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MINIMUM THRESHOLDS FOR PHYSIOLOGICAL RESPONSES TO FLOW OF ALTERNATING ELECTRIC CURRENT THROUGH THE HUMAN BODY AT POWER-TRANSMISSION FREQUENCIES

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J. C. Keesey, F. S. Letcher · 1969

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Just 0.1 milliamps of 50-60 Hz electrical current can be perceived by 1% of the population, revealing human sensitivity to extremely low electrical exposures.

Plain English Summary

Summary written for general audiences

This 1969 Naval Medical Research Institute study examined how much electrical current from power lines (50-60 Hz) causes measurable responses in humans. Researchers found that 1% of people can perceive currents as low as 0.1-0.5 milliamps, while 99% of adult males can release their grip at 9 milliamps before losing muscular control.

Why This Matters

This foundational research established safety thresholds that remain relevant today as we grapple with increasingly complex EMF exposures. While this study focused on direct electrical contact rather than wireless radiation, it demonstrates how even extremely low currents can trigger physiological responses in sensitive individuals. The finding that just 0.1 milliamps can be perceived by some people underscores the reality that human biology responds to electrical phenomena at levels far below what many consider 'safe.' What's particularly striking is that the study's recommended 5 milliamp safety threshold was based on preventing any current above an individual's release threshold - a precautionary approach that contrasts sharply with today's EMF safety standards, which often dismiss biological effects that don't cause immediate tissue heating.

Exposure Information

Specific exposure levels were not quantified in this study.

Cite This Study
J. C. Keesey, F. S. Letcher (1969). MINIMUM THRESHOLDS FOR PHYSIOLOGICAL RESPONSES TO FLOW OF ALTERNATING ELECTRIC CURRENT THROUGH THE HUMAN BODY AT POWER-TRANSMISSION FREQUENCIES.
Show BibTeX
@article{minimum_thresholds_for_physiological_responses_to_flow_of_alternating_electric_c_g4016,
  author = {J. C. Keesey and F. S. Letcher},
  title = {MINIMUM THRESHOLDS FOR PHYSIOLOGICAL RESPONSES TO FLOW OF ALTERNATING ELECTRIC CURRENT THROUGH THE HUMAN BODY AT POWER-TRANSMISSION FREQUENCIES},
  year = {1969},
  
  
}

Quick Questions About This Study

One percent of the general population can perceive between 0.1 to 0.5 milliamps of 50-60 Hz current from power lines, depending on the type of hand contact made with an electrically-energized circuit.
The 5 milliamp safety threshold was recommended because any 50-60 Hz current exceeding an individual's release threshold should be considered hazardous and potentially lethal, providing a protective margin for the general population including children.
Yes, 99% of adult male workers should be able to release their grip when exposed to 9 milliamps of 50-60 Hz current before experiencing uncontrollable muscular contraction that prevents letting go.
Researchers identified three measurable physiological responses to 50-60 Hz electrical stimulation: perception of electric current flow, uncontrollable muscular contraction preventing release, and death from electrical shock.
Voltages calculated from reliable experimental data on effective currents and expected body resistances were found to be lower than voltages generally recommended as safe at the time.