1. Electrical Safety BiomedE / EECS 458 Reading: Webster, Chapter 14

2. Electrical Currents in body Vstim ~ R skin R internal Three phenomena are possible through electrical currents Electrical stimulation of excitable tissue (nerve & muscle) Resistive heating of tissue Electrochemical burns and tissue damage

3. Physiological effects of electricity Conditions: 70-kg human, moistened hands, AGW #8 copper wire

4. Variability of Perception Thresholds and Let-go Currents Physiological effects of electrical shocks depend on body size ( among other factors)

5. Let-go Current vs. Frequency 60 Hz

6. Fibrillation Current vs. Shock Duration

7. Effects of Entry Points on Current Distribution Microshocks -- currents as low as 20 uA can induce cardiac fibrillation

8. Electric-power Distribution

9. Macroshock Hazards Most instruments have grounded or non- conductive cases

10. Leakage-current Pathways

11. Ground-fault Currents

12. “Equivalent Resistance Guy” Skin surface Sub-dermal surface Skin resistance (15 k Ω to 1 MΩ/cm 2 ) Internal body resistance (100- 200 Ω -- limb, trunk)

13. Erg in intensive care ECG monitor (lead I) EEG monitor (single lead) Catheter in right arm for IV drug infusion through automated system Each system is plugged into a separate wall outlet

14. Erg’s bedside schematic Outlet 1 Outlet 2 Outlet 3 sig H N G1 G3HNG2 H N ~G3 EEG ECG Pump

15. Erg’s bedside schematic Outlet 1 Outlet 2 Outlet 3 sig H N G1 G3HNG2 H N ~G3 Vgl ~ Ground loop currents!! EEG ECG Pump

16. Erg’s bedside schematic Outlet 1 sig H N G1 HN H N ~G1 Solution: Single power distribution node with a common ground EEG ECG Pump

17. Grounding System

18. Isolated Amplifier