How Far Do You Need to Stay From a Transmitting Antenna? RF Exposure Safe Distances Explained (ARPANSA RPS S-1 / ICNIRP)

RF Exposure Safe Distance: The Short Answer

The safe distance from a transmitting antenna is the distance at which the radio frequency power density falls to the ARPANSA exposure limit. For one antenna in its main beam it is r equals √(EIRP / (4π × S_limit)), where EIRP is the radiated power in watts and S_limit is the limit in watts per square metre. It depends on three things only: the radiated power, the frequency (because the limit changes with frequency), and whether the person is a worker or a member of the public (because those two groups have different limits). A typical 900 MHz mobile sector at around 2000 W EIRP reaches the public limit at about six metres on boresight and the occupational limit at under three metres.

Public vs Occupational RF Exposure Limits

ARPANSA defines two populations, and getting them straight is half the job.

The general public limit applies to anyone not trained and informed about their exposure: residents, pedestrians, building occupants, and contractors on the roof for an unrelated trade. The occupational limit applies only to people who are trained, aware of the exposure, and able to manage it, such as a rigger climbing under a permit.

The occupational power density limits are five times higher than the public limits across most of the band, which is why the same antenna produces two different safe distances depending on who is standing in front of it. The occupational limit only holds while those conditions hold; an untrained person is assessed as public no matter where they are.

ARPANSA RPS S-1 and ICNIRP Power Density Limits

In Australia the limits come from ARPANSA RPS S-1, which adopts the ICNIRP 2020 reference levels, so the numbers an Australian engineer works to are the ICNIRP numbers. Carrier licence conditions administered by the ACMA require compliance with that standard.

For antennas at VHF and above, the quantity you compare against the limit is power density in watts per square metre. The limits below are the plane wave equivalent reference levels, with frequency f in megahertz. They start at 30 MHz because below that the limits are written instead as separate electric and magnetic field strengths.

The most restrictive public limit, 2 W/m², sits in the VHF and lower UHF range where the body absorbs energy most efficiently, which is exactly where much two way radio and broadcast operates. At 900 MHz the public limit works out to 900 divided by 200, or 4.5 W/m², and the occupational limit to 900 divided by 40, or 22.5 W/m².

RF Exposure Safe Distance Formula

In the far field, power spreads over the surface of an expanding sphere, so the power density at distance r is:

S = EIRP / (4π r²)

Set that equal to the limit and solve for distance:

r = √(EIRP / (4π × S_limit))

EIRP is in watts, the limit in watts per square metre, and r comes out in metres. This is the standard predictive screening method behind ARPANSA aligned desktop assessments.

Example Calculation at 900 MHz

Take a 900 MHz sector with a licensed EIRP of 2000 W. Using the public limit of 4.5 W/m²:

r = √(2000 / (4π × 4.5)) = √35.4 = 5.95 m

So the public compliance distance is about six metres, measured along the boresight. The same chart of distances, for the public and occupational limits at 900 MHz, looks like this:

These are boresight distances for a single antenna in the far field, which is the worst case direction. Off to the side, above, or below the main beam, the antenna pattern cuts the power sharply and the distance shrinks with it. That is why someone standing on the ground directly under a tower mounted panel is usually exposed to a tiny fraction of the limit: the main beam points out toward the horizon, well above head height.

Why the Simple Formula Is Not the Whole Answer

The chart above is a screening tool. On a real site, four effects move the true boundary, and a defensible assessment accounts for each.

• Sources add together. Almost no site carries one antenna. The standard requires you to sum the fractional exposures, the sum of each source power density divided by its own limit, and keep the total at or below one. Two antennas each at sixty per cent of the limit are not compliant where their beams overlap.
• Exposure is averaged over time. The limits are not instantaneous peaks. Whole body exposure averages over thirty minutes, so a source is assessed at its time averaged maximum power, which accounts for transmission duty and, for 5G, for beamforming and time division duplexing rather than assuming a continuous full power beam everywhere.
• Exposure is averaged over the body. The compliance basis is the whole body spatial average over a two metre vertical line, not the single hottest point in space.
• The near field is different. Within the far field boundary, two times the aperture squared divided by the wavelength, the inverse square formula breaks down. For a small UHF antenna that region is a fraction of a metre; for a large panel or a dish it can be several metres, right where it matters.

RF Exclusion Zones Explained

An exclusion zone is the region around an antenna, or a group of antennas, where the combined power density reaches one hundred per cent of the applicable limit. Inside it, access by the relevant population is controlled. On a multiple antenna site the boundary is set by the summed field of every transmitter, not by any single one.

For workers, the question becomes a vertical route rather than a horizontal distance. A rigger climbing past a live aperture passes through its near field, where the occupational limit can be exceeded within touching distance even when the ground level field is trivial. The control is a permit to work that finds the worst face and peak height on the planned climb and, where the route exceeds the limit, names the sources to switch off or reduce so the whole climb is brought within the occupational limit.

Running an EME Assessment in noIM₃

A hand calculation gives you a first estimate; turning it into summed exclusion zones and a report a regulator will accept is what the RF EME Exposure Modeller is for. A typical assessment runs like this:

1. Import the site from the ACMA register. One search pulls every licensed transmitter with its EIRP, frequency, height, azimuth, and polarisation.
2. Place the antennas on a 3D model of the structure, whether that is a lattice tower, a monopole, a mast, or a rooftop pole.
3. Run the exposure model. It sums all sources, applies the ARPANSA or ICNIRP limits for the chosen population, and handles the time and spatial averaging.
4. Read the exclusion zone off the heatmap and export the report.

From there it also plans worker climbs, apportions cumulative exposure between operators on a shared site, and produces a rigger mounting schedule and a fence setting out sheet. If you only need to check one antenna by hand, the Antenna Power Density calculator runs the exact formula above for a single source, and the EIRP calculator turns transmitter power and antenna gain into the EIRP those formulas need.

Frequently Asked Questions

Is it safe to stand near a mobile phone tower? At ground level, yes, for normal public access. The main beam points out toward the horizon, well above head height, so the field at the base is typically a small fraction of the public limit. The compliance distances matter most directly in front of the antenna and on the structure itself.

How do you calculate the RF exposure safe distance? For one antenna in its main beam, take the square root of the EIRP in watts divided by four pi times the exposure limit in watts per square metre. The limit depends on the frequency and on whether the person is a worker or the public.

What is the difference between public and occupational RF exposure limits? The occupational limit applies only to people who are trained, aware of the exposure, and able to manage it. Everyone else is assessed against the public limit.

Does ARPANSA RPS S-1 use the ICNIRP limits? Yes. RPS S-1 adopts the ICNIRP 2020 reference levels, so the Australian power density limits are the ICNIRP values. The difference is the regulatory framing and the citation, not the numbers.

Key Takeaway

The distance you need to stay from a transmitting antenna is not a fixed number on a sign. It follows from three inputs, the radiated power, the frequency, and the population, run through one far field formula, then corrected for the things a real site does that the formula ignores: many sources summing together, averaging over time and over the body, and a near field that does not obey the inverse square rule. The formula gives a defensible first estimate in seconds. A full EME assessment turns that estimate into exclusion zones, worker access controls, and compliance documentation you can submit to regulators and site owners.