSE]
At or above the action value, the legal/control response matters; 400 points is not a daily budget that grants permission to continue. Exposure must not exceed the limit value, and control duties are not postponed until a threshold is crossed. The calculator labels a numerical position only.
Where values vary, avoid choosing the quietest or smoothest number. Record the range and the basis used for assessment. HSE guidance covers reducing exposure, information/training and health surveillance; the calculation alone does not decide those actions. [HSE]
Magnitude can change with worn consumables, imbalance, feed force, material and tool condition. When manufacturer data covers several modes, use the value that matches the actual setup and include declared uncertainty where the assessment method requires it. If the setup falls outside the data, measure or obtain better evidence rather than borrowing a nearby model’s number.
Daily noise: level, duration and energy
Decibels are logarithmic, so 88 dB(A) and 94 dB(A) must not be averaged as 91. The daily personal noise exposure formula is LEX,8h = 10 log10((Σ tᵢ × 10^(Lᵢ/10)) ÷ 8), where each Lᵢ is a representative LAeq,T level and tᵢ is its non-overlapping duration in hours. [LAW]
Build the day as exposure periods: drilling, cutting, clearing, travel in a noisy cab, or other materially different conditions. A period may represent repeated events only if its level and duration are genuinely representative. Overlapping rows double-count energy and must stop the result.
Extended-duration noise is not assessed by looking only at the loudest tool. A lower level sustained for much longer can contribute substantial daily energy. Conversely, a short high-level event can dominate. HSE’s calculator and ready-reckoner use the energy relationship to combine periods. [HSE]
Noise action and limit values
The lower exposure action value is 80 dB(A) daily or weekly personal exposure; the upper action value is 85 dB(A). The exposure limit value is 87 dB(A), taking account of hearing protection worn by the worker. Peak sound pressure has separate C-weighted action and limit values and is not calculated by this daily LAeq route. [LAW] [HSE]
An unadjusted 87 dB(A) calculator result is therefore not, by itself, a valid comparison with the limit-value treatment. The tool does not subtract a hearing protector’s labelled attenuation. Real protection depends on selection, fit, wear time and the workplace; excessive attenuation can introduce communication or warning-signal problems.
Where daily exposure varies markedly, the Regulations permit weekly exposure in specified circumstances, but that is not an automatic averaging option. A competent assessment must establish whether weekly treatment applies and ensure risks are appropriately controlled. [LAW]
Peak sound is a separate reason to escalate. Cartridge tools, impacts, bursting processes and similar events may require peak measurement even where a daily energy estimate looks modest. The daily tool deliberately has no field that pretends LAeq can stand in for peak C-weighted pressure.
Worked records
Hand-arm vibration
Exposure A is 5 m/s² for 2 hours: 2 × 5² × 2 = 100 points. Exposure B is 10 m/s² for 0.5 hour: 2 × 10² × .5 = 100 points. Total: 200 points. Combined A(8) = √((25×2 + 100×.5)÷8) = 3.536 m/s². The display is above the action value and below the limit value; it is not an instruction to continue.
Daily noise
A representative period of 88 dB(A) lasts 2 hours and a 94 dB(A) period lasts 0.5 hour. Energy combination gives LEX,8h = 84.98 dB(A). An arithmetic mean would be technically wrong. The record still needs source/context for each level and confirmation that periods do not overlap.
Controls come before calculator reassurance
Reduce exposure at source where reasonably practicable: consider the work method, lower-exposure equipment for the actual task, maintenance, consumables, support/jigs, job rotation where it genuinely reduces individual exposure, and scheduling. HSE’s vibration guidance emphasises eliminating or reducing vibration exposure rather than relying on a calculation. [HSE]
For noise, first consider eliminating or reducing the noisy process, enclosure, isolation, distance, maintenance and time. Hearing protection is part of a control programme where required, not a substitute for reasonably practicable engineering and organisational controls. HSE explains duties at the action values and the role of hearing protection zones. [HSE]
Do not select hearing protection from this page. A protector assessment needs the noise spectrum or an appropriate selection method, compatibility with other personal protective equipment, audibility needs, fit and wear. Likewise, gloves do not create a generic correction to the vibration magnitude.
Practical records should identify the control owner and review trigger. A changed blade, new substrate, longer shift, enclosed room, failed extraction or altered sequence can invalidate yesterday’s inputs. Set a review point before work, not only after a value has been exceeded.
For vibration, symptoms such as tingling, numbness or loss of dexterity are not calculator variables. They require the organisation’s health-reporting and occupational-health route. For noise, difficulty communicating or ringing in the ears should not be normalised as evidence that the arithmetic was conservative.
Use equipment information as a starting point, not a permanent job value. Note the tool model, accessory, material, operating mode, maintenance condition and source date. If workplace measurement is undertaken, the record needs instrument identity, calibration status, measurement position, sampling period and the competent interpretation applied. These details explain why a value represents the job and make later review possible.
Duration deserves the same discipline. Observe several cycles, distinguish trigger-on work from handling, and include other exposures during the shift. For noise, map the person’s movement between areas; a fixed meter beside the machine may not represent the wearer. For vibration, shared equipment does not imply equal exposure. A short survey should state what uncertainty remains rather than hiding it behind a three-decimal A(8) display.
Dust controls can change tool handling, trigger time and noise. Where extraction or water suppression is involved, record the combined method and read Controlling dust at the source.
When the result must be withheld or escalated
Do not show the affected exposure result when:
- vibration magnitude or actual trigger time is missing or not tied to the task;
- noise rows overlap, or a level is not representative of its period;
- peak or impulsive noise is material but only daily LAeq data has been entered;
- the day varies materially and a weekly assessment question arises;
- hearing-protection effects are being used without a proper assessment;
- symptoms, unusual operating conditions or a changed process require review.
Keep the source of each input, dates, work method and controls with the record. See the HAVS source group, noise source group and Methodology for versioning and rounding.
This guide explains exposure arithmetic and planning records. It does not confirm that a work method or exposure is safe or compliant, and it does not replace the assessment and control duties in the Regulations.