Chapter 9
Safety
Chapter 9
Safety
Today’s agenda
• Working safely with electricity
• Safety grounding
• Lightning protection
• RF exposure rules
• Evaluating your station
• Reducing exposure to RF
Chapter 9
Safety
Today’s agenda (Continued)
• Safely installing antennas
• Working on and around towers
Chapter 9
Safety
There is nothing particularly risky about working with
electricity, antennas, or climbing towers.
Compared to many activities, amateur radio is one of the
safest hobbies because most hams educate themselves
about safety and follow some simple rules and here’s where
it gets dangerous --- they use “common sense” and
unfortunately, “common sense” is not distributed equally
across the gene pool.
Chapter 9
Electrical Safety
Working safely with electricity mostly means avoiding
contact with it.
Compared to many activities, amateur radio is one of the
safest hobbies because most hams educate themselves
about safety and follow some simple rules.
Sometimes a little common sense goes a long way.
Chapter 9
Electrical Safety
Electrical Injuries
Electrical hazards produce two types of injury:
• Shocks and
• Burns
Whenever electricity flows through any part of your body
both can occur.
Shocks and burns can be caused by ac or dc and result
from current flow through the body.
Chapter 9
Electrical Safety
Electrical Injuries
Effects of Electric Current in the Human Body
Current
Reaction
Below 1 milliampere
Generally not perceptible
1 milliampere
Faint tingle
5 milliamperes
Slight shock; not painful but
disturbing; Average person
cannot let go
6-25 milliamperes (Women) Painful shock, loss of muscular
9-30 milliamperes (Men)
control; “can’t let go” range.
Chapter 9
Electrical Safety
Electrical Injuries
Effects of Electric Current in the Human Body
50-150 milliamperes
Extreme pain; respiratory arrest;
severe muscular contractions; death
is possible.
1000-4300 milliamperes
Heart pumping ceases; muscular
contraction and nerve damage; death
likely.
10,000 milliamperes
Cardiac arrest; severe burns; death
probable
Chapter 9
Electrical Safety
Electrical Injuries
The most dangerous currents are those that flow through
the heart:
• Hand-to-hand
• Hand-to-foot
A current of 100 mA or more can disrupt normal heart
rhythm.
Voltages as low as 30 volts can cause enough current flow
to be dangerous.
Chapter 9
Electrical Safety
Electrical Injuries
Electrical hazards produce two types of injury:
• Shocks and
• Burns
Whenever electricity flows through any part of your body
both can occur.
Shocks and burns can be caused by ac or dc and result
from current flow through the body.
Chapter 9
Electrical Safety
Avoiding Electrical Hazards
Never work on “live” equipment unless it is absolutely
necessary (e.g., Troubleshooting or testing).
Never assume equipment is off or de-energized. Check with
a meter or tester first.
Capacitors in a power supply can store hazardous voltage
after the charging circuit is turned off.
• Test with a meter
• Use a grounding stick to shunt the charge to ground.
Chapter 9
Electrical Safety
Avoiding Electrical Hazards
If you have to work on “live” equipment follow these
guidelines:
• Keep one hand in your pocket when probing or testing
energized equipment.
• Never bypass a safety interlock unless specifically
instructed to do so.
• Remove your jewelry when working on electronics.
Chapter 9
Electrical Safety
Response to Electrical Injury
If you or someone receives an electrical shock…
Turn off the power – don’t touch the person while they are in
contact with electricity or you will be the next victim.
Install a clearly-labeled master ON/OFF switch for the circuit
to your ham shack. Show your family how to turn off power
at the switch AND at the circuit breaker box.
You and your family should consider learning CPR and first
aid for electrical injuries.
Chapter 9
Electrical Safety
AC Safety Grounding
Most ham stations DO NOT require new wiring and can
operate safely when powered from your home’s ac wiring.
You just have to follow some simple guidelines:
• Use three-wire power cords that connect the chassis
of your equipment to the ac safety ground.
• Use Ground Fault Circuit Interrupter (GFCI) circuit
breakers.
• Use a circuit tester to verify proper wiring
Chapter 9
Electrical Safety
AC Safety Grounding
• NEVER replace a fuse or circuit breaker with one of a
larger size.
• Don’t overload single outlets.
• If new wiring is required, hire an electrician do it or at
least inspect your work.
• Be sure to follow the “Hot-Black” (occasionally Red),
“Neutral-White”, “Ground-Green” (or bare wire) wiring
standard
Chapter 9
Electrical Safety
AC Safety Grounding
• Use cable and wire sufficiently rated for the expected
current load.
• Use the proper size fuses and circuit breakers.
• If you build your own equipment, always install a fuse or
circuit breaker IN SERIES with the ac “hot” conductor.
Chapter 9
Electrical Safety
RF Burns
RF burns result from contact with a “hot spot” – a location
where high RF voltage is present on the outside of a
connector, cable or equipment enclosure. The RF voltage
creates currents in the skin at the point of contact.
Can be painful but don’t do much damage
Using a common ground all of the radio equipment at the
same RF voltage thereby minimizing “hot spots” and the
possibility of a burn.
Chapter 9
Electrical Safety
Lightning
Lightning strikes amateur towers and antennas NO MORE
frequently than tall trees or other structures.
However, common sense must prevail and there are some
things you should do regardless of where you live.
• Ground all towers, masts and antenna mounts
• Ground at the base or if roof-mounted, use a large
diameter wire to a ground rod.
• Ground connections should be as short as possible
and avoid sharp bends.
Chapter 9
Electrical Safety
Lightning
• When lightning is anticipated, disconnect all cables
outside the house.
• Unplug equipment power cords inside the house.
• Operating during a thunderstorm is never a good idea.
• A nearby strike can create a voltage surge of
thousands of volts in a power line or phone line.
Chapter 9
RF Exposure
After many studies done at power line frequencies (50 and
60 Hz) and radio frequencies of RF (shortwave, including
amateur frequencies and mobile phone), NO LINK has been
established between low-level electromagnetic radiation
and health risks.
At the relatively low frequencies used by radio amateurs, RF
energy is “non-ionizing radiation”.
Chapter 9
RF Exposure
Despite a lack of evidence that radio frequencies (RF) pose
a health risk, it’s a good idea to avoid unnecessary
exposure to high levels of RF.
The FCC has set limits on the “Maximum Permissible
Exposure” (MPE) from radio transmitters of any sort.
Hams are required to evaluate their stations to see if their
operation has the potential to exceed MPE levels.
RF energy can ONLY cause injury to the human body IF the
combination of frequency and power causes excessive
energy to be absorbed.
Chapter 9
RF Exposure
There are two techniques to ensure that humans are not
exposed to high-strength fields of RF energy:
• Prevent access to locations where strong fields are
present.
• Make sure strong fields are not created in or directed
towards areas where people might be present.
RF burns can be eliminated by proper grounding techniques
or by preventing access to an antenna.
Chapter 9
RF Exposure
When the human body absorbs RF energy, heating occurs.
• RF energy causes the molecules in the body to vibrate
at the same frequency.
• The energy of the vibration is dissipated as heat.
Absorption of RF energy varies with the frequency because
the body absorbs more RF energy at some frequencies than
others. The human body absorbs more RF energy at VHF
frequencies than any other part of the RF spectrum.
Chapter 9
RF Exposure
The intensity of an RF field is called “power density”.
• Measured in several ways
• Most common is milliwatts per square centimeters
(mW/cm2)
Power density is highest near antennas and in the directions
where antennas have the most gain. It’s also very high
inside transmitting equipment.
Increasing transmitter power increases power density
everywhere around an antenna.
Chapter 9
RF Exposure
The further away you are from an antenna the lower the
power density in proportion to the square of the distance
from the antenna.
At twice the distance from the antenna, power density is
divided by four.
Controlling the power and distance, forms the basis for
amateur RF safety.
Chapter 9
RF Exposure
The FCC has established safe levels of RF exposure –
Maximum Permissible Exposure (MPE) levels.
MPE and absorption rates vary with frequency.
Absorption rates vary with the size of the body or body part
and is highest where the body is naturally resonant.
The full body is resonant at about 35 MHz if grounded and
about 70 MHz if not grounded.
Body parts are resonant at higher frequencies (e.g., an
adult’s head is resonant at about 400 MHz).
Chapter 9
RF Exposure
Above and below the ranges of highest absorption, the
body less and less to the RF energy.
The highest absorption rates are above the HF portion of
the RF spectrum – 30 to 1500 MHz.
The highest RF energy is at VHF frequencies (30-300 MHz)
regardless of whether it is a “controlled” or “uncontrolled”
environment.
Chapter 9
RF Exposure
In a “controlled” environment people are aware of the their
exposure and can take the necessary steps to minimize it:
• Wear hats and blankets made of aluminum foil
• Sit in a lead-lined room below ground
• Attach grounding wires to your big toes
On a serious note, the FCC has determined that the
“controlled” environment generally applies to amateur
operators, their family members and their guests and is
limited to your home and property.
Chapter 9
RF Exposure
People in “uncontrolled” environments are not aware of
their exposure – areas open to the general public and your
neighbor’s property – and their risk of exposure is generally
less than in “controlled” environments.
Note: Even in “uncontrolled” environments, wearing
aluminum foil hats is strongly recommended.
Chapter 9
RF Exposure
Exposure limits are based on averages rather than peak
exposure.
• The averaging period for controlled environments is 6
minutes.
• The averaging period for uncontrolled environments is
30 minutes
The difference in averaging periods reflects the difference in
how long people are expected to be present and exposed.
Chapter 9
RF Exposure
Duty cycle is the ratio of the transmitted signal’s on-the-air
time to the total operating time during the measurement
period. The maximum is 100%
For most amateur contacts, the transmitter is keyed no
more than 50% of the time and usually much less which in
turn lowers the “duty cycle” of the emissions.
Because duty cycle affects the average power level of
transmissions, it must be considered when evaluating
exposure.
Chapter 9
RF Exposure
Antenna Gain is the last piece of the puzzle that we must
consider.
Beam antennas focus radiated power toward one direction
which results in increased gain. Therefore, gain increases
your average power in the preferred direction.
There are four factors that affect RF exposure;
1.
2.
3.
4.
Transmitter power
Frequency
Distance to the antenna
Radiation pattern of the antenna
Chapter 9
RF Exposure
With the exception of mobile and hand held transceivers,
the FCC requires all fixed stations be evaluated for RF
exposure.
The use of special equipment and computer modeling are
acceptable but are too expensive or too much effort is
required.
Most evaluations use the techniques outlined in the FCC’s
Office of Engineering Technology (OET) Bulletin 65.
• Uses tables and simple formulas to determine if your
station has the potential of causing an exposure hazard.
Chapter 9
RF Exposure
Once you’ve done an evaluation you do not need to do
another unless you change equipment that affects the
average output power (e.g. added an amplifier or increased
antenna gain). You’ll also need to reevaluate if you add a
new frequency band.
If your transmitted power (PEP) is less than the levels
indicated below on the frequencies you operate, then no
evaluation is required. The FCC has determined that the
risk of exposure from those levels is too small to create an
exposure risk:
Chapter 9
RF Exposure
Power Thresholds for RF Exposure Evaluation
Band
Watts
Band
Watts
Band
Watts
160 m
500
15 m
100
70 cm
70
80 m
500
12 m
75
33 cm
150
40 m
500
10 m
50
23 cm
200
30 m
425
6m
50
13 cm
250
20 m
225
2m
50
SHF (all bands)
250
17 m
125
1.25 m
50
SHF (all bands)
250
If you need to do an evaluation, you can use on-line exposure
calculators and pre-calculated tables. You’ll need to know the
frequency and power level, distance from the antenna and the
antenna’s radiation pattern.
Chapter 9
RF Exposure
If you need to do an evaluation, you can use on-line
exposure calculators and pre-calculated tables.
Whichever method used, you’ll need to know the frequency
and power level, distance from the antenna and the
antenna’s radiation pattern.
Conduct the evaluation for each
frequency band and antenna used on that band.
Chapter 9
RF Exposure
So what do you do if you find a potential hazard?
You could issue everyone a hat made of aluminum foil or…
• Locate antennas away from where people can get close
to them – you don’t want anyone to be able to touch the
antenna.
• Raise the antenna – it usually improves your signal as
well as being a good safety practice.
• Avoid aiming a beam antenna where people are likely
to be.
Chapter 9
RF Exposure
• Use a lower gain antenna.
• Reduce your transmitter power.
• Limit or reduce the average power of your
transmissions.
• Transmit for shorter periods
• Use a mode with a lower duty cycle
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
When installing a radio in your vehicle you want to preserve
the safety you and your passengers:
• Secure all equipment inside the vehicle
• If possible, use “control heads” (detachable front
panels)
• Don’t install the radio where it diverts your attention
from driving or can block your view.
• Don’t operate in heavy traffic
• Pull over to make complicated adjustment
• Know the traffic laws in your state
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
Before you start installing a tower or an antenna on your
property, check with your home owner’s association and
also check any local zoning codes to ensure that it’s OK.
If your tower exceeds 200 feet or you’re near an airport
you’ll need to check with the FCC and the FAA.
Place all antennas and feed lines clear of power lines
including the service drop to your home.
Ensure you have at least 10 feet of clearance beyond your
mast or tower height from the nearest power line.
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
Never attach an antenna or guy wire to a utility pole since a
mechanical failure could result in contact with high-voltage
wires.
Follow your local electrical code when grounding antennas
and support systems.
Towers should be grounded with separate 8-foot long
ground rods for each tower leg, bonded to the tower and to
each other.
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
Most antennas work better when installed as high as is
practical and that usually means installing a tower or some
sort.
When working on a tower or as part of the ground crew,
safety is absolutely critical.
• Each member of the crew should wear hard hats,
goggles or safety goggles, and heavy gloves.
• Use sun screen lotion
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
• If you’re the “climber” use an approved climbing
harness – DO NOT use a “lineman’s belt” – and work
boots to protect the arches of your feet.
• Inspect all tower guying and support hardware. Repair
or tighten before you climb.
• Crank-up towers must be fully nested in the retracted
position and blocked. Never climb a crank-up tower
supported only by its support cable.
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
• Double-check all climbing belts and lanyards. Make
sure all clips and carabiners work smoothly and do not
stick in the open or closed position.
• Make sure all ropes and load-bearing hardware are in
good condition.
• Use a gin pole (a temporary mast that is attached to
the tower) to hoist stuff (e.g., tools, parts, tower
sections, antenna, etc.) up the tower.
Chapter 9
Mechanical Safety
ALWAYS FOLLOW THE MANUFACTURER’S DIRECTIONS!
• Double-check the latest weather reports.
• Visit the bathroom before you climb the tower. Your
ground crew will thank you.
• Avoid climbing alone whenever possible because it’s
never safe.
• Make sure all power to the tower is turned off.
• Stay clear of the base of the tower unless you need to
be there and never remove your hard hat until the
climber is on the ground.
Chapter 9
Mechanical Safety
The End