Ferris et al. 1936 sets ~0.1 ampere at 60 Hz, hand-to-foot, for shocks of 3+ seconds, as the practical danger threshold for man

bell-labselectrical-safetyquantitativecardiologyprimary-sourcehop

Across the seven-species fibrillation-threshold experiments, the authors found average fibrillation-threshold currents of 0.26 A (scaled to a 70 kg body weight) and 0.29 A (scaled to a 330 g heart weight). From those thresholds they draw the paper's headline, practically-oriented, lower-bound conclusion directly: "The results on the whole indicate for man that currents in excess of 0.1 ampere at 60 cycles from hand to foot would be dangerous for shock durations of three seconds or more." The 0.1 A figure is deliberately conservative relative to the measured animal averages — a safety margin built into the recommendation, not the experimental result itself.

This is the specific number the Bell-Labs-adjacent line of electrical-safety research is best known for downstream, and it now traces to the primary text rather than a secondary retelling: a direct PDF extraction of the BSTJ digest, quote verified against the document itself.