RF Safety Training.com

RF Safety Applications

 

Tower climber

 

Tower CAUTION sign

Tower Climbing

The risks for exposure to significant levels of RF radiation are higher for tower climbers than they are for perhaps any other occupation. While the RF field levels on many towers—such as those that contain only cellular antennas—are not very high, the RF field levels near FM radio and television antennas are extremely high. A tower climber who gets near the aperture of one of these antennas while it is transmitting at typical power levels can be exposed to RF fields that are very dangerous—literally several thousand percent of the FCC’s Maximum Permissible Exposure (MPE) limits for Occupational/Controlled exposure.

One case for an FCC Notice of Apparent Liability for Forfeiture (NAL) provides a good example of how things can go very wrong for a tower climber. In this case, the climber was wearing an RF protective garment (RF suit) and an RF personal monitor. He initially climbed the tower after the power levels of all three FM antennas on the tower had been reduced to about 10 percent of their normal operating levels and found that even at reduced power, the RF field levels were still too high. Once he had determined that the three FM transmitters had been turned off, he removed the hood of his RF suit and shut off his personal monitor, and climbed back up the tower. While it easy to understand why the worker would want to remove the hood for visibility, it is difficult to fathom why he would turn off his personal monitor. (Perhaps it was to save the battery?!) When the climber noticed that his legs were getting warm, and the RF suit had started smoking (not a good sign!), he knew that the power had been turned back on and scurried back down the tower. He then found out that two of the three FM stations were back on the air at full power! Read the Smoking Suit NAL.

There are countless stories of incidents similar to the one described above. Most involve having the transmitters turned back on while the climber is still on the tower. Many times it has had something to do with local versus remote control—where an individual at a remote location turned the power back on (or increased it back to full power), unaware of what was going on at the tower site. These incidents demonstrate why a proper lockout, tagout (LOTO) procedure should be in place whenever personnel are on the tower. It is especially important to make sure that remote operation is disabled for broadcast systems!

Start with a good LOTO procedure if you are going to turn the power completely off. But tower climbing is often performed with reduced RF power. Under these conditions, LOTO procedures are of little value unless they can be modified to control the power level rather than the ON/OFF function. This is where RF personal monitors come in—they should be worn by anyone who goes up a tower with FM radio or television antennas. They should be worn whether or not the climber is going to wear an RF suit.

One important point that must be considered is that standard RF personal monitors are of little value when used in conjunction with RF suits. Standard monitors are set to alarm at 50 percent of the MPE limits for Occupational/Controlled exposure, allowing for 3 dB of measurement uncertainty. RF suits with hoods conservatively allow the wearer to work in RF fields up to10 times the normal limit, i.e. 1,000 percent of the MPE limit. But many climbers operate under the mistaken assumption that if they put a standard RF personal monitor under their RF suit, it will warn them when the fields inside the suit exceed 50 percent of the MPE. Unfortunately, the RF personal monitors simply do not function correctly when worn under these conductive suits. There are strong fields created close to the suit and current running through the fabric. Although there is an occasional false alarm, most times the monitors are simply inhibited and will never sound an alarm. Thus the climber ascends the tower with a false sense of security thinking that the monitor will sound when he or she is being overexposed. The only product that addresses this application is the special high-power version of the Nardalert XT, which is designed to be worn outside an RF suit. This monitor functions in RF fields up to 1,000 percent of the MPE for Occupational/Controlled exposure. This is the level recommended as the maximum field level for tower climbers wearing RF suits. This monitor is available from RF Safety Solutions. Nardalert XT RF Personal Monitors.

While the benefit of wearing an RF personal monitor is obvious for a climber going up a tower with active antennas, many people believe that a monitor is not required if the power is going to be shut off. In the RF safety programs developed by RF Safety Solutions, monitors are always required for personnel who climb towers with FM radio and/or television antennas—even when the power is supposed to be off. The cited NAL reinforces our belief that, as a minimum, they are a redundant safety procedure. But given the number of times that incidents similar to the one described in the NAL have happened, wearing RF monitors under all conditions just makes sense.

What else do you need besides LOTO equipment, an RF personal monitor, and perhaps an RF suit? You need a plan! If you are going to be working near broadcast antennas, it is important to have a plan specific to that tower. And nowhere is it more important to have a good plan than when other antennas on nearby towers are involved. Consider a site like Mt. Wilson. This large antenna farm northeast of Los Angeles has more than 30 towers. Many of the towers in the central area of the mountaintop are 50 to 100 feet from each other. It takes a great deal of cooperation and coordination in order to safely climb towers in an environment like this.

 

If you have concerns or questions about RF safety on towers, contact us.