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# Do not understand RF biological effects 4W/kg

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#### BiNa2605

##### Full Member level 3
Hi everybody,

I read the paper and it has the sentence like that but I don't know exactly the meaning:
that the most heat the human body can deal handle without risking permanent damage is approximately 4 W/kg.

I am not sure 4W/kg that is the limitation of the power output of RF reader or if a person weights 60 kg that is the threshold of the output radiation is 4W*60 :bang::bang::bang:

#### chuckey

I do not recognise 4W/kg as any RF related threshold. Is it not the amount of heat a body can dissipate without raising the bodies internal temperature to a dangerous level?
The RF safety levels are 10mW/cm^2 or 100V/m.
Frank

BiNa2605

### BiNa2605

Points: 2

#### BiNa2605

##### Full Member level 3
Actually I am not have the equitment to measure the power per centimet, I just consider the power output of RF reated to health.
Do you know the level of output power of RF wave still safe for health? (Power and time for radiation expose).
This is one of paper's quote: "It was determined that the most heat the human body can deal handle without risking permanent damage is approximately 4 W/kg. To put things in perspective, the normal metabolic rate when someone is sleeping is about 1.0 W/kg. It increases to about 2.0 to 2.5 W/kg during moderate exercise. Much of this research was based on exercise levels rather than on actual exposure experiments. This is because exposure to significant levels of RF energy is very similar to the effects of overexertion."

#### FvM

##### Super Moderator
Staff member
W/kg values are used in regulations dealing with specific absorption rate (SAR), e.g. for mobile phones. See https://en.wikipedia.org/wiki/Specific_absorption_rate

Just quoting SAR numbers isn't of much use, you need to refer to the specific conditions. High values like 4 W/kg are accepted either for local and/or short time exposure (e.g. caused by mobile phones) or in special situations, e.g. medical tests.

BiNa2605

### BiNa2605

Points: 2

#### chuckey

If you weigh 80 kg, then the "safe " power would be 320W. Would you look down a wave guide carrying that amount of power, because it would blind you. The 100V/m is used at low/medium/high frequencies where some one has calculated either the heating effect over the whole body because the wavelength is long or the peak RF current that could flow through the heart.
I can only think that the 4W/kg is somehow based on the heating effect of RF current in the head and the heat is being pumped away in the blood and "sweated" out. It seems unrealistic as a mobile device would be unlikely to run this sort of power. Even the brick phones only ran about 5W.
Frank

BiNa2605

### BiNa2605

Points: 2

#### dick_freebird

I wouldn't place a lot of credence in a general number.
Some meat cooks easier than others. Eyeballs for example.

#### BiNa2605

##### Full Member level 3
@chuckey How do you think about when the RF just focus on 1 place of the body for along time? So I think in that case we cannot calculate by multiple 4W*x(kg). @FvM said right, we should consider the specific absortion rate (SAR), it is more acadamic and accurate.
@dick_freebird I understood what you mean Brain, eyeballs and body organs are really sensitive and be eaiser effected by RF.

#### chuckey

The levels I gave are for continuous exposure, i.e. an aerial engineer. Short term exposure is a gamble as to where the RF power hits the body.
FWIW The Russians have detected changes in biological cells at a power level of 1mW/cm^2. Its like cancer, how long would it take for a biological cellular injury show as an obvious disease or injury.
Frank

#### D.A.(Tony)Stewart

I am not sure 4W/kg that is the limitation of the power output of RF reader or if a person weights 60 kg that is the threshold of the output radiation is 4W*60 :bang::bang::bang:

These limits are based on averaged whole body RF conductance from heat rise , not near-field RF levels.

I recall leakage from a 100W VHF amp being tuned by an RF tech without the lid on would get bloodshot eyes after a day's work.

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