Soaking up the waves. RF might hurt you.
 I'll
never forget one of the first NAB workshops on the hazards of RFR.
It was at the 1986 NAB show in Dallas. The venerable Denver consultant
Vir James proclaimed, "I've been around RF all my life and
can't get enough of it. I love the stuff." Other than a few
RF burns over the years, he didn't think his health had been diminished
by it one bit. Vir lived to a ripe old age.
In those days, he and many other engineers weren't so sure the
newly proposed RFR regulations were completely necessary or appropriate.
But the new FCC laws were going on the books designed to protect
humans from over-exposure. We all had to understand and abide by
them.
The great radiation debate
Debate over the term radio-frequency radiation, or RFR, lingers.
That was the FCC's chosen descriptive phrase when the first OST
Bulletin #65 was released in 1985. It's not really radiation in
the same way most folks understand the term. Ever since Hiroshima,
the public associates radiation with the nuclear fission ionizing
variety. Radio waves are, of course, non-ionizing, meaning the basic
molecular structure of anything subjected to them remains unchanged.
RF energy really is a lower frequency invisible form of sunlight.
I'd prefer the term RFE over RFR. It would certainly help to calm
down fear-mongering NIMBYs living near existing or proposed antenna
towers. In its revised OST 65, released in 1997, the FCC started
using the term "radio-frequency electromagnetic fields"
in place of RFR. IMHO, RFE is shorter, more appropriate and easier
for almost anyone to understand.
The FCC adopted rules regarding RF exposure, based on the National
Environmental Policy Act of 1969 (NEPA) that required federal agencies
to evaluate the effects of their actions on the human environment.
The NCRP, IEEE and ANSI established the limits adopted by the FCC
based on specific absorption rates of energy that produce elevated
temperatures and possible detrimental biological effects on human
tissue.
RF the smoking gun?
Other than this obvious effect of tissue heating, we still don't
know what the long-term implications or risks to human health really
are regarding absorption of broadcast RF. Like any other abnormal
stimulus or agent subjected to the human body, RF exposure may induce
different consequences from one human to another.
The rules and guidelines contained in OST 65 really are based on
the assumption there might be adverse health risks associated with
excessive exposure. The 1997 NAB publication on FCC RF radiation
regulation compliance that includes OST 65 clearly states, "Although
much scientific research has been done in the area of human exposure
to RF radiation, as of this writing no conclusive connection between
exposure to relatively low levels of RF radiation and health effects
in human beings has been established. ... Neither the FCC nor any
other arm of the federal government has determined that broadcast
antenna emissions at levels normally encountered by workers or the
public pose a present public health hazard. It is important to remember
that the regulations have been adopted as preventative and precautionary
measures."
It's rather curious the government has gone to such great lengths
to protect the public from possible adverse health effects of RF
energy but almost nothing in the area of consuming junk food. Ingesting
high levels of sugar and fat certainly pose a much larger health
risk for everyone. At least they have determined that smoking tobacco
is hazardous to one's health and have become rather proactive in
controlling its use. But I digress.
Don't get burned
Microwave ovens heat up food really well with a high-power magnetron
beam of 2 GHz energy. Certainly human exposure to near-field microwaves
can induce problems, especially eye damage if you look right at
them. Not much different than watching an eclipse of the sun.
I recall climbing an FM tower back in the 1970s and feeling the
heat coming off a 10 kW FM bay within a few feet. Not a very efficient
space heater, but I would have absorbed a lot more heat and probable
tissue damage by sunbathing on the beach.
If you've talked with any old-timer tower climbers about RF, many
will admit to years of probable over-exposure. A few even laugh
at the stringent standards that are now law. While most have weathered
their past indiscretions with no ill effects, a few have died of
cancer and their widows have filed lawsuits. But was RF the real
culprit? It's impossible to know for sure.
Reasoning that it's better to be safe than sorry, most responsible
tower firms abide by the rules and now require their workers to
carry RF sensing devices to warn of hot spots. Sometimes they can
be a bit too sensitive. We've heard at least one story of a fussy
tower crew delaying work with nervous sensors warning of RF that
turned out to be well below safety margins. And then there are a
few of those small renegade tower outfits that are willing to ignore
safe limits just to get the work done and make the money. Both sides
need to be vigilant when working around RF.
Trouble in Caly
Recently, the industry has learned of two RF exposure infractions
by broadcasters in California that have achieved high profile by
provoking FCC investigations. Thanks to the CGC Communicator (www.bext.com/_CGC)
for many of the details we've gleaned on this.
Although various local engineers familiar with the stories also
have offered slightly different accounts of what occurred, I believe
the following essentially sums up what did happen:
First, the Sunset Ridge incident involves a TV station that allegedly
turned up its transmitter power to full throttle when tower workers
were on the tower in proximity of the antenna. Apparently an out-of-state
TV network director of engineering ordered the local station to
resume full-power operations. It is not known for certain if that
individual realized there were tower workers being exposed to high
RF energy by his decision.
Whether the workers were exposed to dangerous RF levels is unknown.
Personal RF monitors worn by the workers alerted them. Apparently,
they were able to climb out of the hot area before the transmitter
was again shut down or before time-averaged extended exposure was
exceeded. The FCC is investigating and may issue citations to the
local station. Heads could roll on this one.
Miscalculation gone awry
The other incident involves a TV station installing a new DTV antenna
on Mt. Wilson. This site is perhaps the busiest and largest antenna
farm in the nation and is home for most L.A.-area FM and TV station
transmission facilities. Getting all nearby stations to co-operate
with necessary power reductions to allow such work is understandably
difficult and time consuming.
The TV CE notified and secured the co-operation of all nearby stations
he calculated would present a problem for tower workers doing the
work. But RF safety monitors started beeping as workers climbed
the tower. He apparently had forgotten the RF contribution by a
nearby FM station. The CE of that station was called, with no prior
notice, and was asked to reduce power by 20 percent so the work
could proceed. He complied and work progressed without further incident
that day.
The next day, the FM station was again asked to reduce power. This
time their corporate engineer initially declined to co-operate,
apparently citing loss of coverage during morning drive and inadequate
advance notice for non-emergency work that should have been pre-scheduled
outside of drive time. The TV CE understandably was not happy, with
an expensive tower crew waiting to go to work and all other stations
onboard.
A big can of worms
After a few hours of heated discussions and delays, including having
to persuade the station's management that a power reduction of only
20 percent would not affect meaningful coverage, the FM station
did lower power and work proceeded. However the local FCC field
office was made aware of these proceedings, spilling a can of worms
all over Mt. Wilson. For the next several days, a cadre of FCC officials
visited the site to do a thorough inspection and RF compliance evaluation.
All of the stations involved in the vicinity of the DTV project
were required to shut down transmissions one by one for brief periods
to allow for actual RF density measurements. Perhaps the most obvious
infraction was an access gate left open and unlocked that essentially
allowed public access to the area. The reluctant FM station may
not have violated any actual rule. Those responsible for leaving
the gate open and unlocked probably did.
There are hundreds of mountaintop FM and TV tower sites all over
the country. The FCC recognizes the public does not normally frequent
them. But just like sites in populated neighborhoods, the main thing
that prevents easy public access is an effective locked gate at
the access road and a perimeter fence if feasible. Warning signs
also are necessary but are not enough by themselves.
Setting the example
A number of Mount Wilson station CEs expect that some citations
and possible fines will be issued. As of this writing, the FCC still
is analyzing its measured data and the facts involving the incident.
The commission apparently wants to set an example and raise awareness
with this episode and sees RF compliance as a hot-button issue,
along with EAS.
The FCC's rules on RF exposure and compliance have been on the
books for 18 years. Every station must certify that its antenna
installation complies with the rules at license renewal time, including
provisions for power reduction to protect workers. Multi-user sites
have had to cooperate on a mutual basis to ensure that tower workers
as well as the public are protected from any over-exposure.
Most such sites have drafted written procedures that spell out
how much power reduction is required for workers to safely access
mapped areas of the tower structure to perform work or maintenance.
Mt. Wilson users now are carefully reviewing their plan and likely
will update it to cover any contingency.
Certainly reliable communications need to be established and maintained
between tower crews in the air and engineers on the ground when
tower work is underway. Now that personal RF monitors are widely
available and in use, there
should be little chance or reason any tower worker is over-exposed
to high levels of RF. Every CE employing tower workers on his site
should insist on their use. This is just good inexpensive insurance.
The keys to preventing problems in this arena are careful planning
and execution, with everyone involved paying close attention to
established rules, procedures and common sense.
Can't we all just get along?
It would appear that the Mt. Wilson boondoggle could have been
prevented and kept off the FCC's radar screen had a little more
mutual understanding and co-operative spirit been employed. Scheduling
non-emergency tower work during morning drive in a major market
is usually never done unless there are special extenuating circumstances.
Coordinating with those stations involved with as much advance notice
as possible for non-emergency work is common courtesy.
On the other hand, a request to reduce power by only 20 percent
is almost no reduction at all - a little over 1 dB in lost field
strength. Usually, such reductions are 50 or even 90 percent. When
work is underway, with men on the tower and other stations running
at reduced power, common sense dictates that co-operating to get
the job done would have been the wiser choice, one that also would
pay off in the future. Every station that is part of an antenna
farm complex eventually will need to deal with its own problems
or projects that require the co-operation of its neighbors.
When you need a favor, everybody remembers who cooperated last
time and who didn't. Of all the rules we might want to impose on
tower work operations, perhaps the golden rule is the one that matters
the most.
Guy Wire is the pseudonym for a veteran broadcast engineer with major-market radio credentials. His opinions are his own and do not necessarily reflect those of Radio World. RW welcomes other points of view.
|
