Are ham radio antennas dangerous

Do you ever work on rooftops or perform renovation work on the outside of buildings? If so, you may be exposed to an invisible hazard without even realizing it. That hazard is radiofrequency (RF) radiation, and it’s used to transmit wireless information, usually through antennas.

• RF radiation is hard to recognize – it is invisible, odorless and tasteless
• By the time workers feel symptoms (e.g., overheating, reddening of the skin) they are already overexposed
• Levels can be low at the start of work and spike without warning
• RF radiation may interfere with medical devices (e.g., pacemakers) and concerns have been raised about possible non-thermal effects (e.g., nerve damage and psychological injuries)

Rooftop and building-mounted antennas can expose nearby workers to high levels of RF radiation. Many antennas are hidden or camouflaged – a practice known as “stealthing.” Knowing this, what can employers and workers in the construction industry do to protect themselves?

Protecting Workers from Overexposure

There are currently no regulations on RF exposure, though a number of organizations have issued recommended exposure levels and best practices. Exposure levels vary based on many factors, but at a minimum, workers should stay six feet away from a single antenna or ten feet away from a group of antennas. Employers should also make sure nearby antennas or those on adjacent buildings are not pointed directly at the work area.

Employers must ensure workers potentially exposed to RF radiation have a safe and healthy workplace. For this reason, employers who do this kind of work should have a comprehensive plan for how to prevent overexposures. Listed below are key elements of such a plan adapted from the Institute of Electrical and Electronics Engineers’ Recommended Practice for Radio Frequency Safety Programs, 3 kHz – 300 GHz (C95.7 – 2014).

• Control hazards using engineering controls (e.g., physical barriers such as railings or shielding the source of radiation) and administrative controls (e.g., signage, safe work practices, source power control)
• Identify hazards through exposure assessments or an RF source inventory provided by a building owner
• Train workers to be aware of the hazard, including RF exposure limits and incidence response
• Maintain administrative elements including a written policy, medical surveillance program and safety committee with worker involvement
• Provide and ensure the proper use of personal protective equipment (PPE) as a last resort

As telecommunications equipment becomes more widespread and more powerful, potential exposures to RF radiation will continue to rise. But careful planning by both employers and workers can effectively reduce exposure to this invisible hazard.

[Travis Parsons is the LHSFNA’s Senior Safety & Health Specialist.]

There are two safety considerations to bear in mind when setting up a radio shack – electrical safety and RF safety.

You will no doubt be using radio equipment that is mains powered, and you will probably use 12 V supplies that can supply up to 25 A or more. Mains electricity can kill you and that innocuous looking power supply could easily cause a fire if a short circuit occurs and you don’t have adequate safety precautions, such as a fuse.

Also, you will be producing radio frequency (RF) energy, which should be treated with respect.

Let’s deal with each of these in turn.

Electrical safety

The wiring for your shack should ideally be controlled by one master switch and everyone in the house should know where it is. A fire extinguisher, suitable for use on electrical fires, is also a good investment.

All wires carrying power around your station should of the proper size and quality for the job. Also, all equipment should be connected to a good earth.

When working on equipment you should, if possible, ensure that it is switched off and unplugged. Any capacitors should be discharged as they can store charge for a considerable time.

If you must work on live equipment only do so if you know what you are doing. Also, keep one hand in your pocket at all times and all metal jewellery should also be removed. Avoid bodily contact with any earthed object to prevent you becoming the return path for any voltage source to ground.

If possible do not work on equipment when alone and always make sure that you have the correct tools for the job.

RF Safety

Radio Amateurs should be concerned about two aspects of RF safety when planning a station and its associated antennas.

Physical contact with antennas and parts of the station, which may be RF ‘hot’ and where there is a risk of RF burn or electric shock, must be a primary consideration.

This might include feeders to the antennas, or ungrounded metallic objects within the station or nearby.

Always arrange your antennas and feedlines so that they cannot be touched. This may mean re-routing them or putting them out of harm’s reach.

The second aspect is safety near the antennas in the so-called “near field”.

This the region where the distance from a radiating antenna is less than the wavelength of the radiated energy.

This implies that on the lower HF bands, say on 160 metres (Top Band), the near field could extend a considerable distance from the antenna.

However, in practice such an antenna would also be physically large, and would result in the incident power being widely distributed over a large area. For resonant dipoles there is a significant magnetic field near the feed, and a high E field near the antenna tips – both of these need to be considered as a safety consideration.

Every radio amateur should always ensure that persons in or near the station are not within the near-field safety zone recommendation of the antenna when transmitting.

But what is that zone? This is complex and you need to read the document “RF Safety and the Radio Amateur” mentioned above.

If you read nothing else, there is a rough rule of thumb.

For example, if you use a dipole, and 400 Watts, take the frequency in MHz, and use that spacing in feet (ft). That is, on 14 MHz a spacing of 14 ft is required as a safety distance. Or … If you use a beam with a gain of 9dB, and a transmit power of 100W, take the frequency in MHz, and use that spacing.

As you can see the higher you go in frequency the further you must keep away from transmitting antennas.

Other pages in this section – Setting up your shack:

Part 3 on Safety

Safety is an important topic in ham radio.  There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Part 1 on general electrical hazards and Part 2 on contact RF hazards were posted previously.  This post will address indirect RF hazards.  In case you are not familiar with the specifics of RF energy, refer to our post on the subject.

Here we are concerned about non-contact RF energy.  A long and involved topic (sorry about that) but full of useful detail.

While it involves radiation, RF energy radiates at lower wavelengths where it is least hazardous.

From the electromagnetic spectrum diagram above we see that radio waves are on the low end of energy levels.  As the frequency increases (wavelengths decrease) the energy in electron volts increases exponentially.  Energy above 250eV (or so) is ionizing, which in addition to radiation burns can cause cell damage and mutations, leading to cancer and other maladies, as would radioactive material.

Fortunately for hams, all radio frequencies are well below the ionizing radiation energy levels.

Ham radio operators are radio  active, not radioactive. 🙂

Because RF energy has this radiated exposure risk, rules and regulations have arisen to protect people from such hazards.  In the USA this is done at the federal level by both the FCC (radio communications) and OSHA (occupational).  There are also guidelines for RF radiation published by the ARRL and the IEEE.  Internationally, most countries apart from the US have similar guidelines, as does the World Health Organization (WHO).  References to some of these are given at the end of this presentation.

Specific to US radio amateurs, the FCC instituted RF field exposure limits called Maximum Permissible Exposure (MPE).

Frequency is a factor in MPE.  Due to human physiology, tissue heats more at certain frequencies than others based on the specific absorption rate (SAR).

Note the difference in a controlled environment vs an uncontrolled one.

In a Controlled Environment you know where people are standing in relation to your antenna and you can do something about it.  Higher power density is allowed because you can make adjustments if needed.  6 minute average exposure.

In an Uncontrolled Environment you have no control of people near your antenna.  Lower power density is allowed because you cannot control or adjust the exposure of people.  30 minute average exposure.

So we see that frequency is a factor in RF exposure.  Intuitively we also know that power level is also a factor; more power will heat tissue faster; less power not so much.  RF power also affects the body by the inverse square of the distance (geometric dilution) so proximity to (or rather, distance from) the radiator is yet another factor, as is the radiation pattern.

Proximity to an amateur radio antenna of any radiation pattern is the single most influential factor.  If your antenna is dozens or hundreds of feet away from the control operator position, it’s likely that you’ll be perfectly safe.

Conversely,  sitting right next to a directional antenna and using high transmit power on VHF bands is the most hazardous scenario.

Duty cycle is also a significant factor in MPE because it determines exposure over time (critical long-term exposure), unlike immediate or instantaneous levels which are not as critical to biological RF absorption.  It make sense that a transmission with a low duty cycle presents less exposure than a high duty cycle one.

Duty cycle is how long a transmitter is active in a given period.  Basically how much time you are transmitting vs receiving, measured in percent (%).

To help relate mode to duty cycle, refer to the chart below.  While generalized, it gives a basic idea for comparison of commonly-used mode duty cycle.

A higher duty cycle means higher average power density and exposure but it’s the average that counts; the MPE limit are based on average exposure.  So with a 50% duty cycle you can double the power density and remain in the safe limits of MPE.

In summary, to reduce RF exposure there are five things you can do:

• Relocate or reorient antennas
• Raise the antenna
• Reduce antenna gain
• Reduce RF power output
• Change to a lower duty cycle mode

All US amateur radio stations must comply with the MPE limits, regardless of power, operating mode or station configuration. This requires an exposure evaluation.

There are three acceptable methods, all listed in the Technician license exam question:

The first is done with an online calculator referenced by OET Bulletin 65 and is fast and simple (recommended).  Computer modeling is also possible if you have the software and the knowledge and skills to use it (somewhat difficult).  Actual measurement of your RF fields requires calibrated equipment which is unavailable to most hams (expensive, difficult).  Obviously we recommend the online calculator.

Fortunately the FCC presumes that certain stations are safe without an evaluation. Those are:

• Amateur stations using a transmitter power of less than 50 W PEP at the transmitter output terminal.
• Mobile or portable stations using a transmitter with push-to-talk control.

This means that if you have a transmitter with less than 50W output, or if it has only a microphone for voice mode, an RF exposure evaluation is not required.  This includes most VHF/UHF mobile FM transceivers.

Once you have evaluated your station and are in compliance you should re-evaluate whenever anything related to RF emissions is added or changed (antenna, radio, new frequencies/mode, etc.)

RF exposure references

Ham radio school topic, RF Exposure

Ham radio school topic, Evaluating Your Station

US Federal Communications Commission (FCC) RF Safety FAQ

FCC Overview of RF Exposure Concepts and Requirements (includes detail on controlled vs uncontrolled environments)

ARRL topic, RF Radiation and Electromagnetic Field Safety

US Department of Labor OSHA topic,  Radiofrequency and Microwave Radiation

World Health Organization topic, Electromagnetic fields

IEEE Standards relating to RF radiation