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

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.

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.

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

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.

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

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

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

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

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

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

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

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.

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

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

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

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

Micro- vs. Macroshock Hazards Points of Entry

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.

The ‘Liverpool’ Safety Tester 1973

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

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

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.

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

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

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

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.

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.

What’s the problem?

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

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

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

Summary Your responsibility to take care of yourself and others