🌿 Electromagnetic field in the working environment — electric field strength E and magnetic field strength H, protection zones

Environment PN-T-06580-3

Overview

An electromagnetic field (EM field), the components of which are the electric field (E field) and the magnetic field (M field), is a physical agent of the working environment of a frequency of 0 Hz – 300 GHz; it is characterised by the electric field strength (E, V/m; alternatively the charge Q for f < 5 Hz), the magnetic field strength (H, A/m; alternatively the induction B, T) and the frequency f. Every electrical device is a source of a field; in the working environment the significant ones include supply installations, transformers, industrial devices (induction heaters, welders), medical devices, transmitters and base stations. A field induces electric currents in the body and heats the tissues (the thermal effect).

The Polish regulations lay down, in the regulation on maximum admissible concentrations and intensities (NDS and NDN, part E), the limits of the Intervention Exposure Levels (IPN) — the operational ones: base, upper and lower, and the supplementary ones: auxiliary, peak and local — given in tables 13 (E field) and 14 (M field) as a function of the frequency. On their basis the protection zones are determined: the danger zone (E ≥ IPNog-E or H ≥ IPNog-H), the hazard zone (from IPNod to IPNog) and the intermediate zone (from IPNp to IPNod); a field below IPNp is the safe zone. Only workers employed at the sources may be present in the fields of the protection zones, after training and medical examinations (occupational exposure). The requirements for the assessment of the EM field and for the protective measures are laid down by the regulation of the Minister of Family, Labour and Social Policy of 29 June 2016 on occupational health and safety in work involving exposure to an electromagnetic field. The terminology (part 1) and the methods of measurement and assessment of the field at the workplace (part 3) are given by the standard PN-T-06580:2002, harmonised with the regulation on the NDN.

Method principle

The exposure is assessed on the basis of measurements of the root-mean-square value of the electric or the magnetic field strength; the result is taken to be the maximum instantaneous root-mean-square value measured along the line corresponding to the axis of the worker's body, from the ground to a height of 2 m. The field measured is that undisturbed by the presence of a person (the primary field) — at the places where workers are present, but in their absence and with no other persons in the measurement area — under operating conditions of the source giving the maximum strengths (or else the possibility of greater exposures is taken into account in the analysis). The meters consist of interchangeable probes with a sensor of the electric or of the magnetic field (multi-turn coils, dipoles, Hall sensors) and a battery-powered monitor; measurement of the root-mean-square value (RMS), isotropic measurement and a flat frequency characteristic of the sensitivity within the measuring band are required, and the instruments are subject to periodic checking in reference fields. The IPN limits apply to the maximum local values of E and H averaged in a cube of 10 cm edge (the equivalent of a non-directional measurement); in the time domain the peak, the equivalent or the root-mean-square value is used (for 100 kHz – 6 GHz T_RMS = 6 min). The result is compared with the limits for the frequency identified; for composite fields the harmonic components are taken into account according to the rules of the standard, and where there is a large variability in time the measurement is supplemented by recording.

Applications

• Control and periodic measurements of the EM field at workplaces required by the regulation of the Minister of Health — after the commissioning of a source, periodically where protection zones occur and after every change in the operating conditions of the source
• Determination of the extent of the protection zones at industrial devices and supply installations (transformers, switching stations, heavily loaded cables)
• Workstations at medical devices which are sources of fields and at the aerials of radio and television transmitters and of mobile telephony base stations
• Assessment of the exposure in office rooms where a workstation adjoins a switching station, heavily loaded cables or aerials — in typical offices the levels are below 0.1 of the limits and no measurements are carried out
• Assessment of occupational risk and classification of the exposure as occupational or non-occupational

Key parameters

Standard

Standard number

PN-T-06580-3:2002

Title (PL)

Ochrona pracy w polach i promieniowaniu elektromagnetycznym o częstotliwości od 0 Hz do 300 GHz — Część 3: Metody pomiaru i oceny pola na stanowisku pracy

Title (EN)

Occupational protection in electromagnetic fields and radiation of frequency from 0 Hz to 300 GHz — Part 3: Methods of measurement and assessment of the field at the workplace

Step-by-step procedure

1. Identification

   Identify the sources of the field (from the technical documentation or by experimental measurement), their frequencies, modes and operating conditions and the places where workers are present. Establish whether the previous two measurements did not exceed 0.1 of the admissible values — the measurements may then be dispensed with.

2. Selection and checking of the meters

   Select the probes for the frequency range and the expected strengths (RMS, isotropic, a flat characteristic, immunity to fields of other frequencies); check that the calibration in reference fields is up to date. The measurements are carried out by an accredited laboratory.

3. Conditions of measurement

   Start up the source under the conditions giving the maximum strengths (maximum load, all devices switched on, a time of increased current consumption). Remove the workers and other persons from the measurement area — it is the primary field that is measured.

4. Measurement

   At every place where a worker is present measure E and H along the axis of the body from the ground to 2 m and take the maximum instantaneous root-mean-square value; with composite fields measure broadband, and where the result exceeds about 50 % of the reference value — carry out a spectral analysis and take the harmonic components into account. Where there is a large variability in time supplement it by recording.

5. Determination of the zones

   Compare the results with the IPN limits for the frequency identified (tables 13 and 14); determine and mark out the extent of the danger, the hazard and the intermediate zones around the source; the area below IPNp is the safe zone.

6. Assessment and documentation

   Classify the exposure (occupational in the protection zones — only trained workers with medical examinations; non-occupational outside the zones) and, where required, estimate the indices of exposure from the time of presence. Draw up a test report with a sketch of the zones, the operating conditions of the sources and the instruments; repeat the measurements after every change in the operating conditions of the source.

Required equipment and apparatus

Health and safety (OHS)

• The person carrying out the measurements at strong sources is himself exposed — bring the probe up on an extension arm, limit the time spent in the hazard zone, do not enter the danger zone without means of protection
• Persons with medical implants (pacemakers, pumps) may not carry out measurements in the protection zones

Frequently asked questions