🌿 Noise in the working environment — the exposure level referred to an 8-hour working day

Environment PN-N-01307

Overview

The assessment of the exposure to noise in the working environment is based on three quantities: the equivalent continuous A-weighted sound pressure level (LAeq,T), the maximum A-weighted sound pressure level (LAmax) and the peak C-weighted sound pressure level (LCpeak). It is considered that it is precisely these that have a decisive influence on the occurrence of damage to hearing. The equivalent continuous A-weighted sound pressure level converted to the standardised daily working time is called the noise exposure level referred to an 8-hour working day (LEX,8h); its weekly counterpart is LEX,w.

Routine measurements of noise at workplaces are carried out in accordance with PN-N-01307:1994 and PN-EN ISO 9612 (available in the Polish version since 2011). Integrating-averaging sound level meters are used for them, placed at the measurement points or held in the hand by a person following the worker, or personal sound exposure meters (noise dosimeters) worn by the workers. Contemporary integrating meters determine LAeq,T, LAmax and LCpeak simultaneously, over the duration of the measurement T.

The maximum admissible intensity (NDN) values of noise with regard to the protection of hearing are laid down by the regulation on the maximum admissible concentrations and intensities of agents harmful to health in the working environment, and they are independent of the character of the work performed: LEX,8h and LEX,w = 85 dB, LAmax = 115 dB, LCpeak = 135 dB. For pregnant women a lower value of LEX,8h = 65 dB is in force. Independently of the criterion of the protection of hearing, the standard PN-N-01307 gives admissible values of the equivalent continuous A-weighted sound pressure level with regard to the possibility of performing the basic activities of the work — e.g. 55 dB for mental work requiring concentration.

Method principle

The sound level meter measures the sound pressure corrected with the A frequency weighting (reproducing the sensitivity of the ear) and averages it energetically over the time T — the result is LAeq,T, that is the level of a sound of constant level with which, over the same time, the same acoustic energy is associated as with the variable noise tested. LAmax is the maximum r.m.s. value of the A-weighted sound pressure level averaged with the time constant S (slow); LCpeak is the maximum instantaneous value of the C-weighted sound pressure level, of importance with impulsive noise. The exposure level LEX,8h is obtained by referring the LAeq,Te measured over the effective time of exposure Te to the reference time To = 8 h; where the day is divided into tasks with different exposures, the contributions of the individual tasks weighted by their duration are added energetically.

Applications

• Measurements of harmful agents at workplaces required by the health and safety regulations — comparison with the NDN (85 dB for LEX,8h)
• Assessment of the exposure of groups of workers with a homogeneous exposure (patrolling staff, truck operators, machine operators)
• Assessment of the workplaces of pregnant women (LEX,8h ≤ 65 dB) and of young persons
• Assessment of the nuisance of noise in rooms of mental work (LAeq,Te ≤ 55 dB in accordance with PN-N-01307)
• Selection of hearing protectors and planning of measures limiting noise

Key parameters

Standard

Standard number

PN-N-01307:1994

Title (PL)

Hałas — Dopuszczalne wartości hałasu w środowisku pracy — Wymagania dotyczące wykonywania pomiarów

Title (EN)

Noise — Permissible noise values in the work environment — Requirements for performing measurements (norma krajowa)

Step-by-step procedure

1. Analysis of the conditions of work

   Establish the sources of noise and the range of the tasks performed in exposure; where it is of importance, distinguish groups of workplaces with a homogeneous exposure. On that basis choose the measurement strategy in accordance with PN-EN ISO 9612: 1 — task-based measurements, 2 — job-based measurements, 3 — full-day measurements.

2. Check of the apparatus

   At the beginning of the day of measurement and before every series check the meter with a class 1 acoustic calibrator in a quiet place, and if need be adjust the measuring channel. The instruments must be calibrated at a calibration laboratory at intervals not longer than 2 years.

3. Position of the microphone

   Measure at the place where the head of the worker usually is, or — where his presence is indispensable or where a dosimeter is used — at a distance of about 10–40 cm from the canal of the external ear on the side of the ear exposed to the higher sound level.

4. Strategy 1 — task-based measurements

   For each task make a series of N ≥ 3 measurements (samples) of the same duration Tp: for short tasks Tp equal to the duration of the task, for long ones Tp ≥ 5 min, for cyclical ones Tp = 3 × the duration of the cycle. If the results differ by 3 dB or more, increase the number of measurements to N ≥ 6, lengthen Tp or divide the day into more tasks. Determine the duration of each task Tm from an interview, from observation or from at least three measurements of the time.

5. Strategy 2 — job-based measurements

   For a group with a homogeneous exposure establish the minimum total time of the measurements depending on the size of the group (e.g. 5 h with a group of up to 5 persons) and make K ≥ 5 samples distributed at random over the time of the shift and among the members of the group; the measurements may cover several shifts and different phases of the day.

6. Strategy 3 — full-day measurements

   Choose representative days and make with the dosimeter at least 3 measurements covering the whole shift or a substantial part of it; with a spread of LAeq ≥ 3 dB increase the number of measurements by at least 2 (K ≥ 5).

7. Check after the series

   After the end of the series check the meter again with the calibrator, without adjustment. If the difference of the readings before and after the series exceeds 0.5 dB, reject the results of the series.

8. Calculation of LEX,8h and assessment

   Refer the LAeq,Te to the reference time of 8 h; where the day is divided into tasks, add energetically the contributions of the tasks weighted by the time Tm. Compare the result together with LAmax and LCpeak with the admissible values (85 / 115 / 135 dB). Estimate the uncertainty in accordance with the approach described in PN-EN ISO 9612 for the strategy chosen.

Required equipment and apparatus

Health and safety (OHS)

• The person making the measurements in zones of noise ≥ 85 dB uses hearing protectors — the measurement does not release anyone from the duty of protection
• Carry out measurements at machines in agreement with the operator, without interfering with the dangerous zones of the equipment
• With impulsive noise pay attention to LCpeak — a single event may exceed 135 dB in spite of a low LEX,8h

Frequently asked questions