RF safety

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I just was sent a copy of IEEE Std C95.1, 1999 edition:
IEEE Standard for Safety Levels with Respect to Human Exposure to RF 
Electromagnetic Fields, 3kHz to 300 GHz..

This is an update of the earlier 1991 standard.  I suspect that most of the 
changes have to do with exposures in higher frequencies than we fool with 
in tesla coils, but, there was some interesting stuff.

I leave it to others to evaluate what sorts of fields result from the 
typical TC...


They have limits (MPE = Maximum Permissible Exposure, which includes some 
safety factor) for grasping contact. (where sparks,startle, etc. aren't an 
issue)

The spec calls for a maximum RF current (averaged over 1 second) of 1000 f 
mA, where f is in MHz, and this applies from 3 kHz to 100 kHz. From 100 kHz 
to 100 MHz, the maximum current is 100 mA.  For induced currents, it's that 
value per foot (i.e. if the current passes through both feet, you can be 
exposed to 200 mA).  The current can be calculated (or measured) using a 
model of the human body impedance. They have charts, and there's a lot of 
variability (50%), but here's some numbers (error bars on Zmag are about 60 
ohms and 2 degrees for phase).  The first number is for males (where it's 
the top of the error bar, the second for females (where it's the bottom of 
the error bar).

Frequency(kHz)	Zmag	Phase
10		500/630	12/11	
30		480/580	10/9
100		420/540	9/8
300		400/500	7/7
1000		380/480	5.5/6
3000		350/450	6.5/7


For the field limits.. in controlled enviroments
3-100 kHz, 614 V/m E field, 163 A/m H field, 6 minute averaging time
100-3000 kHz, 614 V/m E field, 16.3/f A/m H field, 6 minute averaging (f in 
MHz)

For pulsed fields, in the range 100 kHz-300 GHz, peak E field must be < 
100kV/m and for pulses <100 ms (i.e. TC output), the MPE is the value from 
above (614 V/m) adjusted as follows:

Peak MPE = MPE * Averaging time in seconds(i.e. 360)/ (5 * pulse 
width(seconds))

A max of 5 pulses calculated as above with a time between pulses > 100 ms 
are permitted in the averaging interval. For higher PRF you just average 
over the interval (6 mins), except that in any 100 ms period the sum of the 
peakMPE*pulsewidth = MPE *averagingtime/5