🌿 Ultrasonic noise at workplaces — measurement in the one-third octave bands 10–40 kHz

Environment PN-Z-01339

Overview

Ultrasonic noise is noise in whose spectrum there occur components of high audible and low ultrasonic frequencies — from 10 kHz to 40 kHz; it figures in the list of harmful physical agents of the working environment. Its main sources are low-frequency ultrasonic technological devices (cleaning baths — 2/3 of the devices in industry, welders, eroders, soldering irons, soldering baths, scalers, ultrasonic guillotines and curtains; the rated frequency usually 18–40 kHz) and machines at which ultrasound arises as a by-product (compressors, burners, valves, pneumatic tools, plasma cutting, high-speed and textile machines). The levels of the ultrasonic components at the workplaces where cleaning baths are operated reach 135 dB, at welders — 140 dB, at non-technological sources — 115 dB. The method of measurement was worked out at CIOP-PIB as a measurement procedure published in 2015, and since 2020 it has been laid down by the standard PN-Z-01339:2020-12, which covers also the corrections for the metrological characteristics of the apparatus and for the influence of the protective grid of the microphone and the estimation of the uncertainty. The admissible values (NDN — the maximum admissible intensity) are laid down by the regulation of the Minister of Family, Labour and Social Policy of 12 June 2018 (Dz.U. 2018 poz. 1286 [Journal of Laws 2018, item 1286]): the equivalent sound pressure levels referred to the 8-hour daily or to the average weekly working time and the maximum levels in the one-third octave bands 10–40 kHz — in force simultaneously; lower values are in force for young persons and for pregnant women. In 2025 CIOP-PIB proposed lowering the NDN in the 20 kHz band from 90 to 85 dB and introducing action levels.

Method principle

The quantities measured are the equivalent (referred to the duration of the given task) sound pressure level and the maximum sound pressure level in seven one-third octave bands with centre frequencies of 10; 12.5; 16; 20; 25; 31.5 and 40 kHz. Workplaces with ultrasonic noise are usually stationary, and the tasks can be divided into distinct intervals of time depending on the operation of the devices, which is why the task-based method of PN-EN ISO 9612 is the most effective (the job-based and the full-day strategies are permitted as well). The measurements are made in the presence of the worker, with the microphone about 10 cm from the entrance to the external ear canal on the side of the more exposed ear; for each task at least three measurements, and the total time of the tasks covers the full shift. The equivalent level for a task is the energy average of the measurements, the maximum one — the greatest of the maximum values. The readings are corrected by the formula Lfi = L′fi + Kap,fi − Kg,fi (the instrument correction and the correction for the protective grid of the microphone), after which the level referred to 8 h is calculated: Lfi,eq,8h = 10 log Σ(Tm/T0)·10^(0.1·Lfi,eq,Tm), T0 = 8 h; with an uneven exposure during the week — the level referred to the working week. The assessment consists in a comparison with the NDN in each band; the exceeding of a single value is enough. The multiple of the NDN: k = 10^((Leq,8h,zm − Leq,8h,dop)/10) for the equivalent levels and k = 10^((Lmax,zm − Lmax,dop)/20) for the maximum ones; the greatest multiple determines the occupational risk: k < 0.5 — small, 0.5 ≤ k ≤ 1 — medium, k > 1 — large. Apparatus: a meter with spectral analysis of class 1 in accordance with PN-EN 61672-1, one-third octave filters 10–40 kHz in accordance with PN-EN 61260, the LIN weighting over the range of the filters; a check of conformity with the standards at least once every two years, an acoustic calibrator before and after the measurements.

Applications

• Assessment of the exposure of the operators of ultrasonic cleaning baths, welders, eroders and soldering irons and of dental scalers
• Workplaces at compressors, pneumatic tools, plasma cutting, high-speed and textile machines (non-technological sources)
• Measurements of harmful agents required by the regulation of the Minister of Health on tests and measurements of harmful agents — the frequency as for audible noise
• Assessment of the occupational risk (the multiple of the NDN) and selection of hearing protectors in the bands 10, 12.5 and 16 kHz
• Checking of the effectiveness of enclosures and screens (a reduction of 40–60 dB) and of the remote control of the process

Key parameters

Standard

Standard number

PN-Z-01339:2020-12

Title (PL)

Hałas ultradźwiękowy — Wymagania dotyczące wykonywania pomiarów w środowisku pracy

Title (EN)

Ultrasonic noise — Requirements for measurements in the working environment

Step-by-step procedure

1. Analysis of the work

   Identify the sources of ultrasonic noise and divide the working time into tasks distinguishable with regard to the noise (the task-based method of PN-EN ISO 9612), so that the total time of the tasks covers the full shift; take into account the typical conditions of operation of the devices.

2. Preparation of the apparatus

   Use a class 1 meter with one-third octave filters 10–40 kHz and the LIN weighting, checked for conformity with the standards not more than 2 years ago; calibrate the measuring channel with an acoustic calibrator before the measurements.

3. Measurements

   In the presence of the worker place the microphone about 10 cm from the entrance to the canal of the more exposed ear; for each task make at least three measurements of the equivalent and of the maximum sound pressure level in each of the seven one-third octave bands.

4. Corrections

   Correct the readings in each band by the instrument correction Kap and by the correction for the protective grid of the microphone Kg (Lfi = L′fi + Kap − Kg); after the measurements repeat the check with the calibrator.

5. Calculations

   For each task calculate the energy-averaged equivalent level and select the greatest maximum level; determine the level referred to 8 h (or to the week with an uneven exposure) in each band; estimate the uncertainty in accordance with the standard.

6. Assessment

   Compare the equivalent and the maximum levels in each band with the NDN from the regulation (the values are in force simultaneously); calculate the multiples k and on the basis of the greatest one classify the risk (small/medium/large); where the NDN is exceeded plan technical and organisational measures and personal protection.

Required equipment and apparatus

Health and safety (OHS)

• The person making the measurement is exposed to the same noise — use hearing protectors and limit the time spent at the source; ultrasound penetrates also through the whole surface of the body
• Do not touch the vibrating transducers, the sonotrodes or the liquid being sonicated (the contact route)

Frequently asked questions