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The NZ RF field exposure Standard

The New Zealand radiofrequency (RF) field exposure Standard NZS 2772.1:1999 Radiofrequency fields - Maximum exposure levels - 3 kHz to 300 GHz  was developed by a committee appointed by Standards New Zealand. Background information on the development and content of the Standard can be found in a paper presented to the World Health Organisation EMF Project.  

The Standard sets limits on exposures to RF fields in the frequency range covering all RF sources in New Zealand (transmitters and industrial uses), and provides guidance on verification of compliance. The limits are based on Guidelines published in 1998 by the International Commission on Non-Ionising Radiation Protection (ICNIRP), and reaffirmed by ICNIRP in 2009 following a further review of the relevant research.  

Unfortunately, the Standard is not freely available, but has to be purchased from Standards NZ.  However, the numerical limits can be found in the ICNIRP Guidelines (referenced above), and the exposure limits and other content of the Australian Radiation Protection Standard 3 (RPS3) published by the Australian Radiation Protection and Nuclear Safety Agency are very similar in almost all areas.  RPS3 also contains some useful appendices.  

Exposure limits

The Standard sets fundamental exposure limits, called basic restrictions (BRs) in terms of the physical quantities most closely related to effects produced in the body by exposures to RF fields.  Various BRs are used, depending on the RF field frequency.  For example, at frequencies between 100 kHz and 10 GHz (which covers most RF sources of interest) the BR is based on RF power absorbed in the body (specific absorption rate - SAR). The BRs were set by determining (from the research data) the exposure thresholds at which RF fields appear to produce health effects, and applying a safety factor of 10 for occupational exposures and 50 for the public. 

BRs, while well-suited for laboratory work and detailed calculations, are usually not very practical for everyday use.  For this reason, the Standard also specifies reference levels (RLs) in terms of quantities which are readily assessed by calculation or measurement, such as the RF electric and/or magnetic field strengths or the power flux density of the electromagnetic wave.  The RLs are set conservatively so that if exposures comply with them, compliance with the BRs is assured, and in most situations they can be considered as the "exposure limits" in the Standard (although that term is not used as such).  

At many frequencies, the Standard allows exposures to be averaged over 6 minutes, and also averaged over a small area.  The Standard describes how to evaluate exposures when there are RF sources at several frequencies.

In addition to requiring compliance with the numerical limits, for public exposures the Standard also requires "Minimizing, as appropriate, RF exposure which is unnecessary or incidental to achievement of service objectives or process requirements, provided that this can be readily achieved at modest expense".  Effectively this means that if different options are available when selecting and designing a transmitter site, those resulting in the lowest exposures should be chosen, all other things being equal.

Further information

For further information, or to find out the limits which should apply to a particular RF source, get in touch.