Electrical safety

Question 1

UK mains supply details

Answer 1

AC
50hz
oscillates between +340 and -340v
rms voltage 240V

Question 2

What is class 1 electrical equipment

Answer 2

earth wire

Question 3

what is class 2 electrical equipment

Answer 3

extra insulating casing

Question 4

what is class 3 equipment

Answer 4

powered internally by battery or by SELV

Question 5

What are the specifications for SELV?

Answer 5

Voltage not ?25V AC
Not >60V DC
No earth connection
Low risk of accidental contact with higher voltage

Question 6

WHat is the difference between macroshock and microshock

Answer 6

macroshock is where current flows from intact skin to skin
Micros shock is when skin is breached or aberrant currents are delivered directly to myocardioum

Question 7

What affects risk of microshock induced ventricular arrhytmias

Answer 7

-site of stimuation
-Propotrional to the area stimulates
-increases the longer current passes

Question 8

Risk limits for microshocks

Answer 8

unlikely to cause harm below 44uA
Near the myocardium 100uA can cause dysrhytmia

Question 9

What equipment might predispose to microshock?

Answer 9

Saline filled (potentially conductive) CVC, pacing wires or oesophageal doppler probes.

Question 10

Type B electrical equipment permissable current leak (mA)

Answer 10

T1- <0.01 NC, <0.5 SFC
T2- <0.1 NC, <0.1 SFC

Question 11

What is different about type BF equipment?

Answer 11

Has an isolated floating circuit so suitable for patient connection

Question 12

What is type CF equipment?

Answer 12

high degree of protection against shock, so is suitable for direct cardiac connection.

Question 13

Maximum leakage currents for CF equipment?

Answer 13

NC <0.01 SFC <0.05 mA

Question 14

how does a floating circuit work?

Answer 14

separated from the mains supply by an isolating ttansformer- isolated from the substation circuit so cannot receive a shock

Question 15

How does a circuit breaker work

Answer 15

electromechanical devices disconnect the power supply from a piece of faulty electrical equipment when current flows down the earth wire

Question 16

what is the no let go threshold

Answer 16

15mA

Question 17

WHat rating is a typical medical infusion pump?

Answer 17

CF- as might be connected to a colum of saline all the way to the RA

Question 18

Why do you have to apply ground plate well in monopolar diathermy

Answer 18

otherwise smaller surface area -> increaed current density that can cause burns

Question 19

Unwanted effects of mono diathermy

Answer 19

affect medical equipment, burns, cardiac arrhythmias

Question 20

Power used in monopolar diathermy?

Answer 20

100-200 watts

Question 21

HOw much power does bipolar diathermy use?

Answer 21

<100 watts

Question 22

Microscopic effects of diathermy

Answer 22

Coagulation
Dessication

Question 23

Macroscopic effects of diathermy

Answer 23

Vapourisation
Tissue destruction

Question 24

Settings needed for cutting

Answer 24

Continuous high frequency (400KHz), low voltage (400V), High power

Question 25

settings needed for coag

Answer 25

intermittent current (arond 10% of time) with lower (200-400) frquency and higher (up to 9kV) voltages. lower powers
gives tissue time to cool

Question 26

how is monopolar diathermy protedcted from electrocuting patietns

Answer 26

isolating capacitor in the earth wire
High resistance to low frequecy currents (ie mains)
Low resistance to high frequency currents (diathermy)