2. Electrical safety Electrical Safety Testing Procedure Content
Physiological Effects of Electricity
Basic Electrical Theory
Human susceptibility to electric shock
Codes and Standards.
Equipment Design
Electrical Safety Testing Procedure
Specific Hazards & Personal Safety

3. Introduction
Everyone should have some knowledge of the every day source of energy known as electricity
Everyone should also know about the potential hazards & how to avoid them
It would make sense that everyone, not only people responsible for Electrical Safety, understands electricity & the potential dangers that it presents.
We all use electricity every day, both at home & work, so some knowledge & appreciation is useful.

4. Are you aware Electrocutions are the 5th leading
cause of Accidental death in the U.S.
More than 700 people lose their lives every year because of accidents associated with electricity and electrical products
40,000 residential electrical fires occur annually.
More than $2 billion is lost on property damage.

5. Our main objectives are to
understand the possible electrical
hazards and fault scenarios and
learn how to improve deigns of
medical instruments.

6. Cautions
It would appear that the young & old are more prone to electric shock
Perhaps this is due in the first instance due to a lack of appreciation of the dangers
It is often the case that people who are young, because they don't know any better, will receive an electric shock from tampering with electrical apparatus.
Whilst people who are old take to many risks & forget the dangers, of which they were once aware.

7. Electricity in the body
Muscles
Muscles control all the body movements
Including & importantly those that keep us alive - Breathing and Heart
The brain controls voluntary muscles using Current pulses along nerves

8. External current through the body
Many people have received an electric shock at some stage or other through carelessness
Main effects:
Neuromuscular (stimulation of nerves & muscles)
-- Loss of muscle control
Spasms & Involuntary movement
Inability to let go
Burns

9. External current through the body
external & internal Muscle cramps
Respiratory arrest
Ventricular fibrillation
(50 microamps can interfere with cardiac cycle)
Electrolysis

10. Basic Electrical Theory
Voltage [driving force] causes current [e - ] to flow
AC / DC - from safety perspective - negligible difference
Single Phase / Three Phase.
Circuit / loop is necessary for current to flow
a start point - a route - an end point

11. Voltage, Current and Resistance
Voltage increases => Current increases
Resistance decreases => Current increases
Voltage = Current / Resistance Ohms Law

12. The complete circuit necessary for current to flow
A complete Circuit or loop is
necessary for current to flow

13. A complete circuit complete Circuit or loop
is necessary for current to flow
Current takes the path of least resistance

15. Hospital Safety
Now days the patient environment contains a large amount of medical equipment providing various functions to aid the care of patients
Many items of medical equipment may be connected to the patient at the same time
The hazards are greater due to the involvement of sick people
People in hospital are in a weakened physiological state due to their reason for hospitalisation. This means that they are more susceptible to any electrical exposure, that a normal fit, healthy person may withstand.

16. Human susceptibility to electric shock
Current
Ferequency
Body and skin Resistances
Duration
Body weight
Point- of- entry

17. Physiological Response to Electricity
Threshold of Perception mA
Let - go – Current mA
Muscles Contraction mA
Pain and respiratoryParalysis mA
Ventricular Fibrilation mA
Burns A

19. Current vs. Frequency Difference in DC vs AC shocks
Very high threshold/low sensitivity at high frequencies used in many medical applications
Diathermy F = 27,12 MHz
T = s
Nerve communication T =10-5

21. Duration/Body Weight Susceptibility
Strength-duration curve is a very important plot, applicable to shocks, pacemaker/defibrillator type devices, etc.

23. Micro- vs. Macroshock Hazards Points of Entry

26. Safety Standards
Modern medical equipment is now manufactured in such a way that the risks of electric shock are minimal
Modern understanding of electrical equipment & causes of electric shock has brought about greater safety awareness.

29. The ‘Liverpool’ Safety Tester 1973

33. Hazards Water & electricity Overloaded circuits Damaged insulation
Misuse of extension cables
Exposed wiring
Power cords in walkways

34. Precautions If equipment gets wet, get it checked
If cabling damaged /exposed, get it checked
Do not replace fuses on medical equipment
If equipment damaged, get it checked

35. Fuses/Circuit Breakers
The Fuse is very thin piece of wire.
The wire has a quite low melting point. As current flows through the wire it heats up.
If too large a current flows it melts, thus breaking the circuit
Use appropriate fuse size/rating
Fuses blow due to the heating effect of electrical current. Excess current will cause more heat then the given wire in the fuse can take, causing an overheating of the wire & a resultant break in the fuse circuit.

36. How Can Users Assist? Do NOT carry out any repairs yourself
Check equipment for damage before use
Ensure there is no damage to mains plug
Ensure there is no damage to mains cable
Do understand how to use the equipment safely

37. Electrical cables & plugs
Mains cable
Brown Live - power
Blue Neutral
Green/yellow Earth

38. Electrical cables & plugs
Mains cable
Brown Live power
Blue Neutral
Green/yellow Earth L N

39. Can you spot the problems?
Fuse wire has been attached to a blown fuse (by somebody with a degree of knowledge) to make a piece of equipment work again.

40. Blown fuses have been “repaired” by covering with metal foil – at what value of current will the fuse blow !!
Mains cable has been extended by twisting wires together & then covering with tape – not satisfactory.

41. What’s the problem?

43. Bare insulation showing the individual mains cables.
It is likely that the mains cable has been pulled out of the equipment – this may result in the cable coming away from internal connection points – could be very dangerous

44. Looking closely at the mains switch, somebody has hard wired one of the switch contacts to make a permenant connection (they were obviously clever enough to deduce that one of the switch contacts was not operating correctly – but the switch should have been replaced).
This equipment was in use in a patients home – be wary of “home use” equipment

45. Very bad wiring of mains plug – stray strands (could actually bypass the fuse, or at the least arc inside the plug)

46. Summary
Your responsibility
to take care of
yourself and others