Need for Electrical Safety in Hospitals
The patients natural reactions to hazards are reduced or
switched off. The heart muscle is highly sensitive to electric
currents(currents > 10 uA). The insertion of catheters and the like into the
body may reduce the electrical resistance of the skin. Body functions are
temporarily or continuously supported or substituted by medical electrical
devices. Fire and explosion risks through the use of anaesthetics,
disinfectants or cleaning. Even small currents flowing through the human body
put the patients life and health at risk. The availability of the power supply
must be guaranteed, even under the fault conditions.
Harmful Effects of
Electricity:
1.Respiratory
Paralysis:
It causes involuntary contraction of respiratory muscles
severe enough to bring about asphyxiation. Respiratory arrest has been observed
at 18 to 22 mA.
2. Ventricular
Fibrillation:
The heart is susceptible to electric current in a special way
that makes some currents particularly dangerous. If the magnitude of the
current is sufficient to excite even only
a part of the heart muscle, then the normal propagation of electric
activity in the heart muscle is disrupted .The pumping action of the heart ceases
and death occurs within minutes. The cardiac rhythm is disorganized & is
called ventricular fibrillation and unfortunately it does not stop when the
current that triggered it is removed. This is the major cause of death due to
electrical shock. The thresh old of ventricular fibrillation for an average
sized human varies from about 75 to 400 mA.
3. Sustained Mycordial
contraction:
Due to high currents heart muscles contracts. In hospitals there
are general and critical care areas. In general care areas patients have only
incidental contact with electric devices while for critical areas patients are
intentionally exposed to electric device and insulation of centralized cardiac
conductors from conductive surfaces is required .In critical care areas all
exposed conductive surfaces in the vicinity of the patient must be grounded at
a single patient –grounding point. Also periodic testing for continuity between
the patient ground and all grounded surfaces is required.
Apart
from these there is always a risk of fire from disinfectants and anesthetics as
these are highly inflammable.
Solution to Electrical Safety Problems:
Isolated Power Systems:
Even installing a good separate grounding system for each
patient cannot prevent possible hazardous voltages that can result from ground
faults. A ground fault is a short circuit between the hot conductor and ground
that injects large currents into the grounding system.
We need to isolate all the power conductors from the ground. Isolation
of conductors is commonly achieved by isolation transformer. In an isolated
system such as this if a single ground fault from either conductor to ground
occurs,the system simply reverts to a normal grounded system. A second fault
from the other conductor to the ground is then require to get large currents in the ground.
A continuously operating Line Isolation Monitor (LIM) must be
used with isolation transformers to detect the occurrence of the first fault.
When the total hazard current exceeds 3.7 to 5 mA it causes red light and
sounds alarm.
Isolated power systems were originally introduced to prevent
sparks from corning into contact with flammable anesthetics such as either.
Equipotential Grounding: