In this section
Electrical safety is very important in hospitals as patients may be undergoing a diagnostic or treatment procedure where the protective effect of dry skin is reduced. Also patients may be unattended, unconscious or anaesthetised and may not respond normally to an electric current. Further, electrically conductive solutions, such as blood and saline, are often present in patient treatment areas and may drip or spill on electrical equipment.
Injuries received from electric current are dependent on the magnitude of current, the pathway that it takes through the body and the time for which it flows.
The nature of electricity flowing through a circuit is analogous to blood flowing through the circulatory system within the human body. In this analogy the source of energy is represented by the heart, and the blood flowing through arteries and veins is analagous to current flowing through the conductors and other components of the electric circuit.
The application of an electric potential to an electric circuit generates a flow of current through conductive pathways. This is analogous to the changes in blood pressure caused by contraction of cardiac muscle that causes blood to flow into the circulatory system. For electric current to flow there must be a continuous pathway from the source of potential through electrical components and back to the source.
Electrical components and systems are encased in non conducting insulation, to ensure that the electric current is contained and follows the intended pathways. If the insulation deteriorates or breaks down, current will leak through the insulation barrier and flow to earth. This may be through the protective earth conductor or through the operator.
Medical equipment and clinical areas are fitted with a number of protective devices to protect the patient and operator from harmful leakage currents.
Extension leads are not permitted in clinical areas of RCH organisations. They may cause high earth resistance and excessive earth leakage current. An extension lead can allow equipment to be powered from areas other than the relevant protected treatment area. The power from the other area may not be protected to the same level as the power in the treatment area.
As the connection between the extension lead and the equipment mains cable is often on the floor there is a high danger from fluid spills, tripping and damage to the mains cable by trolleys when an extension lead is used.
Double adaptors must not be used in RCH organisations. They may not sit securely in a wall outlet, may not be able to provide adequate earth protection and may cause overloading, overheating, fire or loss of electrical supply.
There are several methods of providing protection for operators and patients from electrical faults and harmful leakage current.
Class I equipment is fitted with a three core mains cable containing a protective earth wire. Exposed metal parts on class I equipment are connected to this earth wire.
Should a fault develop inside the equipment and the exposed metal comes into contact with the mains, the earthing conductor will conduct the fault current to ground. Regular testing procedures ensure that earthing conductors are intact, as the integrity of the earth wire is of vital importance.
Class II equipment is enclosed within a double insulated case and does not require earthing conductors. Class II equipment is usually fitted with a 2-pin mains plug. An internal electrical fault is unlikely to be hazardous as the double insulation prevents any external parts from becoming alive. Class II or double insulated equipment can be identified by the class II symbol on the cabinet.
Class II Symbol:
Some medical equipment within the hospital is classified as defibrillator proof. When a defibrillator is discharged through a patient connected to defibrillator proof equipment, the equipment will not be damaged by the defibrillator's energy. Defibrillator proof equipment can remain connected to the patient during defibrillation. It is identified by one of the following symbols.
Defibrillator proof symbols.
Body protected Cardiac protected
Most patient care areas in the hospital are fitted with protective devices. These devices are regularly tested, in accordance with the relevant guidelines published by Standards Australia. The level of protection provided is dependent upon the device and the area in which it is located.
RCD's (safety switches) are used in patient treatment areas to monitor and protect the mains supply. RCD's sense leakage currents flowing to earth from the equipment. If a significant leakage current flows, the RCD will detect it and shut off the power supplied to the equipment within 40 milliseconds. Hospital RCD's are more sensitive than those fitted in homes. A hospital RCD will trip at 10 milliamperes leakage current.
Power outlets supplied through an RCD have a 'Supply Available' lamp. The lamp will extinguish when the RCD trips due to excessive leakage current.
Resetting a RCD
In critical life support applications where loss of power supply cannot be tolerated, special power outlets powered by isolation transformers are installed.
Line Isolation Monitors are installed to continually monitor electrical leakage in the power supply system. If an electrical fault develops in a medical device connected to an isolated power outlet, the LIM will detect the leakage current. The LIM will alarm and indicate the level of leakage current, but will not shut off the electric supply.
The faulty equipment can be identified by un plugging one item of equipment at a time from the supply until the alarm stops sounding. Equipment that is not faulty may be reconnected. Faulty equipment should be appropriately labelled and sent to Biomedical Engineering for repair.
The LIM also monitors how much power is being used by the equpiment connected to it. If too much power is being used, the LIM will alarm and indicate that there is an overload. The power used must be reduced immediately by moving some equipment to another circuit as soon as possible until the alarm stops sounding. Failure to reduce the load on the LIM will result in the circuit breaker tripping and loss of power to the circuit.
Equipotential earthing is installed in rooms classified as 'Cardiac Protected' electrical areas. Equipotential earthing in treatment areas used for cardiac procedures is intended to minimise any voltage differences between earthed parts of equipment and any other exposed metal in the room.
This reduces the possibility of leakage currents that can cause microelectrocution when the patient comes into contact with multiple items of equipment, or if the patient happens to come into contact with metal items in the room whilr they are connected to a medical device.
All conductive metal in an equipotential area is connected to a common equipotential earth point with special heavy duty cable.
This policy aims to provide guidance to those who find that they need more electrical outlets than those available, or that the existing electrical outlets are inconveniently located.
As extension leads and multiple outlet power boards can introduce additional hazards into an area the following procedures should be observed.
Power boards must not be used in patient care areas.
Power boards may only be used for low power devices such as computers and printers in non clinical areas. Power boards should never be connected to another power board.
The power boards must have overload protection, be fitted with internal safety shutters that protect unused outlets and be fitted with an on/off switch for each outlet. They must be tested and tagged by Spotless services prior to use.
All of the above mentioned devices are intended to overcome a temporary inadequacy in the electrical installation. If a Department/Unit is likely to have a long term need for such mains extension devices a Minor Works Request should be submitted to the Spotless Facilities Management Department for the installation of additional power points.