2 Electrical safety Electrical Safety Testing Procedure Content Physiological Effects of ElectricityBasic Electrical TheoryHuman susceptibility to electric shockCodes and Standards.Equipment DesignElectrical Safety Testing ProcedureSpecific Hazards & Personal Safety
3 IntroductionEveryone should have some knowledge of the every day source of energy known as electricityEveryone should also know about the potential hazards & how to avoid themIt 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 products40,000 residential electrical fires occur annually.More than $2 billion is lost on property damage.
5 Our main objectives are to understand the possible electricalhazards and fault scenarios andlearn how to improve deigns ofmedical instruments.
6 CautionsIt would appear that the young & old are more prone to electric shockPerhaps this is due in the first instance due to a lack of appreciation of the dangersIt 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 MusclesMuscles control all the body movementsIncluding & importantly those that keep us alive - Breathing and HeartThe 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 carelessnessMain effects:Neuromuscular (stimulation of nerves & muscles)-- Loss of muscle controlSpasms & Involuntary movementInability to let goBurns
9 External current through the body external & internal Muscle crampsRespiratory arrestVentricular fibrillation(50 microamps can interfere with cardiac cycle)Electrolysis
10 Basic Electrical Theory Voltage [driving force] causes current [e - ] to flowAC / DC - from safety perspective - negligible differenceSingle Phase / Three Phase.Circuit / loop is necessary for current to flowa start point - a route - an end point
11 Voltage, Current and Resistance Voltage increases => Current increasesResistance decreases => Current increasesVoltage = Current / Resistance Ohms Law
12 The complete circuit necessary for current to flow A complete Circuit or loop isnecessary for current to flow
13 A complete circuit complete Circuit or loop is necessary for current to flowCurrent takes the path of least resistance
15 Hospital SafetyNow days the patient environment contains a large amount of medical equipment providing various functions to aid the care of patientsMany items of medical equipment may be connected to the patient at the same timeThe hazards are greater due to the involvement of sick peoplePeople 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 CurrentFerequencyBody and skin ResistancesDurationBody weightPoint- of- entry
17 Physiological Response to Electricity Threshold of Perception mALet - go – Current mAMuscles Contraction mAPain and respiratoryParalysis mAVentricular Fibrilation mABurns A
26 Safety StandardsModern medical equipment is now manufactured in such a way that the risks of electric shock are minimalModern understanding of electrical equipment & causes of electric shock has brought about greater safety awareness.
33 Hazards Water & electricity Overloaded circuits Damaged insulation Misuse of extension cablesExposed wiringPower cords in walkways
34 Precautions If equipment gets wet, get it checked If cabling damaged /exposed, get it checkedDo not replace fuses on medical equipmentIf 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 circuitUse appropriate fuse size/ratingFuses 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 useEnsure there is no damage to mains plugEnsure there is no damage to mains cableDo understand how to use the equipment safely
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.
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 SummaryYour responsibilityto take care ofyourself and others