LEX,8h — noise exposure

LEX,8h is a worker’s daily personal noise exposure level: the equivalent level that, if held constant for an 8-hour reference shift, would contain the same sound energy as the worker’s real exposure over the day. It is the principal energetic index on which Italian D.Lgs 81/08 — the Consolidated Workplace Safety Act — builds its action values and its limit value. It is not, however, the whole noise risk assessment: art. 190 requires impulsive noise, particularly sensitive workers, interactions with ototoxic substances and vibration, interference with warning signals, exposure beyond normal working hours, the availability of PPE and the existence of quieter alternatives all to be considered. This Open Lab tool computes LEX,8h from one or more exposure periods and says which band it falls in with respect to the action and limit values, with the measures that follow.

The formula

The exposure level, referenced to 8 hours, is the energetic sum of the individual periods’ contributions weighted by their duration:

$$L_{EX,8h}=10{\log }_{10}\left[\frac{1}{T_0}\sum _i{T}_{e,i}10^{L_{Aeq,i}/10}\right][\mathrm{dB}(\mathrm{A})]$$

T₀      = 8 hours (reference duration)
LAeq,ᵢ  = A-weighted equivalent level of period i
Te,ᵢ    = duration of period i [hours]

The detail that causes the most errors is the divisor: it is always T₀ = 8 hours, not the sum of the actual durations. A cumulative exposure longer than 8 hours therefore yields a LEX,8h higher than the mean LAeq of the shifts; a shorter exposure yields a lower one. It is how the regulation normalises exposures of different duration onto a standard working day.

A worked example

An operator spends 6 hours at the machine tool at 85 dB(A) and 2 hours at the assembly bench at 78 dB(A). The exposure normalised over 8 hours is:

$$L_{EX,8h}=10{\log }_{10}\left[\frac{1}{8}\left(6\cdot 10^{8.5}+2\cdot 10^{7.8}\right)\right]\approx 84.0\mathrm{dB}(\mathrm{A})$$

The 78 dB(A) period, though it lasts two hours, moves the result by a few tenths: 7 dB below the dominant period, its energetic contribution is marginal. The LEX,8h of 84.0 dB(A) falls between the lower and upper action values: information, training and PPE made available apply, but not yet mandatory use.

The 3 dB exchange rate, and the dose that follows

The fixed 8-hour divisor has one consequence worth isolating, because it is the rule most used on site. Since the criterion is purely energetic, every 3 dB halves the permitted time. All of these exposures give the same LEX,8h of 85.0 dB(A):

This is the 3 dB exchange rate, and it is not an arbitrary convention: it follows directly from the energy sum, because a doubling of energy is 10·log₁₀(2) = 3.01 dB. The round 3 dB is the customary rounding, and it is why the table’s rows give 85.0 rather than exactly 85. Worth stating because it is not universal: US OSHA regulation has historically used a 5 dB exchange rate, which is less protective. Comparing assessments made under different criteria without saying so produces incoherent numbers.

Inverting the same relation gives the duration that brings LEX,8h to 87 dB(A), that is to the exposure limit value:

$$T_{\max }=8\cdot 10^{(87-L_{Aeq})/10}\text{hours}$$

Twenty-four minutes at 100 dB(A) shows how little time it takes at the levels found on some percussive-tool work — what level a given machine actually produces depends on the tool, the material, the operator’s position and the room, and has to be measured, not assumed.

Two important qualifications on how this curve is read, because the wrong conclusion is easy to draw.

It is not a legally permitted time. The 87 dB(A) figure is the exposure limit value, and compliance with it is checked taking account of the attenuation of the hearing protectors actually worn (art. 193); the action values, by contrast, refer to the nominal level without PPE. The curve above is computed on the nominal level: it says how long an unprotected exposure would last before accumulating the limit’s energy, not how long the law allows anyone to stay there. A direct consequence for the tool follows: not knowing the PPE attenuation, it cannot by itself attest that the limit value has been exceeded. It can correctly compare the nominal level with 80 and 85 dB(A), and flag that the nominal one exceeds 87; exceeding the limit has to be verified on the effective level at the ear.

Cutting exposure time is a prescribed measure, not an excluded option. Art. 192 expressly lists, among the preventive measures, limiting the duration and intensity of exposure and adopting appropriate working schedules with sufficient rest periods. What the curve shows is that at high levels the time lever alone becomes organisationally impractical — not that it is ruled out. The decree’s hierarchy stands: elimination or reduction at source through technical and organisational measures first, PPE where the risk cannot be sufficiently avoided that way.

How much a secondary period counts

The corollary of the worked example above, quantified. On a shift with 7 hours at 85 dB(A), adding one hour at progressively lower levels:

Beyond 10 dB below the dominant period, a whole hour moves the result by six hundredths of a decibel: less than the resolution the value is reported at. In this example, then, measurement time pays off best concentrated on the noisiest activities, and reducing the noise of secondary ones does not move the outcome until the dominant one is dealt with. It is not a general sampling rule, though: art. 190 requires measurements representative of the exposure, and a quieter activity becomes relevant again when it lasts many hours, is highly variable, adds up across many others, contains impulsive events, or when the worker is already close to a threshold or the dominant activity has already been mitigated. It is the same arithmetic as sound level composition, applied to time instead of sources.

The peak level

Alongside LEX,8h, the peak level L_Cpeak is assessed, in C weighting, which captures the brief impulsive events (blows, bangs) that the energetic average would dilute. For assessment purposes the maximum peak value representative of the exposure is taken: the peak is averaged neither across events nor across days, and moving to weekly exposure does not turn it into a weekly quantity.

Classification — D.Lgs 81/08 Art. 189

The regulation sets three thresholds, each expressed in both LEX,8h and L_Cpeak:

Lower action values    LEX,8h = 80 dB(A)  | LCpeak = 135 dB(C)
Upper action values    LEX,8h = 85 dB(A)  | LCpeak = 137 dB(C)
Exposure limit value   LEX,8h = 87 dB(A)  | LCpeak = 140 dB(C)

For the purpose of applying the obligations, the most onerous threshold reached by either LEX,8h or the peak is taken: it is enough for one of the two to reach an action value for its consequences to apply. The decree does not, however, define an “overall class” for the worker: that is the tool’s reading aid, not a regulatory category.

Obligations by band

Each band carries increasing obligations for the employer:

• Below the lower action values — the additional obligations tied to the action values do not apply, but the general ones remain: the physical-agents risk assessment (art. 181) and elimination or minimisation of the risk (art. 192) apply regardless.
• At the lower action values and above — information and training (art. 195 requires them for exposure equal to or above the lower value); hearing PPE made available (art. 193 ties this to exposure exceeding the lower value); health surveillance on the worker’s request and subject to the occupational physician confirming it is warranted (art. 196 c. 2: the two conditions are conjunctive, not alternative).
• At the upper action values and above — use of hearing PPE mandatory (art. 193 ties this to exposure equal to or above the upper value); programme of technical and organisational reduction measures; periodic health surveillance; area signage, with demarcation and restricted access where technically feasible and justified by the risk.
• Beyond the exposure limit value, assessed with PPE applied — an unacceptable condition: immediate reduction action, investigation of causes, PPE review.

The 87 dB(A) limit value is assessed taking into account the effective attenuation of the hearing personal protective equipment worn; the action thresholds, instead, refer to the nominal exposure, without PPE.

A note on the exact thresholds, which matters when a value lands on one. The obligations do not all use the same comparison operator: information and training apply to exposure equal to or above the lower value, so at exactly 80.0 dB(A) they already apply; making PPE available is tied to exposure that exceeds that value; mandatory use of PPE applies to exposure equal to or above the upper value, so at exactly 85.0 dB(A) it is already active. Software that assigns each band one indivisible package of obligations goes wrong precisely on the boundary values: the obligations have to be checked one at a time, each with its own operator.

Weekly exposure

When exposure varies widely from day to day — on a construction site or in maintenance, for instance — Italian D.Lgs 81/08 (Art. 189, paragraph 2) allows, in duly justified circumstances, using the weekly exposure level L_EX,w instead of the daily one. It applies to both the action values and the limit value, not just to the comparison with the limit.

The principle stays energetic, and it is an average over five nominal eight-hour days — not an arithmetic average of decibels:

$$L_{EX,w}=10{\log }_{10}\left[\frac{1}{5}\sum _{j=1}^{5}10^{L_{EX,8h,j}/10}\right]$$

The decree sets two distinct conditions: that the weekly level, demonstrated by suitable monitoring, does not exceed 87 dB(A); and that adequate measures are taken to minimise the risks. The second is not a monitoring duty, it is a reduction duty. And where the weekly level is itself variable, paragraph 3 requires the maximum recurring weekly level to be used, not the average of the weeks.

It should be kept distinct from the mechanism of art. 191, which covers activities where personal exposure fluctuates widely and allows, under conditions, workers to be assigned an exposure above the upper action values while ensuring the consequent measures. It is not the same thing as L_EX,w. For most cases, in any event, the reference remains the daily LEX,8h.

Limitations

• The computation assumes each period’s LAeq is genuinely representative of the activity; short or unrepresentative sampling leads to distorted estimates. The methodology for determining occupational exposure is governed by ISO 9612 (current edition: 2025).
• It does not compute the interactions between noise and ototoxic agents or mechanical vibration. Do not conclude that they are extraneous: art. 190 c. 1 letter d) requires them to be considered within the noise risk assessment, even though the tool does not handle them.
• PPE attenuation must be assessed separately: the tool computes the “nominal” LEX,8h, without PPE.

A demonstrative tool: it does not replace the noise risk assessment, which art. 181 reserves to qualified personnel within the prevention and protection service, holding specific knowledge in the field. Unlike environmental acoustics, the decree here requires no ENTECA-style professional registration but a substantive qualification.

Standards & references

• Italian D.Lgs 9/04/2008 no. 81 — Consolidated Workplace Safety Act, Title VIII Chapter II (protection of workers against noise exposure risks), Art. 187-198.
• ISO 9612:2025 — Acoustics — Determination of occupational noise exposure: methodology. Supersedes ISO 9612:2009, withdrawn in May 2025.
• ISO 1999:1990 — the definition of LEX,8h in art. 188 refers expressly to this standard.
• Directive 2003/10/EC — minimum safety requirements for workers’ exposure to noise, transposed by D.Lgs 81/08.

The tool is available as a runnable application at /en/tools/lex-8h/.