Yes there is no real risk in most cases, all that is needed is folk to think a bit about the more extreme cases.

The other issue is that if nothing is calculated ever, you leave the gates open to folk claiming injury from fields whose strength you cannot even provide an estimate for - even if the answer was they are at a level of no concern at all. It is good to have the numbers to close that sort of argument down before it starts.


Note that it is not made clear but for HF and VHF there is an averaging time to consider - the body can dispose of quite a lot of heat - several hundred watts actually if it is spread over the whole body, by raising heart rate, dilating blood vessels  and sweating, but it is not good to do this for a long time.

In some designs of  MRI scan the whole body RF  dose is about a kW, but only for  a matter of minutes, and there is aircon, so the body starts cool and does not have time to get too hot by the end. The same kW concentrated into say the head only however would be very serious indeed, and  even ten watts, if just into one eye or ear, would also be bad news.


For most Ham radio frequencies and distances of more than a body length, this slow heating  is the dominant problem, so  a short flash of 10 times the limit power for a few seconds followed by 90% of the time off, is also not an issue - the example of the mobile transmitter comes into that category for any other car or pedestrian, unless you are stuck in a traffic jam.

With microwaves the penetration is less, so the energy is all dissipated near the skin - which is bad in that it is concentrated in a small volume, but not so bad in that the skin is much better cooled than say internal organs.


To get a feeling of RF cooking powers, I once had dealings with parts designed for a 27MHz system  where with 40kW -50kW of RF a box of a meter cube or so  was specified as capable of thawing and heating approximately 1 tonne of frozen chickens per hour on a conveyor belt...


Mike.

Yes there is no real risk in most cases, all that is needed is folk to think a bit about the more extreme cases.

The other issue is that if nothing is calculated ever, you leave the gates open to folk claiming injury from fields whose strength you cannot even provide an estimate for - even if the answer was they are at a level of no concern at all. It is good to have the numbers to close that sort of argument down before it starts.


Note that it is not made clear but for HF and VHF there is an averaging time to consider - the body can dispose of quite a lot of heat - several hundred watts actually if it is spread over the whole body, by raising heart rate, dilating blood vessels  and sweating, but it is not good to do this for a long time.

In some designs of  MRI scan the whole body RF  dose is about a kW, but only for  a matter of minutes, and there is aircon, so the body starts cool and does not have time to get too hot by the end. The same kW concentrated into say the head only however would be very serious indeed, and  even ten watts, if just into one eye or ear, would also be bad news.


For most Ham radio frequencies and distances of more than a body length, this slow heating  is the dominant problem, so  a short flash of 10 times the limit power for a few seconds followed by 90% of the time off, is also not an issue - the example of the mobile transmitter comes into that category for any other car or pedestrian, unless you are stuck in a traffic jam.

With microwaves the penetration is less, so the energy is all dissipated near the skin - which is bad in that it is concentrated in a small volume, but not so bad in that the skin is much better cooled than say internal organs.


To get a feeling of RF cooking powers, I once had dealings with parts designed for a 27MHz system  where with 40kW -50kW of RF a box of a meter cube or so  was specified as capable of thawing and heating approximately 1 tonne of frozen chickens per hour on a conveyor belt...


Mike.