Electrical Safety
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.
- Equipment Classification
- Protective Devices
- Area Classification
- Other Electrical Issues
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.
Leakage Current
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
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
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.
EQUIPMENT CLASSIFICATIONS
There are several methods of providing protection for operators and patients from electrical faults and harmful leakage current.
Class I
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
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:
Defibrillator-Proof
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
PROTECTIVE DEVICES
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.
Residual Current Devices (RCD)
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
- Lamp indicates supply is no longer available
- Disconnect all equipment from the supply
- Operate the reset button or lever on the supply panel and the 'Supply Available' lamp should illuminate. If not, contact Biomedical Engineering.
- Connect an item of equipment. If the RCD trips again, then this is the faulty item and should be labelled and sent to Biomedical Engineering.
- If the RCD does not trip, continue connecting equipment until the RCD trips. The last piece of equipment connected to the supply is most likely to be faulty as it will have caused the RCD to trip. Remove the faulty item from service, label it and send to Biomedical Engineering as mentioned above.
Line Isolation overload Monitors (LIMs)
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
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.
AREA CLASSIFICATIONS
Body Protected Area
- These areas are designed for procedures in which patients are connected to equipment that lowers the natural resistance of the skin. Applied parts such as electrode gels, conductive fluids entering the patient, metal needles and catheters provide an easy pathway for current to flow.
- The main occurrence of injury from Body-Type procedures is from high current levels causing electric shock. A direct connection to the patient's heart is not present so the risk of 'Microelectrocution' - fibrillation from minute current levels - is reduced.
- Residual Current Devices (RCD) or Isolation Transformers and Line Isolation Monitors (LIMÃs), are used in Body Protected areas to provide protection against electrocution from high leakage currents. Body-Protected Areas are identified with this sign.
- Where the procedure involves placing an electrical conductor within or near the heart, protection against fibrillation induced from small leakage currents is required. Electrical conductors used in these procedures include cardiac pacing electrodes, intracardiac ECG electrodes and intracardiac catheters.
- Equipotential earthing in conjunction with RCD's or LIM's provides protection against microelectrocution in Cardiac-Type procedures.
- Fault currents are reduced to magnitudes that are unlikely to induce fibrillation. Used in conjunction with RCD's or LIM's, the magnitude and duration of any fault currents sourced from equipment are limited.
- Cardiac-Protected Areas are identified with this sign.
Other electrical issues
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.
Extension leads
Approved extension leads (AS 3760, 1996) may be used in some areas within the hospital but MUST NOT BE USED IN PATIENT AREAS. All electrical extension leads must be tagged with an Engineering Department maintenance tag, and require a yearly safety inspection and test, via the Engineering Department.
Double adapters
Double adapters may cause overloading or equipment earthing problems and are not to be used in WCH
Mains extension device
The only mains extension device that is to be used in "Patient care areas" is the 4-way or 8-way portable Core Balance Unit.
The Biomedical Engineering Department must approve all units prior to use. These units contain a safety switch and can detect excessive leakage current and disconnect the power in the event of a hazardous situation.
Care must be exercised in the use of a portable Core Balance Unit. It should be located off the floor and in a position that will protect it from physical abuse and possible entry of fluids. These devices are expensive and easily damaged. The device must be sent to Biomedical Engineering every 6 months for safety testing.
Power boards
Approved multiple-outlet power boards can be used across RCH but must not be used in patient care areas, except areas approved by the Biomedical Engineering Department.
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.
Installation of additional power points
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 Project Initiation Request should be submitted to the Engineering Department for the installation of additional power points.
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