Weather radar
 

I was wondering can any body tell me something about radiation from weather radar, and it's hazard to human health, I am talking about us who are seating in cockpit

I wouldn't suggest that this thread tells it all .. but read Lu's tales and ponder upon what it might mean in terms of your question ... ?

The current crop of radars only has an output in the order of 125 watts max. That would be for the Collins 700 series or Honeywell RDR4.
Some of the older ones put out considerably more and did in fact represent a danger if you put yourself in the beam.
The DC9's had an antenna that rotated 360 degrees but the radar wasn't transmitting when the antenna was less than 90 degrees ofset to the fuselage and there is radar absorbing matting on the bulkhead.
Danger to the pilot? Virtually nonexistant. To the technician? There have been incidents.

FlapsOne has it right in john_tullamarine's link.

Average power for a modern Wx Radar as fitted in the B747-400 is around 24 Watts and the minimum safe distance on transmit is 14 to 15 feet. That is not true of the 'toasters' fitted in older machines, some of them, like the old Bendix unit that avioniker mentions above, can produce dangerous radiation for hundreds of feet ahead. There's not many of those older units left nowadays though and low power radars have been more or less standard BFE in large transport aircraft built since the late seventies and early eighties.

Military interception radars are another story, and many can cause the effects described in the link by Lu Zuckerman, but then they are airborne search radars, with concentrated high power beams tuned to detect other aircraft.

The answer is, its safe to turn on your Wx Radar during taxi if it is a modern digital low power unit. If you don't know what you've got, ask to consult one of your company's avionics technicians.