UNDERSTANDING RADIO FREQUENCY (RF) RADIATION EXCLUSION ZONES
- What are RF radiation exclusion zones?
- Understanding exclusion zones.
- Common antenna types and their exclusion zones.
Countries globally have adopted science-based basic restrictions and imposed derived specific reference levels for occupational and general exposure to RF Electromagnetic Fields (EMFs). Measures have also been implemented to address sources or practices that may give rise to RF exposure and the duration of such exposure. These restrictions and measures, when implemented, take the form of public and occupational regions to be avoided about transmitting antennas, more generally referred to as exclusion zones. Visually, a public exclusion zone is usually depicted on a sign or graphic as a yellow solid, cross-hatched or semi-transparent area wherein the Public reference levels would be exceeded if entered, and likewise, an Occupational exclusion zone is depicted as a red solid, cross-hatched or semi-transparent area, again whereing the Occupational reference levels would be exceeded if entered. In this article we will cover:
Understanding RF hazards and the accompanying safe work practices are important for anyone who is going to work on or near a transmitting antennas, whether directly, or indirectly such as HVAC technicians, window washers, water proofing specialists or any other profession accessing rooftops.
1. What are RF radiation exclusion zones?
The area where the RF field values radiating from the antennae exceed the International Commission on Non-Ionizing Radiation Protection’s (ICNIRP) Public reference levels is referred to as the Public exclusion zone. Where it exceeds the ICNIRP Occupational reference levels is known as the Occupational exclusion zone. Put simply, an exclusion zone is a region around an RF transmitting antenna where the general public or occupational workers are not allowed to enter or remain for protracted periods of time as the regulated RF EMF exposure levels would be exceeded inside this zone.
2. Understanding exclusion zones.
The shape of an exclusion zone is determined by the transmitting antenna’s characteristics, whether it be a high gain antenna such as a parabolic dish giving a pencil bean shape exclusion zone, or an omni direction antenna having a donut shaped exclusions zone. The size of the exclusion zone is dependant on the total amount of power being transmitted by the antenna in all bands, and in certain cases where there are collocated antennas these zones combine as such creating larger compound exclusion zones.
Exclusion zones are usually calculated considering free space conditions; however, walls, reflecting objects and barriers amongst others can affect the overall antenna performance, and accordingly the exclusion area. As 5G technologies, especially mmWave, require higher power levels to achieve the performance benefits thereof the impact thereof is larger exclusion zones about these antennas. Additionally, the benefits of 5G also call for a much higher density of these antennas, often even concealing them placing those working nearby such concealed antennas at risk of RF overexposure.
3. Common antenna types and their exclusion zones
Let’s focus on three types of antennas and their exclusion zones namely, the multiband low-gain omnidirectional antenna, the ceiling-mounted indoor antenna and the macrocell sector antenna.
The multiband low-gain omnidirectional antenna is one of the most popularly used antennas in wireless applications. It is typically used for portable and two-way radios and emits equal radio power in all directions from the vertical axis. It has a broad radio-wave beam width that allows the signal to transmit reasonably well and is more reliable irrespective of the terrain. The exclusion zones antennas about the antenna, when the power levels are sufficienty high looks like a donut centred on the vertical axis of the antenna.
Ceiling-mounted indoor antennas are usually found in areas such as shopping centres, underground parking lots, and airports where mobile usage is high and/or where the larger site provides inadequate coverage. These antennas are, when correctly installed, configured to only radiate a low amount of power, and the zones about it would resemble a hemisphere with radius of 1-2ft or 0.5m. Incorrectly installing these could however cause higher power into them, which would then have the zone size much larger and potentially reaching down into areas where members of the general public could inadvertently be passing through them.
Macrocell sector antennas are popular for mobile base stations and are typically mounted on ground-based masts, rooftops, and other existing structures, at a height that ensures a clear view over the surrounding buildings and terrain. Macrocell sector antennas are usually found in rural areas or along highways. These zones resemble a duck bill extending outward from the frontside of the antenna with no zone behind them, or directly beside them. A good rule of thumb would be to not approach closer than 3-5m, 10-15ft directly in front of these without a Personal RF monitor.
Site owners and companies employing RF workers should ensure that they understand the potential limitations and adhere to the exposure guidelines to manage their liability and ensure a safe working environment. Look out for our next article where we will discuss how to ensure safe working around transmitting antennas. If you enjoyed this article, please subscribe to our newsletter or download our free Introduction to RF below.
Image source: IXUS