Don't become a statistic

January 1, 2008

Broadcast engineering history includes a number of accidental deaths. By its very nature, working with high voltages, heavy equipment and tall towers, is an invitation to trouble. Since the development of radio transmission, a number of well-known (as well as many relatively unknown) engineers have unfortunately lost their lives through even such lamentable accidents as raising a field strength-measuring antenna into a power line over a measuring truck in the dark.

Always have a second person present when working around any high-voltage equipment.

Always have a second person present when working around any high-voltage equipment.

It used to be said that you could distinguish radio engineers by the burns on their hands and forearms, generally produced by RF when working with transmitters and antenna systems. It seems to me that RF alone was not usually solely responsible for many fatalities in our field.

There are many lists extant of precautions to take before working with high voltage pieces of equipment. Lethal incidents may be more often caused by completely unexpected circumstances than from pure, careless accidents.

Unusual incidents

More than 50 years ago I was director of engineering and general manager of CHCT-TV, Calgary, Canada. Canadian GE was supplying and installing the super turn-style antenna on our 600-foot tower about 20 miles west of Calgary. A fair number of people had gathered to watch and the RCMP was keeping the crowd at least 1,000 feet away from the base of the tower. Just before the antenna raising commenced, one of the riggers asked to ride on the antenna as it was hauled up, in case it fouled the tower or the guys. I said, “No, climb the tower in pace with the antenna.”

The winch started and the antenna began to ascend. It rose slowly and smoothly until, when at about 400 feet, a very strange sound was heard. It was a keening, flute-like note, probably around 3 to 4kHz. The winch stopped.

Suddenly the antenna began to fall! I was concerned lest it foul the guy wires or the central mounting pipe struck the tower and brought it down, too. Very quickly the bottom of the pipe struck the footing and the ground. There was a strange puff of red smoke (the red beacon glass had disintegrated upon impact and I could not find a single piece of red lens at the base of the tower) as the pipe entered the ground for about 7' and gouged the side of the footing. The pipe was bent, two antenna sections were wrecked and one damaged. The rigger who wanted to ride the antenna came down the tower looking rather white and said to me, “Thank you.”

The hoisting cable had failed due to a kink occurring the previous week when another station's antenna was being raised in Saskatchewan. Apparently no one had been concerned about this. The strange flute-like sound was that of the individual strands of the metal cable breaking at the kink. This was truly an accident waiting to happen.

Always verify that no voltage is present before going in.

Always verify that no voltage is present before going in.

Another potentially fatal accident occurred when we were tuning the transmitter of KAVE -TV, Channel 6, Carlsbad, NM. We had finished installing the transmitter and all the tubes, including a set of mercury vapor rectifiers across the open lower front of the PA cabinet, and applied power. Everything seemed to be working and I was tuning the final.

Suddenly someone hit me on the back of my neck with a baseball bat and at the same time someone else hit me in the groin with another baseball bat. I sank to the floor. There was a smell of burnt clothing and my right knee was very sore. After a moment, I got up, killed the high-voltage circuit and replaced the bottom section of the front of the PA cabinet. This prevented other careless people's knees from contacting the top caps of the 9kV mercury rectifier tubes of the high-voltage supply. I was lucky to be alive. My right hand had been on the metal cabinet and my right knee came in contact with the top cap of a 9kV power supply — good conditions for electrocution.

This next incident was the kind of thing that could happen to anyone, but should not, if all safety rules are followed.

WKYC, 1100kHz 50kW Cleveland, OH, had been sold to WWWE, which was running the original 100kW Westinghouse transmitter minus one modulator and one power amplifier tube at 50kW while waiting for a new transmitter.

One morning the phone rang in my office and Charlie said, “John, we've got no audio”. At that time we were operating WWWE with local manual transmitter control. I verified that audio was leaving the studio and Charlie, the transmitter engineer, confirmed it was reaching the transmitter. He opined that it was the modulation transformer. I told him I would be right out and to check connections and overall operation, but not to open the transmitter until I got there. I always insisted on two men when working on a transmitter.

About 10 minutes later, I arrived, assessed the situation and agreed that it probably was the modulation transformer. We switched off the transmitter and heard the usual clatter as safety-shorting connections, killed the transmitter high-voltage bus and went to the 25-square-foot high-voltage room. I was carrying the grounding stick and as we opened the door I heard another grounding safety drop into place.

We approached the modulation transformer, which was several feet high with a large four-microfarad capacitor mounted on it. Charlie pointed out the connections to the primary and said, “It looks as though there is corrosion, I bet that's the problem.” He proceeded to reach out his hand toward it. I frantically hit the connector with the grounding stick and yelled, “Don't touch it!

There was a blinding flash and a deafening bang as the four-microfarad capacitor, hooked to the top of the modulation transformer, discharged 11kV through the grounding stick instead of Charlie. He turned white.

This near fatality showed the tremendous importance of following standard safety procedures, which include hanging a grounding stick on equipment where work is performed. Charlie went by the sounds of grounding contacts going into place when the transmitter was turned off, and he placed his confidence in the completeness of the high-voltage grounding procedures. He didn't remember that when some components and circuits fail, other capacitors and circuits could be left energized because of incomplete grounding.

The best way to become an old experienced engineer is to assume that every circuit is hot until it is grounded at both ends.

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