Download Electrical Safety

ELECTRICAL SAFETY
Introduction
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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
Effects Of Electricity
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Many people have received an electric shock
at some stage or other through carelessness
Main effects:
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Neuromuscular (stimulation of nerves & muscles)
Heating (burns)
Electrolysis (decomposition/chemical change)
Heart (50 microamps can interfere with cardiac
cycle)
Cautions
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It is necessary to respect electricity & it’s
hazards
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
And in the second instance due to over
familiarity
Cautions
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Electrocution claims the lives of a few hundred
people each year, mostly involving domestic
electrical equipment
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The primary variable for determining the severity of electric
shock is the electric current which passes through the
body. This current is of course dependent upon the voltage
and the resistance of the path it follows through the body.
An approximate general framework for shock effects is as
follows:
Electric Current
(1 second contact)
1 mA

10-20 mA
sustained
100-300 mA
Physiological Effect
Threshold of feeling, tingling sensation.
"Can't let go!" current - onset of
muscular contraction
Ventricular fibrillation, fatal if continued
Shock Physiological Effects
Electric
Current
(1 second
contact)
1 mA
5 mA
10-20 mA
100-300
mA
6A
Physiological Effect
Threshold of feeling, tingling sensation.
Accepted as maximum harmless current
Beginning of sustained muscular contraction
("Can't let go" current.)
Ventricular fibrillation, fatal if continued.
Respiratory function continues.
Sustained ventricular contraction followed by
normal heart rythmn. (defibrillation). Temporary
respiratory paralysis and possibly burns.
Hospital Safety
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Electrical equipment is used in Hospitals
therefore the same risks are present, but the
hazards are greater due to the involvement of
sick people
Hospital Safety
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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
Hospital Safety
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Human susceptibility to electric shock varies
from individual to to individual & depends on a
number of factors:
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The patients general state of health
The position of any electrodes on the patient
The dampness of the patients skin
Safety Standards
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Modern medical equipment is now
manufactured in such a way that the risks of
electric shock are minimal
Shock
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Micro shock –Effect of current applied to the
heart
Macro shock- Effect of current applied through
the surface contacts
Safety Standards
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Equipment is designed & built to comply with
safety standards
This lays down constructional guidelines for
medical equipment which influence the safety
of the equipment
Safety Testing To BS EN 60601-1
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Medical electrical equipment is divided into two
classes
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Class 1
Class 2
And, three types
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Type B
Type BF
Type CF
Class 1
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Is equipment in which protection against
electric shock does not rely on basic insulation
only, but which includes an additional safety
precaution, in that means are provided for the
connection of the equipment to the protective
earth conductor in the fixed wiring installation
in such a way that accessible metal parts
cannot become live in the event of a failure of
the basic insulation
Class 2
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Is equipment in which protection against
electric shock does not rely on basic insulation
only, but in which additional safety precautions
such as double insulation or reinforced
insulation are provided, there being no
provision for protective earthing or reliance on
installation conditions
Type B
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Is equipment providing a particular degree of
protection against electric shock, particularly
regarding:
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Allowable leakage current
Reliability of the protective earth connection if
present
Type BF
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Is type B equipment with an F type applied part
(applied part isolated from all other parts of the
equipment to such a degree that the patient
leakage current allowable in single fault
condition is not exceeded when a voltage
equal to 1.1 times the highest rated mains
voltage is applied between the applied part &
earth)
Type CF
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Is equipment providing a degree of protection
higher than that for type BF equipment against
electric shock particularly regarding allowable
leakage currents, & having a F type applied
part
Symbols on Medical Devices
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Class II equipment
Type B equipment
Type BF equipment
Type CF equipment
Symbols on Medical Devices
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Protective Earth
Earth (ground)
Attention, consult accompanying documents
Dangerous voltage
Common Safety Test Problems
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Most problems appear on the mains part
(particularly detachable mains leads)
Extra vigilance is therefore required by users
Electrical Safety Testing
Electrical Safety Testing Procedure
Visual Inspection
Earth Resistance
Insulation
Leakage Current
Earth Leakage
Current
Touch Current
Patient Leakage
Current
Photos
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Can you spot the problems?
Electrical Safety Testing
Leakage Current Test
Current
Limit
Earth
Leakage
Touch
Current
Normal
Touch
Current
Patient
Leakage
Normal
Patient
Leakage
5 mA
100 μA
500 μA
100 μA B, BF
10 μA CF
500 μA B, BF
50 μA CF
Fuses/Circuit Breakers
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Prevent overloading & fires
Stop the electrical current if it exceeds a safe
value
Fuse rating:
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Power = V I
transposing, I=P/V
Hazards
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Water & electricity
Overloaded circuits
Damaged insulation
Misuse of extension cables
Exposed wiring
Power cords in walkways
Precautions
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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
How Can Users Assist?
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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
Points To Remember
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Fuses are the weakest link
Avoid touching patients & equipment at the
same time, as a conductive path exists
Let common sense prevail
Safety First
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Remember do not end up like this person!