BIZOMAT MAKEOS · Engineering
Noise Exposure Check (Combined Sources, Distance, Dose)
What sound level does the operator get from these machines at their working position, and is their daily noise dose within the limit?
Workplace noise exposure from up to four sources: levels combined by logarithmic addition (as the sound level tool, sum mode), reduced from the reference distance to the operator distance by the inverse-square law (as the distance mode), background noise added, the permitted time at that level from your criterion level, criterion time and exchange rate, the daily dose for the hours exposed and the equivalent eight-hour level.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Source 1 level at the reference distance | dB | Sound level of the first machine measured at the reference distance. |
| Source 2 level (0 = none) | dB | Second machine (0 if not used). |
| Source 3 level (0 = none) | dB | Third machine (0 if not used). |
| Source 4 level (0 = none) | dB | Fourth machine (0 if not used). |
| Reference distance of the source levels | m | Distance at which the source levels were measured. |
| Operator distance from the sources | m | Distance from the sources to the operator’s ear (all sources taken at this distance). |
| Background level at the operator | dB | Background level at the operator from everything else. |
| Hours exposed per day | h | Hours per day the operator spends at this position. |
| Criterion level | dB | Exposure limit level for the criterion time (from your regulation; often 85 dB(A)). |
| Criterion time | h | Time the criterion level may be worn (usually 8 h). |
| Exchange rate | dB | Exchange rate: level change that halves or doubles the permitted time (3 dB in most of the world, 5 dB in some US rules). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Source 1 level at the reference distance
- What it is
- The sound pressure level of the first machine or source, measured at the reference distance with nothing else running, or from the maker’s noise declaration.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 160 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the same frequency weighting for every level as for the criterion level.
What this means: Source 2 level (0 = none)
- What it is
- The level of a second machine measured at the same reference distance as source 1.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 160 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Zero means not used. Levels combine on an energy basis, not by simple addition.
What this means: Source 3 level (0 = none)
- What it is
- The level of a third machine at the same reference distance, if there is one.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 160 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Leave at zero when there is no third source.
What this means: Source 4 level (0 = none)
- What it is
- The level of a fourth machine at the same reference distance, if there is one.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 160 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Leave at zero when there is no fourth source.
What this means: Reference distance of the source levels
- What it is
- The distance from the sources at which their levels were measured or quoted, for example the distance stated in the maker’s noise declaration.
- Units and format
- Enter a number in m: metres. The form accepts 0.1 m to 1000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Operator distance from the sources
- What it is
- The distance from the sources to the operator’s ear position.
- Units and format
- Enter a number in m: metres. The form accepts 0.1 m to 1000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The machine level falls by 20 × log₁₀(r₂ ÷ r₁), about 6 dB for each doubling of distance.
- Get it right
- All sources are treated as one point at this distance; if they are spread out the result is approximate.
What this means: Background level at the operator
- What it is
- The level at the operator from everything else in the area, measured with these machines off. It is added on an energy basis; zero ignores background.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 160 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 70 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hours exposed per day
- What it is
- The time per day the operator spends at this position, exposed to the combined level.
- Units and format
- Enter a number in h: hours. The form accepts 0.1 h to 24 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The daily dose rises in direct proportion.
What this means: Criterion level
- What it is
- The exposure standard level that gives a 100 % dose over the criterion time, as set by the workplace regulation that applies to you.
- Units and format
- Enter a number in dB: decibels. The form accepts 70 dB to 100 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from your regulator; this check does not replace a noise assessment by a competent person.
What this means: Criterion time
- What it is
- The reference duration that goes with the criterion level in your regulation, normally a standard working day.
- Units and format
- Enter a number in h: hours. The form accepts 1 h to 24 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Exchange rate
- What it is
- The exchange rate: the change in level that halves or doubles the permitted exposure time.
- Units and format
- Enter a number in dB: decibels. The form accepts 2 dB to 6 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Set by your regulation; it changes the permitted time a lot for levels far from the criterion.
Method and formulas
- Combined level L = 10 log₁₀ Σ 10^(Lᵢ ÷ 10) (as the sound level tool, sum mode).
- At the operator L₂ = L − 20 log₁₀(r₂ ÷ r₁) (as the distance mode); then add the background logarithmically.
- Permitted time = T_c ÷ 2^[(L − L_c) ÷ ER]; dose = hours ÷ permitted time.
- Equivalent level for the criterion time = L_c + ER × log₂(dose).
- Example: the machines combine to 91.193 dB; at 3 m the operator gets 81.938 dB, a 49.29% daily dose.
Limitations
- Point sources in open space: reflections in a room raise levels above the inverse-square estimate.
- Use A-weighted levels; impulse noise needs a peak check.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether an operator needs hearing protection
- See how far to move a workstation from noisy machines
- Estimate dose for a shift pattern
Who it is for
- Safety officers
- Plant engineers
- Production supervisors
What you get
- Combined level at the sources and at the operator
- Permitted time and daily dose
- Equivalent eight-hour level
Interpreting the result
- Every doubling of distance lowers a point source by about 6 dB, a quarter of the dose at a 3 dB exchange rate.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3455–3456. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Checking, noise and the job record
In Hand Forming Sheet Metal by the Numbers
What it covers: Accept hand-formed parts on thickness, shape and finish, work out a hammering day's noise dose against the exposure standard, catch a noise reading taken in the wrong place, and close the job record.
Method explained here · BIZOMAT original book
Daily exposure and the duty to control
In Machine Noise Control by the Numbers
What it covers: Work out a worker's eight-hour noise exposure and dose, compare it with the exposure standard, apply the hierarchy of control, set a design target, and catch a shift averaged in plain decibels.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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