[TowerTalk] RF RadHaz safety

[jimlux]

Patrick Barthelow wrote:
> 
> Relative to the pictures of KGO AM 810 TX antennas, referenced in an 
> earlier post, Some (all) of us who visited KGO, very much respected 
> the danger of touching the bare copper feed conductors going 
> to the base of each tower that were in easy hand reach.   
> Especially while squishing through the saturated saltwater 
> marshy mush of the ground at the 1/4 wave tower bases. A discussion 
> ensued among the hams, of whether any nasties would happen if you had to 
> do maintenance on the tower, while hot @ 50KW if you could safely jump 
> the ground to the insulated (hot) base of the tower.  Or even if not safe in
> the OSHA/FCC RAD HAZ sense, would  you would likely receive an 
> RF burn of any kind by hopping onto the tower never connecting to the
> ground and the tower at the same time?
>  
> Some say, you would feel nothing,
> others thought there could be significant charging current at 50 KW that
> you probably would get a painful, possibly dangerous ZAP, on contact, 
> even if not touching ground...
>  

There's a persistent myth in the tesla coiling hobby that "the rf 
current flows in the surface because of skin effect, so you don't feel 
it when doing the "sparks off the fingertips" thing".

Of course, the fact is that if you calculate it, the skin depth in human 
tissue at a few hundred kHz is something like meters.

Some of the folks building tesla coils happen to be neurologists and 
such, and their comment is that your nerves have a low pass filter 
characteristic around a few tens of kHz.  Therefore you can't feel the 
shock.  What you WILL feel is the thermal heating, but that takes 
longer. Or, if there's a spark that terminates on you, you get the burn 
at the point of entry.  Or, if the RF is pulsed, you might feel it.

There's also ample anecdotal evidence of workers in a strong RF field 
getting pains in their ankles and wrists from the current being 
conducted through their body. The ankles and wrists are relatively high 
resistivity compared to the rest of your body, so there's more power 
dissipated.

Jim