- Electrical safety
- Mains supply
- 50Hz via a live and neutral wire
- Live is at 240 rms volts
- Neutral is connected to earth at the substation
- If live wire makes a connection to earth, current can flow
- Damage
- Electrocution
- Current
- 1A = 6.24 x 10¹⁸ electrons/s. I = V/R
- Pathway
- LOC, VF, asphyxia, SCI depending on pathway
- 50μcA - microshock
1mA - tingling
15mA - muscle pain and tetany
75mA - VF
- Density
- Duration
- More damage with longer exposure
- AC vs DC
- As frequency approaches 1kHz, damage is less common. Most dangerous is 50 Hz
- Burns
- When electrons flow through resistance, heat is produced. Skin, when dry, has a high resistance so burns are generally most marked near the skin.
- Ignition of flammable substances
- How electricity flows through the body
- Resistive coupling
- Body earthed or connected to earthed piece of equipment
- Capacitive coupling
- Body acts as one plate of a capacitor
- Surgical diathermy
- Monopolar
- Energy at 200kHz to 6MHz
- Cutting has sine wave
- Coagulation has modified waveform
- Bipolar
- Lower power output
- No current passes through body
- Preventing electrocution
- General measures
- Maintenance & testing
- Ensure patient is not earthed
- Wear anti static shoes
- Equipment design
- BS5724/IEC601 standard
- Class I
- Connection of casing to earth via a wire. If becomes live, it melts the fuse.
- Class II
- Class III
- Type B
- Class I, II, or III
- Leakage current not > 100 μcA
- Type BF
- Type CF
- < 10 μcA so ok for direct connection to the heart
- Equipotentiality
- All terminals of each piece of equipment are connected to the same earth potential so currents cannot flow between them
- Floating circuits
- Circuit breakers
- Current operated earth leakage circuit breakers (COELCB)
- CEACCP
Link:ceaccp.oxfordjournals.org/content/3/1/10.full.pdf