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:
 

Effective equipotential grounding is the bonding of all conductive surfaces in the room together and to earth. It is crucial to keep all conductive surfaces at the same potential. A level ground plane prevents a different voltage potential between all the conducting surfaces in the room, avoiding current flow from one object to another. Also a controlled low impedance path to ground is needed for any fault current that may develop in the patient environment.