ELECTRICAL SAFETY ForMEDICAL EQUIPMENT By Ismail Yusof
Electrical Safety – Medical EquipmentContents: 1 Various Test Equipment used in Biomedical Engineering 2 Introduction to Electrical Safety 3 Electricity - Physiological Effects 4 General Electrical Safety 5 Electricity – Leakage Current 6 Electrical Equipment – Classes and Types 7 Electrical Safety Tests
INTRODUCTION TO VARIOUS TESTEQUIPMENT USED IN BIOMEDICAL ENGINEERING
Workshop Tool & EquipmentToolkit for general repair
Workshop Tool & EquipmentInsulation and Resistance Measuring Instrument, 1000 V, Digital
Workshop Tool & EquipmentSoldering Stationwith temperature controller
Workshop Tool & Equipment Analog MultimeterDigital Multimeter
SAFETY TESTERSSafety Check – Electrical Safety Tests (IEC 601) – The basic purpose of safety testing in medical electrical equipment is to be sure that a device is safe for the patient and user. Such as: • Grounding resistance of portable medical equipment measured between equipment chassis and ground pin of power plug shall not exceed 0.50 ohms.
Biomedical Engineer-definition• Biomedical Engineers assist in struggle against illness and disease by providing support for materials and tools that can be utilized for diagnosis and treatment by health care professionals.• Biomedical Engineer have achieved this position by assuming responsibility for managing the safe use of medical equipment within the hospital environment
A Historical Perspective• Engineer’s first enter to clinical scene : late 1960s in response to concerns about electrical safety of hospital patient• Ralph Nader (consumer activist) : “at the very least, 1200 Americans are electrocuted annually during routine diagnostic and therapeutic procedures in hospitals” Ladies Home Journal, April 24, 1970• Raise the level of concern about safe use of medical device
A Historical Perspective• Overnight growth of a new industry : hospital electrical safety• Joint Commission on the Accreditation of Hospital : “hospital must inspect all equipment used on or near a patient for electrical safety at least every 6 months”• Hospital administrator’s options – Paying medical device manufacturer – Service contracting – In-house staff
Safety Issue• In USA, about 10,000 device-related patient injuries each year• Most injuries are attributable to improper use of a device as a result of inadequate training and lack of experience• Medical personnel rarely read user manuals until a problem occurred• “Everything that can go wrong eventually will go wrong” Murphy’s law
Electrical Shock• Electric Shock : unwanted or unnecessary physiological response to current.• Three phenomena : – (1) electrical stimulation of excitable tissue (nerve & muscle) – (2) resistive heating of tissue, and – (3) electrochemical burns and tissue damage
Electrical Safety• Electric Safety is the best possible limitation of hazardous electrical Macro – and/or Microshocks, sustained by patients, as well as explosion, fire or damage to equipments and buildings.
Single Phase Power Supply• The application of the safety testing on this training will only apply to the Single Phase ( 3 wires ) 100 to 240 Volt power supply.• Any medical equipment use either 3 or 2 pins plug which connected to the wall socket shall follow this electrical safety procedure.
The IEC 601.1 Standard Several standard serve as ruling authority in determine how medical equipment are to be tested such UL, CSA, CE, TUV … The International Electro Technical Commission’s IEC 601-1 standard is accepted and implemented around the world. All this explanation will be based on IEC 601-1 Standard
Medical Electrical Equipment Medical Electrical Equipment provided with no more than one connection to a particular supply mains and intended to;1. Diagnose the patient,2. Treat the patient,3. Monitor the patient under medical supervision,4. Makes physical or electrical contact with the patient ,5. Transfers energy to or from the patient and/or detects such energy transfer to or from patient. The equipment includes those accessories as defined by the manufacturer which are necessary to enable the normal use of the equipment.
Safety of Medical Equipment The purpose of safety testing medical electronic equipment is to ensure that a device is safe from electrical hazards to patients, maintenance personnels and users. Electric shock are caused by electricity flowing through the body after touching a damaged electrical device and results muscle spasms, burns, cardiac and respiratory arrest and Ventricular Fibrillation
Electrical Safety• Electric safety in hospital is a shared responsibility between several parties, in addition to the physician, including: • The nurses • All engineers (electrical, biomedical, facility, etc) • Manufacturers • The hospital
Electrical Safety – Critical Points• The electrical installation, no matter how safe, is only part of the safety requirements.• Plugs and cords must be checked and rejected if defective.• Only devices tested for safety should be used.• Electrical compatibility of the entire electrical system must be tested regularly.• Patients leads must be attached and connected properly.• Radio-frequency devices (including mobile telephones) must be excluded.
Basic Safety Basic safety should be performed on line powered before installation and after every repairs are; – Ground wire integrity ( Resistance ) – Ground wire leakage The basic electrical characteristic usually cause the most leakage currents in modern equipment is Capacitive Reactance Coupling in power cord. The typical range of human body resistance with the skin intact is 500 Ohm to 1,000 Ohm. The “let go” current of a shock is 14 mA in most people.
Why Electrical Safety? Electrical safety NOT dependent on voltage but on Leakage Current. At low voltage, leakage current flow through body may be fatal to us. Patient may connected to several device simultaneously . (ICU.) Patient may connected conductively with electronic circuit. (ECG.) Contact directly to internal tissue. ( natural orifices or break in the skin.)
Electricity - Physiological EffectsBurnsWhen an electric current passes throughany substance having electricalresistance, heat is produced. The amountof heat depends on the power-dissipated(I2R or VI). Whether or not the heatproduces a burn depends on the currentdensity.
Electricity - Physiological EffectsMuscle Cramps When an electrical stimulus is applied to a motor nerve or muscle, the muscle does exactly what it is designed to do in the presence of such a stimulus i.e. it contracts. The prolonged involuntary contraction of muscles (tetanus) caused by external electrical stimulus is responsible for the phenomenon where a person who is holding an electrically live object can be unable to let go.
A muscle cramp is a painful, involuntarymuscle contraction.
Electricity - Physiological EffectsRespiratory Arrest The muscles between the ribs (intercostal muscles) need to repeatedly contract and relax in order in order to facilitate breathing. Prolonged tetanus of these muscles can therefore prevent breathing.
Electricity - Physiological EffectsCardiac Arrest The heart is a muscular organ which needs to able to contract and relax repetitively in order to perform its function as a pump for the blood. Tetanus of the heart musculature will prevent the pumping process.
Electricity - Physiological EffectsVentricular Fibrillation The ventricles of the heart are the chambers responsible for pumping blood out of the heart. When the heart is in ventricular fibrillation, the musculature of the ventricles undergoes irregular, uncoordinated twitching resulting in no net blood flow. The condition proves fatal if not corrected in a very short space of time.
Ventricular fibrillation (VF) is a deadly arrhythmia.In VF, the electrical signals that trigger theheartbeat become very fast and chaotic in thelower chambers of the heart. The heart no longercan pump blood to the brain or body.
Electricity - Physiological EffectsElectrolysis The movement of ions of opposite polarities in opposite directions through a medium is called electrolysis and can be made to occur be made to occur by passing DC currents through body tissues or fluids.
Important Susceptibility Parameters For dog: 20A, human : 80~600 A Safety limit : 10 AEffect of entry point on current distribution
Macroshock HazardsMacroshock is the mostcommon type of shockreceived and occurs when thehuman body becomes aconductor of electric currentpassing by means other thandirectly through the heart.
Microshock HazardsElectrically conducting devicesunintentionally make directcontact with heart muscles,ventricular fibrillation may beinduced by minute current (e.g.200 uA) well below the thresholdof feeling.
Electricity - Leakage CurrentsLeakage Currents Current that is not functional. The following leakage currents are defined: Earth Leakage Current , Enclosure Leakage Current , and Patient Leakage Current . Earth Enclosure Patient Leakage Leakage Leakage Current Current Current
Electricity - Leakage CurrentsCauses of leakage currents If any conductor is raised to a potential above earth potential, then some current is bound to flow from that conductor to earth. This is true even of conductors that are well insulated from earth, since there is no such thing as perfect insulation or infinite resistance. The amount of current that flows depends on: • The voltage on the conductor • The capacitive reactance between the conductor and earth • The resistance between the conductor and earth
Leakage CurrentLeakage current flows betweenpower supply wires and earthground within the rated value. Incase of the multiple operation,however, the total leakage currentwill be the sum of the leakagecurrent flows from each powersupply.
Electricity - Leakage CurrentsEarth leakage current Earth leakage current is the current which normally flows in the earth conductor of a protectively earthed piece of equipment.
Electricity – Enclosure Leakage CurrentsEnclosure leakage current Enclosure leakage current is described as the current that flows from an exposed conductive part of the conductor to earth through a conductor other than the protective earth conductor.
Electricity – Patient Auxiliary CurrentPatient auxiliary currentThe patient auxiliary current is defined as the current which normally flows between parts of the applied part through the patient which is not intended to produce a physiological effect.
Electricity – Class and Types of EquipmentClasses of Equipment All electrical equipment is categorized into classes according to the method of protection against electric shock that is used.Types of Equipment The degree of protection for medical electrical equipment is defined by the type designation.
Electricity – Class of EquipmentClasses of EquipmentAll electrical equipment is categorized intoclasses according to the method of protectionagainst electric shock that is used. CLASS I CLASS II CLASS III
Electricity – Class of EquipmentClass I equipment Class 1 equipment has a protective earth. The basic means of protection is the insulation between live parts and exposed conductive parts such as the metal enclosure. In the event of a fault which would otherwise cause an exposed conductive part to become live, the supplementary protection (i.e. protective earth) comes into effect.
Electricity – Class of EquipmentClass II equipment The method of protection against electric shock in the case of class II equipment is either double insulation or reinforced insulation. In double insulated equipment the basic protection is afforded by the first layer of insulation. If basic protection fails then supplementary protection is afforded by a second layer of insulation preventing contact with live parts.
Electricity – Class of EquipmentClass II equipment The symbol for class II equipment is 2 concentric squares indicating double insulation as shown below.
Electricity – Class of EquipmentClass III equipment Class III equipment is defined as that in which protection against electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are present.SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V dc.
Electricity – Types of EquipmentTypes of EquipmentThe degree of protection for medicalelectrical equipment is defined by the typedesignation. Type B Type BF Type CF
Electricity – Types of EquipmentType Symbol Definition B Equipment providing a particular degree of protection against electric shock, particularly regarding allowable leakage currents and reliability of the protective earth connection (if present).BF As type B but with isolated or floating (F type) applied part or partsCF Equipment providing a higher degree of protection against electric shock than type BF, particularly with regard to allowable leakage currents, and having floating applied parts.
Electrical Safety TestsNormal Condition A basic principle behind the philosophy of electrical safety is that in the event of a single abnormal external condition arising or of the failure of a single means of protection against a hazard, no safety hazard should arise.
Electrical Safety TestsSingle Fault Condition Condition in which a single means of electrical safety protection is defective or an abnormal condition is present. Examples of a single fault condition would be interruption of the ground conductor on a Class I equipment or opening of the neutral supply conductor to the equipment.
Electrical Safety ReviewElectrical Safety and the Patients Depends on Three Things: -• An alert, caring, knowledgeable person• Properly maintained, and applied equipment• Proper grounding or double insulation of line- powered equipment
Electrical Safety ReviewReport, tag, and do not use equipment with:• Frayed wires or cracked insulation• Damaged plugs or missing ground prongs
Electrical Safety ReviewReport, tag, and do not use receptacles with:• Only two slots• Missing cover plates• Loose mountings• Weak gripping force
Electrical Safety ReviewInspections of Equipment: -• Check of Strain-Relief
Electrical Safety ReviewAvoid:• Using cheaters (three-prong adapters)• Using extension cords• Placing liquids on electrical equipment• Pulling plugs out of receptacles by the cord• Rolling equipment over power cords• Using defective equipment or receptacles• Using equipment that sparks, smokes, or shocks
Electrical Safety ReviewBe sure that users know how to use equipment properly. Also be sure to:• Check that line-powered equipment has three- wire grounding cords, unless device is double insulated• Ask for help and instruction when needed• Report defective equipment and receptacles
Electrical Safety Review Always use your common sense Do not end up like this person!