Source: https://jmrplens.github.io/phonometry/guides/occupational-exposure/ # Occupational Noise Exposure (ISO 9612) A working day is rarely measured in one take: the daily exposure level a regulation acts on has to be assembled from *samples* of a real shift, and reported with an uncertainty a hygienist can defend. `lex_8h` (in [Levels](https://jmrplens.github.io/phonometry/reference/api/levels/levels/)) turns *one* recording into a daily level. ISO 9612:2009, the engineering method (accuracy grade 2), is the survey design *around* that primitive: how to sample a real working day, how to combine the pieces, and how to attach the normative uncertainty every occupational-hygiene report needs. The `occupational_exposure` module adds the three **measurement strategies** and the **Annex C** uncertainty budget on top of the energy-average machinery. ## 1. The three measurement strategies (Clauses 9-11) The *task-based* strategy (Clause 9) splits the nominal day into tasks, takes $I \ge 3$ samples per task, and energy-sums the task contributions $$ L_{EX,8h,m} = L_{p,A,eqT,m} + 10 \log_{10}(T_m/T_0), \qquad T_0 = 8\ \text{h}, $$ so a loud but short task contributes little. The *job-based* (Clause 10) and *full-day* (Clause 11) strategies instead take $N \ge 5$ (or three whole-day) random samples over a homogeneous exposure group and normalise the effective-day duration. The daily level is the same either way; the strategies differ in how the **uncertainty** is built. **Choosing a strategy.** ISO 9612 Table B.1 picks the strategy from the *work pattern*, not from convenience, and the trade-off is coverage against effort. The **task-based** strategy is the recommended default when the day decomposes into a small number of well-defined tasks: because it measures each task separately, it explains *where* the dose comes from (the per-task breakdown above) and lets a short, loud task be sampled properly without dragging out the whole survey, but it needs a reliable work analysis, and its uncertainty grows if the task durations are themselves uncertain. The **job-based** strategy suits a mobile worker with an unpredictable pattern or a homogeneous group doing "the same job": random samples across the group average over the variability instead of resolving it, which is robust when the day cannot be cleanly cut into tasks but blind to which activity dominates. The **full-day** strategy (a worn dosimeter capturing the entire shift, repeated on several days) needs the least analysis and captures everything including the unexpected, at the cost of the most wearer-days and the weakest diagnostic value (one number per day, no breakdown, and false contributions like knocks on the microphone are hard to spot). As a rule: resolve the dose with task-based when you can, fall back to job-based for irregular work, and use full-day when the pattern defies description or an independent whole-shift check is wanted. ```python from phonometry import hearing # ISO 9612 Annex D — a welder's day split into three tasks. Each task level is # the energy average of its Lp,A,eqT samples; durations carry a measured range. tasks = [ hearing.Task(samples=(70.0,), duration_hours=1.5, label="planning/breaks"), hearing.Task(samples=(80.1, 82.2, 79.6), duration_hours=5.0, duration_range=(4.0, 6.0), label="welding"), hearing.Task(samples=(86.5, 92.4, 89.3, 93.2, 87.8, 86.2), duration_hours=1.5, duration_range=(1.0, 2.0), label="cutting/grinding"), ] res = hearing.task_based_exposure(tasks, include_duration_uncertainty=False, warn=False) print(f"LEX,8h = {res.lex_8h:.1f} dB U = {res.expanded_uncertainty:.1f} dB") # LEX,8h = 84.3 dB U = 2.7 dB print(f"one-sided 95 % upper limit LEX,8h + U = {res.upper_limit:.1f} dB") # 87.0 dB for t in res.tasks: print(f" {t.label:<16} Lp,A,eqT = {t.lp_aeqt:5.1f} contributes {t.lex_8h_contribution:5.1f} dB") # planning/breaks Lp,A,eqT = 70.0 contributes 62.7 dB # welding Lp,A,eqT = 80.8 contributes 78.7 dB # cutting/grinding Lp,A,eqT = 90.1 contributes 82.8 dB # The same shift measured job-based (Annex E) and full-day (Annex F): both use # the Eq C.9 / Table C.4 sampling budget with k = 1.65 (one-sided 95 %). job = hearing.job_based_exposure([88.1, 86.1, 89.7, 86.5, 91.1, 86.7], effective_duration_hours=7.5) full = hearing.full_day_exposure([88.0, 91.9, 87.6, 90.4, 89.0, 88.4], effective_duration_hours=9.25) print(f"job LEX,8h = {job.lex_8h:.1f} dB U = {job.expanded_uncertainty:.1f} dB") # job LEX,8h = 88.2 dB U = 3.8 dB print(f"full-day LEX,8h = {full.lex_8h:.1f} dB U = {full.expanded_uncertainty:.1f} dB") # full-day LEX,8h = 90.1 dB U = 3.4 dB res.plot() # the figure below: task contributions with LEX,8h and LEX,8h + U ```

Show the code for this figure

```python import matplotlib.pyplot as plt from phonometry import hearing # The ISO 9612 Annex D welder's day of the previous snippet. tasks = [ hearing.Task(samples=(70.0,), duration_hours=1.5, label="planning/breaks"), hearing.Task(samples=(80.1, 82.2, 79.6), duration_hours=5.0, duration_range=(4.0, 6.0), label="welding"), hearing.Task(samples=(86.5, 92.4, 89.3, 93.2, 87.8, 86.2), duration_hours=1.5, duration_range=(1.0, 2.0), label="cutting/grinding"), ] res = hearing.task_based_exposure(tasks, include_duration_uncertainty=False, warn=False) # One line: task contribution bars plus the LEX,8h and LEX,8h + U lines. res.plot() plt.show() ```

## 2. The Annex C uncertainty budget Two subtleties are worth spelling out. First, the coverage factor is $k = 1.65$ for a **one-sided** 95 % interval (Clause 14), because a hygienist cares only about the *upper* bound: `res.upper_limit` = $L_{EX,8h} + U$ is the value 95 % of measurements fall below, the number compared against an action limit. Second, the task and job methods weight the *same* spread of samples differently. The task sampling uncertainty $u_{1a}$ (Eq. C.6) divides the summed squared deviations by $I(I-1)$ (the standard error of the mean, smaller by a factor $\sqrt{I}$), whereas the job/full-day sampling uncertainty $u_1$ (Eq. C.12) is the plain sample standard deviation with denominator $N-1$, whose contribution $c_1 u_1$ is then read from **Table C.4** as a function of $(N, u_1)$. The same raw scatter therefore inflates the job estimate more, which is the standard's built-in penalty for coarser, fewer samples. (The printed job $L_{EX,8h}$ is $88.2$ dB where Annex E reports $88.1$: the standard rounds the effective-day level to $88.4$ before the duration normalisation; the library keeps it unrounded.) **What dominates the budget.** Annex C combines four sources in quadrature (Table C.1): the **sampling** uncertainty ($u_{1a}$/$u_1$), the **duration** uncertainty ($u_{1b}$, task-based only), the **instrument** ($u_2$, Table C.5) and the **microphone position** ($u_3$, Clause C.6). The last two are small and roughly fixed ($u_2 = 0.7$ dB for a class 1 sound level meter, 1.5 dB for a class 2 meter or a personal exposimeter, and $u_3 = 1.0$ dB by default), so in practice the **sampling term almost always dominates**: it scales with the scatter of the measured levels, which in a real workplace easily reaches several decibels and, entered in quadrature, swamps the sub-decibel instrument and position terms. The practical consequence: a quadrature budget is set by its largest term, so tightening the instrument grade buys little once sampling scatter is large; the productive move is *more samples* (the standard error falls as $1/\sqrt{I}$ or $1/\sqrt{N}$), which is exactly what the Clause 9.3 / 10.4 advisories nudge you toward. Because peak $L_{p,Cpeak}$ carries no Annex C sampling model (Table C.5, Note 1), it is reported without an uncertainty, not with a zero one. When a task's samples span **3 dB or more** (Clause 9.3), or the job contribution $c_1 u_1$ exceeds 3.5 dB (Clause 10.4), or too few workers are covered (Table 1 cumulative-duration), the result sets `sampling_advisory=True` and, with `warn=True`, emits an `OccupationalExposureWarning` recommending more measurements. Peak levels $L_{p,Cpeak}$ are reported **without** an uncertainty: Annex C gives no method for them (Table C.5, Note 1), so peak-uncertainty is out of scope. The three Annex D/E/F worked examples above are reproduced to the standard's printed precision (Annex E's final rounding is disclosed above), and the theory is derived on the [Theory](https://jmrplens.github.io/phonometry/reference/theory/environment-transport/) page. ### `task_based_exposure()` / `job_based_exposure()` / `full_day_exposure()` parameters | Parameter | Applies to | Type | Units | Range / default | Notes | | :--- | :--- | :--- | :--- | :--- | :--- | | `tasks` | task | list of `Task` | — | ≥ 1 | Each `Task` has `samples`, `duration_hours`, optional `duration_range`/`duration_samples`, `label`, `instrument` | | `samples` | job / full-day | sequence | dB | ≥ 2 (≥ 5 / ≥ 3 advised) | Random `Lp,A,eqT` samples | | `effective_duration_hours` | job / full-day | float | h | > 0 | Effective working-day duration $T_e$ | | `instrument` | all | str | — | `'class1'`, `'class2'`, `'personal_exposimeter'` (default) | Selects $u_2$ (Table C.5) | | `u3` | all | float | dB | default `1.0` | Microphone-position uncertainty (Clause C.6) | | `include_duration_uncertainty` | task | bool | — | default `True` | `False` omits the $(c_{1b}u_{1b})^2$ term (Annex D case a) | | `n_workers` / `sample_duration_hours` | job | int / float | — / h | default `None` | Table 1 cumulative-duration check | | `warn` | all | bool | — | default `True` | Emit `OccupationalExposureWarning` for the sampling advisories | All three return an `ExposureResult` with `lex_8h`, `combined_standard_uncertainty` $u$, `expanded_uncertainty` $U = 1.65\ u$, `upper_limit` = $L_{EX,8h} + U$, `sampling_advisory`, and (task-based) the per-task `tasks` breakdown; the result's `.plot()` draws the per-task contribution bars with the $L_{EX,8h}$ and upper-limit lines (task-based results only, since the other strategies carry no per-task breakdown). ## 3. The measurement report (`.report()`) ISO 9612 Clause 15 lists what the measurement report shall state, down to the requirement that the noise exposure level and the measurement uncertainty be reported as *separate values*, each rounded to one decimal place. `ExposureResult.report(path)` writes that report as a one-page PDF fiche laid out like a prevention-service measurement sheet: the standard-basis line naming the applied strategy, a header grid (company via `client`, worker(s)/job via `specimen`, workplace via `test_room`, and the Clause 15 c `instrumentation` and `calibration` free-text fields of `ReportMetadata`), the work analysis (the per-task table with the contribution chart for a task-based result, or the sampling summary with the Formula C.9 budget for job-based/full-day), the boxed $L_{EX,8h}$ with $U$, $k = 1.65$ and the one-sided 95 % upper limit, an assessment table against the exposure action values (80/85 dB(A)) and the exposure limit value (87 dB(A)) of Directive 2003/10/EC with a PASS/FAIL verdict against the limit value, and a footer identity block. A printed note records that the limit value applies to the effective exposure with the worn hearing protectors' attenuation taken into account, which the measured $L_{EX,8h}$ does not include. `verbose=True` adds the per-task Annex C uncertainty columns ($u_{1a}$, $u_{1b}$, $u_2$); `language="es"` renders the Spanish fiche (nivel de exposición diario equivalente, comma decimals). Rendering needs the optional `phonometry[report]` extra (reportlab), plus matplotlib for the task-based chart. ```python from phonometry import hearing, ReportMetadata res = hearing.task_based_exposure(tasks, warn=False) # the Annex D day above res.report( "lex8h.pdf", metadata=ReportMetadata( client="Example fabrication works", specimen="Welders (homogeneous exposure group, 4 workers)", test_room="Steel assembly hall, line 2", instrumentation="Personal sound exposure meter (IEC 61252), s/n 0042", calibration="Calibrator IEC 60942 class 1; field checks within 0.3 dB", report_id="EXAMPLE-9612", ), ) # LEX,8h = 84.3 dB, U = 3.2 dB -> lower action value exceeded, limit PASS ``` The rendered example fiche, regenerated with `make reports`, is kept in the repository. Click the preview to open the PDF: [](https://raw.githubusercontent.com/jmrplens/phonometry/main/.github/reports/iso9612_exposure_example.pdf) *Occupational noise-exposure fiche (`ExposureResult.report`), the ISO 9612 Annex D task-based day with the Directive 2003/10/EC assessment.* ## See also - [Levels](https://jmrplens.github.io/phonometry/reference/api/levels/levels/): the `lex_8h` / `sound_exposure` dose primitives (IEC 61252) and the LCpeak these strategies report alongside. - [Measurement uncertainty](https://jmrplens.github.io/phonometry/guides/gum-uncertainty/): the GUM machinery behind combined and expanded uncertainties. - [Theory](https://jmrplens.github.io/phonometry/reference/theory/environment-transport/): the derivation of the strategy formulas and the Annex C budget. - API reference: [`hearing.occupational_exposure`](https://jmrplens.github.io/phonometry/reference/api/hearing/occupational-exposure/). ## References - International Organization for Standardization. (2009). *Acoustics — Determination of occupational noise exposure — Engineering method* (ISO 9612:2009). [iso.org catalogue](https://www.iso.org/standard/41718.html). The implemented method: the three strategies, the microphone placement of Clause 12.3, the Annex C uncertainty budget and the Annex D/E/F worked examples. - European Parliament and Council. (2003). *Directive 2003/10/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise)*. Official Journal of the European Union. [eur-lex.europa.eu](https://eur-lex.europa.eu/eli/dir/2003/10/oj/eng). The EU exposure action values (80/85 dB) and limit value (87 dB) that the `LEX,8h` and its upper limit are assessed against. - National Institute for Occupational Safety and Health. (1998). *Criteria for a recommended standard: Occupational noise exposure — Revised criteria 1998* (DHHS/NIOSH Publication No. 98-126). [doi:10.26616/NIOSHPUB98126](https://doi.org/10.26616/NIOSHPUB98126), [free PDF](https://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf). The freely available criteria document behind the 85 dB(A) recommended exposure limit and the hearing-conservation rationale for measuring the daily dose. ## Standards ISO 9612:2009, *Acoustics — Determination of occupational noise exposure — Engineering method*: the task-based (Clause 9), job-based (Clause 10) and full-day (Clause 11) strategies, the Annex C uncertainty budget (Formulae C.6, C.9 and C.12, Tables C.4/C.5) and the one-sided coverage factor k = 1.65 (Clause 14), validated against the worked examples of Annexes D, E and F.