By Victoria W. Kipp
Site Management & Technology (SMT) magazine, Dec 1, 2002
A tower technician 20 years ago would climb to his working height and then attach a safety belt to the tower. That was considered an acceptable way to operate. Times have changed, and that practice is no longer acceptable.
Safety Guidelines
A daily job-site tailgate meeting is a requirement for safety. Safety training should be conducted on every job, every day. At daily site meetings, tower crews discuss fall hazards, RF exposure and environmental risks, and then take appropriate action.
Some examples of tower safety rules are:
• Tower technicians should be 100% tied-off when ascending, descending or transitioning on a tower.
• Workers and materials should never be hoisted together.
• No more than two workers may be hoisted at a time.
• A tag line should be used to prevent workers from contacting the tower during hoisting.
• A cat head (capstan winch) may not be free-spooled or used to lift workers.
• Hoist or winch operators are to remain at the controls at all times when workers are on the hoist line.
These rules help prevent avoidable work site injuries.
Fall Protection
Because the “100% attachment” initiative began in the mid-1990s, fall protection has become a focal issue for tower technicians. Before ascending a tower, technicians are outfitted with a full-body climbing harness, lanyards, hard hat and leather gloves (Figure 1).
The full-body harness wraps around the technician’s waist, shoulders and legs. Lanyards and other fall arrest connection devices connect to a D-ring in the center of the back of the harness. Optional side, front and shoulder D-rings provide connection points for work positioning and retrieval from confined spaces.
If a fall occurs, the full-body harness distributes the impact force throughout the trunk of the body. The pelvis and shoulders absorb part of the shock, reducing the force to the abdominal region. A full-body harness is designed to absorb a maximum arrest force of 1,800 pounds.
A connection device attaches the harness to the final tie-off point. A single lanyard or a combination of lanyards, lifelines, worklines, rope grabs, tie-off straps and carabiners can make the connection.
Fall protection lanyards are constructed of steel, nylon rope, or nylon or Dacron webbing. The lanyard material type, free-fall distance and the weight of the worker determine the arresting force from a fall. Using a shock-absorbing lanyard or a higher tie-off point can reduce impact force. Some lanyards are shock-absorbent to reduce the potential fall arrest force. Because a lanyard used for fall protection is limited to allow a maximum free fall of six feet, most lanyards are no longer than six feet.
The place where a lanyard or lifeline attaches to a tower structural member is the tie-off point. The structural support must have a 5,400-pound capacity for each worker tying off. The tie-off point must always be at or above the D-ring of the worker’s harness to minimize free fall. To ensure that a worker will not strike a lower level during a fall, the following formula is followed to determine the tie-off point: worker height + lanyard length + elongation factor of 3.5 feet 5 minimum distance above the next lower level that the tie-off point must be placed.
A lifeline used in combination with a rope grab adds flexibility to a fall arrest system by allowing the worker to move along the length of the line rather than having to disconnect and find a new tie-off point. The system allows the worker to move as long as tension is slack on the lifeline. If the worker falls, the tension on the rope grab instantly triggers an internal mechanism to arrest a fall.
Safety equipment vendors stress that any equipment that has been exposed to a fall must be taken out of service and not used again for fall protection. The Occupational Safety and Health Administration requires that all fall arrest equipment be inspected prior to its use. Aging, mechanical wear and ultraviolet ray degradation can weaken safety equipment over time. Inspection includes looking for frays or broken strands in lanyards, belts, and lifelines, and for oxidation or distortion of any metal connection devices.
Risks Remain
Although tower technicians can take comfort in the fact that they practice 100% attachment while working on a tower, they don’t have that protection when they must climb onto an antenna. For example, the tower technician may find the tower is entirely enclosed until he reaches the antenna. When servicing the antenna, the technician may have to climb up another 100 feet. He can’t tie on to the antenna and is exposed to the risk of falling. There are no easy answers for dealing with this risk. The tower industry is pushing for antenna designers to engineer a safety system as an integral part of Pylon antennas.
Hot tower climbing
Before a technician begins ascending, be sure that the appropriate transmitters have been deactivated and locked out. This precaution prevents someone from accidentally turning on the transmitters while a technician is performing maintenance. With so many antennas sharing one tower, it becomes more difficult to confirm that all of the transmitters are deactivated. It may not be possible to have the collocated antennas that aren’t being serviced powered down. These other antennas may remain on while operating at reduced power.
RF MPE Rule
Effective Sept. 1, 2000, the FCC required nearly every licensed station to comply with human RF exposure standards. The goal of this rule is to limit human exposure to RF energy. Although X-rays or nuclear energy cause ionizing radiation that can permanently change the molecular structure of a cell, RF energy is non-ionizing and is believed to heat cells without causing molecular change. RF energy does not do permanent damage to cells, as long as the amount of heating is limited to safe levels.
The FCC has specified safe levels for RF exposure based on:
• The intensity of the RF field.
• The wavelength of the energy (the body is most susceptible to heating from 30MHz to 300MHz).
• The duration of the exposure.
If RF levels exceed the FCC threshold in any of these areas, then FCC time limits apply. The FCC rules do not limit the maximum levels of RF encountered, but rather the maximum time that a human can be in the field.
As for the RF field, the FCC rules recognize two types of areas.
An accessible, uncontrolled area is one where the public may be exposed to RF. It also is where people may be exposed in the course of their employment without being fully aware of the exposure or without being in a position to exercise control over it.
An occupational, controlled area is one where people are exposed as a result of their occupation. People are allowed into this area only if they have been made fully aware of the exposure and if they can exercise control over their exposure.
The FCC limits the maximum permissible exposure to 30 minutes for a controlled area and six minutes for an uncontrolled area.
RF Protection
When a technician is working in areas not in compliance with the occupational, controlled area maximum permissible exposure and the situation cannot be controlled with engineering or work practice solutions, then personal protective equipment should be used. RF protective clothing should be worn to reduce the electromagnetic energy exposure.
The Naptex RF attenuation suit has work coveralls to protect the body and a hood to protect the head. Polyester yarn is wound coaxially around stainless steel fibers to produce the surface of the RF attenuation suit. Tests have demonstrated that the suit can effectively reduce EME absorption
within the body at virtually any frequency over the telecommunications spectrum by 10 dB to 12 dB. When working at lower frequency fields, the tower technician may be able to wear the suit without the hood.
Another tool for limiting RF exposure, the personal monitor, is an RF detector that alarms when the RF threshold (usually 50% of the occupational, controlled MPE) is exceeded. When nearing an antenna that needs maintenance, the tower technician can place the monitor near the antenna. If the monitor does not give an alarm, the technician can verify that the transmitter was deactivated.
Some manufacturers of personal monitors suggest that monitors can be worn to show compliance. The risk of this strategy is that when the monitor is operated in accordance with its instructions, compliance is only designated at the location of the monitor. If the tower technician would wear the monitor on a belt, it may give a false sense of security when the technician’s head and shoulders enter high RF fields without the belt-worn monitor giving an alarm.
Although the job of a tower technician has risks, those risks can be managed by diligently following safety guidelines.
OSHA GuidelinesIn response to requests from the tower construction industry, OSHA has issued guidelines that permit workers to ride a hoist line. These guidelines, revised as of Jan. 15, 1999, can be found on the OSHA Web site at http://www.osha-slc.gov/OshDoc/Directive_data/CPL_2-1_29.html#compliance.
The guidelines limit the number of workers riding the line to two, unless a personnel platform is used.
The guidelines make no provision for substituting the use of a vehicle in place of a hoist to raise the hoist line. The guidelines go into great detail regarding the maintenance and operation of the hoist, how the hoist must be configured, the training required for the hoist operator and safety procedures that must be followed.
Kipp is a broadcast engineer.
© 2002, PRIMEDIA Business Magazines & Media Inc. All rights reserved. This article is protected by United States copyright and other intellectual property laws and may not be reproduced, rewritten, distributed, redisseminated, transmitted, displayed, published or broadcast, directly or indirectly, in any medium without the prior written permission of PRIMEDIA Business Magazines & Media Inc.
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