medical electrical safety

ELECTRICAL SAFETY

MEDICAL EQUIPMENT

By

Ismail Yusof

For

Electrical Safety – Medical Equipment

Contents:

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 TEST

EQUIPMENT USED IN BIOMEDICAL

ENGINEERING

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Workshop Tool & Equipment

Toolkit for general repair

Insulation and Resistance Measuring Instrument, 1000 V, Digital


Soldering Station

with temperature controller


Digital MultimeterAnalog Multimeter


Electrical Safety Analyser

Test Instrument

Test Instrument

It measures delivered energy on its internal load.

The defibrillator pulse is stored and it can be viewed

via ECG output leads, paddles or scope output.

Test Instrument

Blood pressure simulator

that provides simulation

to test blood pressure monitors.

Test Instrument

The pulse oximeter testing method to simulate

the light absorption and arterial blood flow

of a human finger

Test Instrument

Power meter to service

the 1 MHz and 3 MHz therapy level

ultrasound generators.

Test Instrument

External pacemaker tester designed for

accurately testing all types of

external pacemaker.

Test Instrument

Test Instrument

Measure output power and RF leakage

ESU Analyser

Test Instrument

Infusion Pump Analyzer

Test Instrument

SAFETY TESTERS

Safety 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.

ELECTRICAL

SAFETY


• 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

Biomedical Engineer-definition

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

The 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 personnel's

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 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.

Basic 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.)

Why Electrical Safety?

Electricity - Physiological Effects

Burns

When an electric current passes through

any substance having electrical

resistance, heat is produced. The amount

of heat depends on the power-dissipated

(I2R or VI). Whether or not the heat

produces a burn depends on the current

density.


Muscle 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, involuntary muscle contraction.


Respiratory 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.

Respiratory Arrest


Cardiac 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.

Cardiac Arrest


Ventricular 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 the

heartbeat become very fast and chaotic in the

lower chambers of the heart. The heart no longer

can pump blood to the brain or body.


Electrolysis

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.

electrode(metal)

wire(metal)

electrode(metal)

wire(metal)

e-Charge carrier

TissueElectrolyte/Dielectric

cell

skin

ionsCharge carrier

Electricity Conduction Mechanism

Electrochemical Reactions

e-Charge carrier

Effect of entry point on current distribution

For dog: 20A, human : 80~600 A

Safety limit : 10 A

Important Susceptibility Parameters

Macroshock

Hazards

Macroshock is the most

common type of shock

received and occurs when the

human body becomes a

conductor of electric current

passing by means other than

directly through the heart.

Microshock

Hazards

Electrically conducting devices

unintentionally make direct

contact with heart muscles,

ventricular fibrillation may be

induced by minute current (e.g.

200 uA) well below the threshold

of feeling.

General Electrical Safety

Electricity - Leakage Currents

Leakage Currents

Current that is not functional. The following

leakage currents are defined: Earth Leakage

Current , Enclosure Leakage Current , and

Patient Leakage Current .

Earth

Leakage

Current

Enclosure

Leakage

Current

Patient

Leakage

Current


Causes 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

Current

Leakage current flows between

power supply wires and earth

ground within the rated value. In

case of the multiple operation,

however, the total leakage current

will be the sum of the leakage

current flows from each power

supply.


Earth leakage current

Earth leakage current is the current which

normally flows in the earth conductor of a

protectively earthed piece of equipment.

Enclosure 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 –

Enclosure Leakage Currents

Electricity –

Enclosure Leakage Currents

Patient leakage current

Patient leakage current is the leakage current that

flows through a patient connected to an applied

part or parts.

Electricity –

Patient Leakage Current

Electricity –


Patient auxiliary current

The 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 –

Patient Auxiliary Current

Electricity –


Classes 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 and Types of Equipment

Classes of Equipment

All electrical equipment is categorized into

classes according to the method of protection

against electric shock that is used.

Electricity –

Class of Equipment

CLASS I CLASS II

CLASS III

Class 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 Equipment

CLASS I EQUIPMENT

Class 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 Equipment

Electricity –

Class of Equipment

Class II equipment

The symbol for class II equipment is 2

concentric squares indicating double

insulation as shown below.

CLASS II EQUIPMENT

Class 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 –

Class of Equipment

Types of Equipment

The degree of protection for medical

electrical equipment is defined by the type

designation.

Electricity –

Types of Equipment

Type B Type BF Type CF

Type 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 parts

CF 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.

Electricity –

Types of Equipment

Normal 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 Tests

Single 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.


Single Fault Condition


Protective Earth Continuity

Applicable to Class1, all types

Limit 0.2 ohms

Insulation Tests

Applicable to Class 1, all types

Limit Not less than 50Mohms

Insulation Tests

Applicable to Class II, all types having applied parts

Limit : > 50 MOhms

Earth Leakage Current

Applicable to: Class 1 equipment all types

Limits: 0.5mA in NC, 1mA in SFC or 5mA and 10mA respectively for permanently installed equipment

Enclosure Leakage Current

Applicable to Class 1 and class II equipment , all types.

Limit0.1mA in NC, 0.5mA in SFC


Applicable to All Classes B and BF equipment having applied parts

Limits 0.1mA in NC, 0.5mA in SFC


Applicable to All equipment having applied parts.

Limits 0.1mA in NC, 0.5mA in SFC

Mains on Applied Parts

Applicable to Class 1 and class II equipment , types BF&CF equipment having applied parts.

Limits BF 5mA; CF 0.05mA per electrode

Safety Test as done by

BEMS

Electrical 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 Review

Report, tag, and do not use equipment with:

• Frayed wires or cracked insulation

• Damaged plugs or missing ground prongs


Report, tag, and do not use receptacles with:

• Only two slots

• Missing cover plates

• Loose mountings

• Weak gripping force


Inspections of Equipment: -

• Check of Strain-Relief

Electrical Safety

Review

Avoid:

• 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


Be 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


Always use your common sense

Do not end up like this person!


ELECTRICAL SAFETY

THE END

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medical electrical safety

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