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Electrical safety
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
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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
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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.
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• Our main objectives are to
• understand the possible electrical
hazards and fault scenarios and
• learn how to improve deigns of
medical instruments.
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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
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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
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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
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External current through the body
• external & internal Muscle cramps
• Respiratory arrest
• Ventricular fibrillation
(50 microamps can interfere with cardiac cycle)
• Electrolysis
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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
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Voltage, Current and Resistance
• Voltage increases => Current increases • Resistance decreases => Current increases
Voltage = Current / Resistance - Ohms Law
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The complete circuit A complete Circuit or loop is
necessary for current to flow
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A complete circuit complete Circuit or loop
is necessary for current to flow
Current takes the path of least resistance
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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
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Human susceptibility to electric shock
• Current• Ferequency• Body and skin Resistances• Duration• Body weight• Point- of- entry
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Physiological Response to Electricity• Threshold of Perception 1 mA• Let - go – Current 5 mA• Muscles Contraction 10 mA• Pain and respiratoryParalysis 50 mA • Ventricular Fibrilation 100-300 mA• Burns 1 A
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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 = 10 -6 s• Nerve communication T =10-5
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Duration/Body Weight Susceptibility
• Strength-duration curve is a very important plot, applicable to shocks, pacemaker/defibrillator type devices, etc.
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Micro- vs. Macroshock Hazards Points of Entry
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Safety Standards
• Modern medical equipment is now manufactured in such a way that the risks of electric shock are minimal
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The ‘Liverpool’ Safety Tester 1973
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Hazards• Water & electricity• Overloaded circuits• Damaged insulation• Misuse of extension cables• Exposed wiring• Power cords in walkways
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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
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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
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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
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Electrical cables & plugs Mains cable
– Brown Live - power
– Blue Neutral – Green/yellow Earth
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Electrical cables & plugs
Mains cable
– Brown Live power
– Blue Neutral – Green/yellow Earth
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Can you spot the problems?
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What’s the problem?
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Summary
Your responsibility to take care of
yourself and others
