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Safety Standards for EMF Exposures Lecture 9 January 29, 2016.

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Presentation on theme: "Safety Standards for EMF Exposures Lecture 9 January 29, 2016."— Presentation transcript:

1 Safety Standards for EMF Exposures Lecture 9 January 29, 2016

2 Current Approach to Setting the Standards 1. US approach – A. Find the lowest level where damage is observe reproducibly and set the level below this level by some safety factor. – B. Old USSR approach set the level below the lowest observed effects. – C. Implications of the different approaches

3 Electric Shock Table 1. Physiological Effects of Shock Electric Current (1sec. Contact)Physiological Effect Voltage required to produce the current with assumed body resistance: 100,000 ohms1,000 ohms 1 mAThreshold of feeling, tingling sensation.100 V1 V 5 mAAccepted as maximum harmless current.500 V5 V 10-20 mA Beginning of sustained muscular contraction ("Can't let go” current).1000 V10 V 100-300 mA Ventricular fibrillation, fatal if continued. Respiratory function continues.10,000 V100 V 6 A Sustained ventricular contraction followed by normal heart rhythm (defibrillation). Temporary respiratory paralysis and possibly burns.600,000 V6000 V Humans and animals are most susceptible to frequencies at 50 to 60 hertz because the internal frequency of the nerve signals controlling the heart is approximately 60 hertz. (Electric Shock Precautions) Source: (Nave & Nave) The National Electrical Code (NEC) in the U.S. considers 5 mA (to be a safe upper limit for children and adults; hence the 5 mA Ground Fault Interrupter (GFI) circuit breaker requirement for wet locations. (The Physical Effects of Electricity) The values in Table 1 should be used as a guide instead of absolute data points. For instance, 99% of the female populations have a “let go” limit above 6 mA with an average of 10.5 mA. 99% of the male populations have a “let go” above 9 mA, with an average of 15.5 mA. (The Physical Effects of Electricity

4 Body Resistance Table 2. Typical Human Body Resistance to Electrical Current Body AreaResistance (ohms) Dry Skin100,000 to 600,000 Wet Skin1,000 Internal body (hand to foot)400 to 600 Ear to Ear~100 Source: (Nave & Nave) Table 2 shows some of the typical human body resistances to electrical current. Barring broken skin, body-circuit resistance, even in contact with liquid, will probably be not less than 500 ohms. However, the current flow at this resistance and 120 volts is 240 mA—over twice what is required to cause death. (Biological Effects of Electric Shock)

5 Some History with Respect to RF and ELF Safety Standards 1. Debate on Thermal vs. Non-thermal Health effects from radar goes back to at least 1960s. 2. Wertheimer, N., and E. Leeper.1979. 3. Cordless phones, cell phone, WiFi 4. In all cases there are problems in going from the physics through the chemistry to the biology to possible health effects.

6 Basis for Setting RF Exposure Limits. 1. Based on extensive literature review and epidemiological studies. 2. Heating above normal tissue values by approximately 1C over about 6minutes 3. Do not consider other mechanisms such as changes in radical concentrations or the potential for long term effects or on sub populations such as children, sick people, or the elderly. 4. Does not include feedback and repair processes in the body.

7 On Average, My Temperature Is Just Right! 1

8 Current FCC Guidelines at RF Table 1. FCC Limits for Maximum Permissible Exposure (MPE) (A) Limits for Occupational/Controlled ExposureC Frequency Electric FieldMagnetic FieldPower DensityAveraging Time Range Strength (H) (S) │H │ 2 ∙ │H │ 2 or S (MHz) (V/m) (A/m) (mW/cm2) (minutes) 0.3-.3.0 614 1.63 (100)* 6 3.0-30 1842/f 4.89/f (900/f 2)* 6 30-300 61.4 0.163 1 6 300-1500 f/300 6 1500-100,000 5 6 (B) Limits for General Population/Uncontrolled Exposure Frequency Electric FieldMagnetic FieldPower DensityAveraging Time Range Strength (H) (S) │H │ 2 ∙ │H │ 2 or S (MHz) (V/m) (A/m) (mW/cm2) (minutes) 0.3-1.34 614 1.63 (100)* 30 1.34-30 824/f 2.19/f (180/f 2 )* 30 30-300 27.5 0.073 0.2 30 300-1500 f/1500 30 1500-100.000 1 30 f = Frequency in MHz *Plane-wave equivalent power density Source: OET Bulletin 56, 4 th ed., 08/1999, FCC

9 Electric Field Exposure Limits.

10 Limited Summary of Current Standards 1. At low frequencies the limits are set on the basis of electric fields large enough to fire a nerve cell. E ≈ 5kV/m for f< 368Hz 2 At RF exposure limits are set on the basis of heating or an specific absorption rate, SAR = 1.6W/kg over 1gram at 900MHz 3. Far Field exposures of P= 1mW/cm 2 for 6 minutes in the frequency range 30MHz to 300MHz

11 Statement of the Problem for the Standards Bodies. 1. The need to have something you can manufacture to, or conditions that allow you to install transmitters. 2. Second you know that over time the science is going to get better and you are going to see biological effects at lower levels and for exposures over longer periods of time. 3. The problem is where do you set the numbers and how do you adjust them at a later date.

12 Standards Setting 4. If you change the standards – A. What are the economic implications and health implications? – B. What you do about the imbedded equipment? 5. What are risks to you take and at what cost by setting the standards at any given level?

13 Loss of life expectancy and total number of lost days CauseDaysCauseDays Being unmarried-male / female3,500 / 1,600Average job accident74 Cigarette smoking-male / female2,250 / 800Drowning41 Heart disease2,100Falls39 Being overweight 30% / 20%1,300 / 900Fire-burns27 Being a coal miner1,100Generation of electricity24 Cancer980Suffocation13 Low Socio-economic status700Fire arms accidents11 Living in unfavorable state500Natural radiation / From nuclear industry8 / 0.02 Army in Viet Nam400Medical x-rays6 Smoking Cigar / Pipe330 / 220Poisonous gases7 Job Dangerous / with RF exposure / safe300 / 40 / 30Coffee6 Accidents Motor vehicle / to pedestrians207 / 37Oral contraceptives5 Pneumonia, influenza / Diabetes141 / 95Reactor accidents-UCS / RCS2 / 0.002 Alcohol (US average)130PAP exams-4 Accidents in home 95Smoke detector in home-10 Suicide 95Air bags in car-50 Legal drug misuse90Mobile coronary care unit-125 Average job accident74Safety improvement ‘66-’76-110 Source: Cohen, Bernard L. And Lee. I-sing, “A Catalog of Risks.” Health Physics (36) 707-722. 1979.


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