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Shively Antenna Burn

J

jambox

Hi

We recently had a Shively 6814 6 bay burn. When I disassembled the top plate with the pressure spring valve, there was an over whelming smell of chlorine. When I got closer to the transmission line and took another wiff, my eyes and nostril were burned. It was beyond a doubt, chlorine gas. I have been doing this for 33+ years and had my share of antenna burns and never experienced this before. Have any of you fellow engineering type sun accros this before? And if so, who was the antenna manufacturer when it happend. I've called ERI, Dielectric and Shively and they have never heard of this happening. Also, there was a fine yellowish-green dust on all the surfaces above the top bay and the inner line termination looked corroded. Thanks!
 
That's one of the strangest stories I've ever heard! I'm curious - is the line pressurized and if so how are you doing it? Dehydrator? Nitrogen? The first thing that popped in to my head when I read your post was that your Nitrogen tank wasn't really nitrogen at all.

C-
 
plastic insulation burning-- e.g. PVC is, after all, polychloride vinyl--has chlorine in its composition.
Either in the antenna or feedline. Probably result of overheating in a closed -off, oxygen-deprived environment.
 
From the Houston Wire and Cable website:

"Two halogens-chlorine and fluorine-are extensively used in compounds for insulating and jacketing electrical wire and cable. Many common materials like PVC, Hypalon®, Neoprene®, and FEP and PTFE Teflon® contain significant amounts of these halogens. PVC, for example, contains 29% chlorine by weight; CPE 19% chlorine by weight; and Teflon has 76% fluorine by weight.

Halogenated compounds are normally very stable. When they burn, however, the halogens separate and become highly reactive, forming very toxic, extremely dangerous and corrosive gasses that can significantly damage organic, inorganic and metallic materials. The hydrogen chlorine gas produced from burning PVC, for example, is similar to mustard gas."

You're pretty lucky you didn't get overwhelmed by that stuff.
 
also, another point I would to make... Chlorine gas is significantly heavier than nitrogen. It tends to stay low to the ground. Why would it be stuck up in the top of an antenna's 1/4 wave shorting stub (a space of 28 inches by 4 inches in diameter) , on the end of 1,800 feet of 6 1/8" transmission line? It's a curious thing...
 
Grich

If Chlorine gas is a common by product of teflon burning, why isn't this issue more commonly reported...? The insulators in 4" transmission line that is designed to handle 80 Kw rf at FM frequencies has to have a higher dielectric standard than the wire insulation of electrical wire. It only has to handle a breakdown voltage of at best a few thousand volts, 480 for most commercial buildings. Regular teflon is not a good dielectric at FM frequencies.
 
Good question. Of course, fire departments are keenly aware of the effects of burning wire insulation, and I'm sure toxic gas generation is part of the reason standard PVC-jacketed cable is not supposed to be used in plenum spaces unless it's in conduit.
 
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