Noise Exposure Dose and Daily Exposure Level Calculator
Noise Exposure Dose and Daily Exposure Level Calculator
Daily noise dose, permitted duration and the equivalent eight-hour level, with the exchange rate as an input — because a 3 dB and a 5 dB rate give permitted times that differ several-fold for the same measured level.
Noise exposure dose
3 dB and 5 dB exchange rates95 dB(A) for 3 hours, against a 90 dB(A) criterion with a 5 dB exchange rate
Formula
- L
- the A-weighted sound level in dB(A) for the period
- C
- the hours spent at that level
- Lc, the criterion level
- the level that is a 100% dose over eight hours. 90 dB(A) is OSHA’s permissible exposure limit; 85 dB(A) is the NIOSH recommended exposure limit and the EU and UK upper exposure action value. OSHA separately defines “an 8-hour time-weighted average of 85 decibels or a dose of fifty percent” as its action level
- q, the exchange rate
- the decibels that halve the permitted time. 3 dB is the equal-energy rule of ISO 1999, used by the EU directive and recommended by NIOSH; 5 dB is used by OSHA and some other US schemes. At L = Lc both give eight hours; above it the 5 dB rule is the more permissive and the gap grows
- the OSHA form
- 29 CFR 1910.95 Appendix A writes the same relation as T = 8/2^((L−90)/5), the dose as D = 100(C1/T1 + C2/T2 + … + Cn/Tn) for a shift of several levels, and the conversion back to an equivalent average as TWA = 16.61 log10(D/100) + 90. That 16.61 is 5 ÷ log10 2, which is why the general form above reproduces it exactly
- the equal-energy form
- with q = 3 the general eight-hour equivalent reduces to L + 10 log10(C/8) to within the rounding of 3 ÷ log10 2 = 9.97 to 10, which is the familiar L(EX,8h) of ISO 1999 and of the EU directive
- a shift of several levels
- add the doses. Each period contributes 100 × C ÷ T with its own level, and the day’s dose is the sum. OSHA’s Table G-16 footnote states the same thing as a sum of fractions C1/T1 + C2/T2 + … exceeding unity
- what this does not do
- render a compliance verdict. It computes the physics of the exposure. Whether an exposure meets or exceeds a legal limit depends on the jurisdiction, the measurement method, whether hearing protection may be counted, and the peak sound pressure, which is a separate C-weighted instantaneous limit and is not derivable from an A-weighted average
Worked example
95 dB(A) for 3 hours, against a 90 dB(A) criterion with a 5 dB exchange rate
T = 8 ÷ 2^((95 − 90) ÷ 5) = 8 ÷ 2^1 = 4.00 hours permitted at 95 dB(A), which the result card shows as 240.0 minutes. That is OSHA's Table G-16 row for 95 dB(A), re-derived rather than looked up
Dose = 100 × 3 ÷ 4.00 = 75.0%
Eight-hour equivalent = 95 + (5 ÷ log10 2) × log10(3 ÷ 8) = 95 − 7.07 = 87.9 dB(A). OSHA's own Appendix A formula, TWA = 16.61 × log10(75/100) + 90, gives the same 87.9
Now change only the exchange rate. At 3 dB, T = 8 ÷ 2^(5 ÷ 3) = 2.52 hours and the same 3 hours becomes a 119.1% dose. One input changed, and the dose moved by more than half again
They coincide at the criterion level and nowhere else. At 90 dB(A) both rates give exactly 8.00 hours. That is the only level at which the choice does not matter, and a calculator tested only there would pass with either rate wired in
Three levels above it. At 95 dB(A): 4.00 hours against 2.52, a ratio of 1.59. At 105 dB(A): 1.00 hour against 0.25, a ratio of 4. At 115 dB(A): 0.25 hours against 0.02, a ratio of 10.1. The divergence is not a constant — it grows with level, because the two rules are different exponentials
And below the criterion the order reverses. At 80 dB(A) the 5 dB rule permits 32 hours and the 3 dB rule 80 h 38 min — so the 3 dB rule is not simply the stricter of the two, it is the steeper
The two real schemes, which differ in criterion as well as rate. At 95 dB(A), OSHA's 90 dB criterion with a 5 dB rate permits 4.00 hours; NIOSH's 85 dB criterion with a 3 dB rate permits 0.79 hours, which is 48 minutes. Five times the permitted time for the same measured level
OSHA's action level, checked. Eight hours at 85 dB(A) against a 90 dB(A) criterion with a 5 dB rate gives T = 16.00 hours and a dose of 50.0%, which is exactly how OSHA defines its action level
Permitted daily duration at each level, under the two exchange rates
| Level dB(A) | 5 dB rate, 90 dB criterion | 3 dB rate, 90 dB criterion | Ratio | 3 dB rate, 85 dB criterion (NIOSH) |
|---|---|---|---|---|
| 80 | 32 h | 80 h 38 min | 0.40 | 25 h 24 min |
| 85 | 16 h | 25 h 24 min | 0.63 | 8 h |
| 90 | 8 h | 8 h | 1.00 | 2 h 31 min |
| 95 | 4 h | 2 h 31 min | 1.59 | 47 min 37 s |
| 100 | 2 h | 47 min 37 s | 2.52 | 15 min |
| 105 | 1 h | 15 min | 4.00 | 4 min 43 s |
| 110 | 30 min | 4 min 43 s | 6.35 | 1 min 29 s |
| 115 | 15 min | 1 min 29 s | 10.08 | 28 s |
Action values and limit values, by scheme
| Scheme | Action value | Limit | Exchange rate | Peak |
|---|---|---|---|---|
| OSHA, 29 CFR 1910.95 | Action level: 85 dB(A) 8-hour TWA, a 50% dose | Permissible exposure limit: 90 dB(A) 8-hour TWA | 5 dB | Impulsive or impact noise not to exceed 140 dB peak |
| NIOSH | — | Recommended exposure limit: 85 dB(A) over 8 hours | 3 dB | — |
| EU Directive 2003/10/EC | Lower 80 dB(A), peak 112 Pa; upper 85 dB(A), peak 140 Pa | Exposure limit value 87 dB(A), peak 200 Pa | 3 dB (ISO 1999 equal energy) | 112 / 140 / 200 Pa, C-weighted |
| UK Control of Noise at Work Regulations 2005 | Lower 80 dB, peak 135 dB; upper 85 dB, peak 137 dB | 87 dB daily or weekly exposure, peak 140 dB | 3 dB | 135 / 137 / 140 dB LCpeak |
Two exchange rates, and why the choice matters more than the level
Noise exposure arithmetic is a trade between level and time, and the rate of that trade is a policy choice rather than a physical constant. The equal-energy rule says that doubling the acoustic energy halves the tolerable duration, which is a 3 dB exchange rate: it is what ISO 1999 defines, what the EU directive and the UK regulations use, and what NIOSH recommends. OSHA and some other US schemes use a 5 dB rate, which permits substantially longer exposures at high levels. Both are in force, in different places, for the same ears.
The size of the difference surprises people. The two rates agree exactly at the criterion level — eight hours, by definition, whichever rule you use — and separate from there by a factor that grows with level. Against a 90 dB(A) criterion, 95 dB(A) buys four hours under the 5 dB rule and two and a half under the 3 dB rule; 105 dB(A) buys an hour against fifteen minutes; 115 dB(A) buys a quarter of an hour against a minute and a half. Compare the two real schemes rather than the two rates in isolation and the gap is wider still, because they differ in criterion level too: at 95 dB(A), OSHA’s limit permits four hours and NIOSH’s recommendation permits forty-eight minutes. One measurement, a fivefold difference in the answer.
Below the criterion level the ordering reverses, which is the half of the comparison usually left out. At 80 dB(A) against a 90 dB(A) criterion the 5 dB rule permits 32 hours and the 3 dB rule 80 and a half. The 3 dB rule is not uniformly the stricter one; it is the steeper one, more generous at low levels and far less generous at high ones. That is exactly what an equal-energy rule should do.
Two things this page deliberately will not do. It will not render a compliance verdict: it computes a dose, a permitted duration and an eight-hour equivalent level, and whether any legal threshold is met depends on the jurisdiction, on how the exposure was measured, and on whether hearing protection may be counted — the EU directive allows protector attenuation to be set against the exposure limit value and expressly forbids it against the action values. And it will not compute peak sound pressure, which is a separate limit on a C-weighted instantaneous measurement and cannot be derived from an A-weighted average at all. Audiometric results are equipment- and calibration-dependent: the dB HL scale is defined against the reference equivalent threshold levels of the ISO 389 series for a particular transducer and coupler, so the same ear can read differently on two audiometers, and the BSA recommended procedure puts the uncertainty of any threshold measurement at no better than plus or minus 5 dB. Your own audiogram and the calibration standard it was recorded against govern, not this arithmetic. This page computes the number and names the body that publishes the thresholds. It does not decide anything: the grades, action values and criteria quoted here are scheme- and jurisdiction-specific, and whether any of them is met in a particular case, and what should follow, is for the clinician, the audiologist or the responsible person under the applicable regulation to determine.
Frequently asked questions
How do you calculate a daily noise dose?
Find the permitted duration T at the measured level, T = 8 ÷ 2^((L − criterion) ÷ exchange rate) hours, then the dose is 100 × hours ÷ T. Three hours at 95 dB(A) against a 90 dB(A) criterion with a 5 dB rate gives T = 4 hours and a 75% dose. For a shift at several levels, add the periods’ doses.
What is the difference between a 3 dB and a 5 dB exchange rate?
How many decibels halve the permitted time. They agree at the criterion level and diverge above it: at 95 dB(A) against a 90 dB(A) criterion the 5 dB rule permits 4 hours and the 3 dB rule 2 hours 31 minutes; at 105 dB(A) it is an hour against fifteen minutes. Below the criterion level the 3 dB rule is the more generous of the two.
Which exchange rate should I use?
The one the applicable regulation specifies. OSHA uses 5 dB with a 90 dB(A) permissible exposure limit; NIOSH recommends 3 dB with an 85 dB(A) limit; the EU directive and the UK regulations use the ISO 1999 equal-energy 3 dB rule with 85 dB(A) as the upper action value and 87 dB(A) as the limit value.
What are the noise action values?
Under Directive 2003/10/EC and the UK Control of Noise at Work Regulations 2005, a lower action value of 80 dB(A) daily exposure with a peak of 112 Pa (135 dB) and an upper action value of 85 dB(A) with 140 Pa (137 dB), with an exposure limit value of 87 dB(A) and 200 Pa (140 dB). OSHA instead has an action level of an 85 dB(A) eight-hour average, which it defines as a 50% dose.
Does hearing protection count towards the exposure?
It depends which figure. The EU directive states that the exposure limit values “shall take account of the attenuation provided by the individual hearing protectors worn by the worker” and that “the exposure action values shall not take account of the effect of any such protectors”. Enter the unprotected exposure here.
Related calculators
References
- Occupational Safety and Health Administration. 29 CFR 1910.95 — Occupational noise exposure, and Appendix A, Noise exposure computation. Washington, DC: US Department of Labor.
- Directive 2003/10/EC of the European Parliament and of the Council of 6 February 2003 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise), Articles 2 and 3.
- National Institute for Occupational Safety and Health. Understand noise exposure. Atlanta, GA: CDC/NIOSH.
- Health and Safety Executive. Noise at work: a brief guide to controlling the risks, INDG362. Bootle: HSE.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/