TABLE 33: RFR SHOCK AND BURN
| Authors | Effects Sought or Examined | Exposure Modality | Effects Reported | Notes & Comments | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rogers (1981) | Threshold currents for barely perceiving a sensation and for feeling discomfort from touching or grasping a body energized by RF. | Touching or grasping contact with a brass tube excited from a grounded RF source at frequencies in the MF (0.3-3 MHz) or the HF (3-30 MHz) bands. | Using the apparatus, the author measured the threshold "perception" current (for barely perceptible sensation) and the threshold "let-go" or "hazard" current (that caused discomfort) for frequencies in the MF band (0.3-3 MHz) and the HF (3-30 MHz) band. The perception current and let-go current for contact with the tip of the forefinger were both about twice those for contact with the back of the forefinger, and were even higher for large-area contact with the palm. For 50 persons who touched the tube with the back of the forefinger, the mean hazard threshold current was about 200 mA for the band 2-20 MHz. The author remarked that RF burns could occur from touching structures exposed at field strengths much lower than those in the ANSI (1974) guidelines. | The brass tube was part of a simple "RF Burn Hazard Meter" for measuring the RF currents passing through a human in shoes standing on a ground plane. A subject touching the tube thereby became part of a closed loop through which the RF current flowed and was measured.
| Gandhi and Chatterjee (1982)
| The authors calculated short-circuit currents induced in 4 metallic objects and a human, all assumed insulated from ground, when each is exposed to an RF electric field at 10 kHz to 10 MHz. They also calculated the RF fields for threshold-perception and let-go currents in a human in finger contact with each object. Used were the threshold data of Dalziel and Mansfield (1950), Dalziel and Lee (1969), and Rogers (1981).
| The electric fields were assumed to be vertically polarized. The metallic objects were: a 2.44-m by 1.22-m metal roof, a 50-ft metal fence, a compact car, and a fork-lift truck. The human was assumed to be of height 1.75 m, mass 68 kg.
| Log-log plots of the calculated values of electric field E necessary to create threshold-perception and let-go currents in a human in finger contact with each object showed that E for threshold perception was constant for each object in the approximate range 10-100 kHz, with values about 250, 160, 80, and 20 V/m for the roof, fence, car, and truck. In the range 10 kHz to 10 MHz, the E values for the car and truck did not change much but those for the roof and fence decreased to about 35 and 20 V/m at 10 MHz. Plots of E for let-go current were similar: the plateaus for the roof, fence, car, and truck in the range 10-100 kHz were about 1040, 850, 440, and 110 V/m, with diminution for the roof and fence to less than 100 V/m at 10 MHz and smaller decreases for the car and truck. The authors noted that threshold E values higher than those in the ANSI (1982) guidelines may be encountered.
| The authors defined threshold-perception current as the smallest current that yields a tingling or pricking sensation due to nerve stimulation. They indicated that the sensation changes from tingling to internal heat at frequencies above about 100-200 kHz. Let-go current was defined as the maximum current for which a human can still release an energized conductor with muscles directly stimulated by that current. The experimental threshold data of the cited authors were reproduced as log-log plots of perception-threshold and let-go currents versus frequency.
| Gandhi et al. (1985a)
| Chatterjee et al. (1986) Measurements of human body impedances and threshold currents for perception and for pain versus frequency in the range from 10 kHz to 3 MHz.
| Currents induced: in humans near local AM stations and Coast Guard and Navy sites while barefoot or with 3 types of shoes; in a small car, a van, and a school bus; and in humans in contact with such vehicles. Barefoot humans on a ground plane while grasping an insulated brass rod or touching an insulated metal plate with a saline-wetted index finger.
| AM-station broadcast frequencies: 630, 700, 1500 kHz; Coast Guard and Navy frequencies: 13.6, 23.4, 146, 3105 kHz. For men, the mean threshold-perception currents for finger contact rose with frequency from about 4 mA at 10 kHz to 40 mA at 100 kHz and remained there from 100 kHz to 3 MHz. The plot for women was parallel, but about 25% lower, a highly significant difference. The results for grasping contact were similar. The plots of threshold currents for finger-contact pain rose to maxima at about 100 kHz but decreased slightly in the range 100 kHz to 3 MHz. At 10 kHz, the mean threshold currents for pain in men and women were about 10 and 6.5 mA, but their maxima at 100 kHz were both about 14.5 mA.
| Electrical safety shoes and gloves were found to provide adequate protection only at frequencies less than about 1 and 3 MHz, respectively. The threshold-perception plots for finger contact by men, women, and children were entirely below 632 V/m, the value recommended in ANSI (1982) for the range 0.3-3.0 MHz. The sensation for frequencies below 100 kHz was tingling or pricking localized in the area next to the contact region; above 100 kHz, the sensation for finger contact with the plate was warmth or heat in the area below and around the plate; with grasping contact, warmth or heat was felt in the hand and wrist. The sensation at 50 kHz was tingling, but at 70 kHz, some subjects reported tingling and others warmth, with a change for the former to warmth at higher current.
| Guy and Chou (1985)
| Shock and burn hazards in the VLF-MF range; perception and shock thresholds under various conditions.
| Human impedances and distributions thereof within human bodies; impedances of various vehicles and of humans in contact with such vehicles. Induced body currents and current densities in humans; SAR distributions and mean SARs in all parts of the human body. Various human and vehicular exposure modalities at 10 kHz to 3 MHz. Human exposures to specific VLF-MF frequencies at sites in Hawaii and Washington State.
| Highest local SARs occur in the ankles of humans, a result also found by Gandhi et al. (1985a). Permitted in ANSI (1982) were exposures at maximum local spatial SARs as high as 8 W/kg if whole-body-averaged SARs do not exceed 0.4 W/kg, which led the authors to remark that exposure to fields in the VLF-MF range would have to be restricted to 97 V/m to avoid exceeding the 8-W/kg limit. They also indicated that for VLF-MF exposure, absorption from the magnetic component is usually at least 10 times lower than from the electric component, implying that exposure guidelines should reflect such differences.
| The authors noted that in the VLF-MF band, quantities other than SAR may be more important because energy absorption by humans in that frequency range are relatively low but can cause direct neuromuscular effects from electric shock, and that local tissue damage may result from electric contact between subjects and RF-exposed metallic objects.
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