Electrical Safety of Medical Equipment

7/29/2019 Electrical Safety of Medical Equipment

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Electrical Safety of Medical Equipment

Hazards Physiological Effects Leakage Currents Classes & Types Standards & Guidance Electrical Safety Test & Inspection General Points on Safety Bibliography

1 Hazards of Medical Electrical EquipmentMedical electrical equipment can present a range of hazards to the patient, the user, or

to service personnel. Many such hazards are common to many or all types of medicalelectrical equipment, whilst others are peculiar to particular categories of equipment.

The hazard presented by electricity exists in all cases where medical electrical

equipment is used, and there is therefore both a moral and legal obligation to takemeasures to minimise the risk. Because there is currently very little official guidance

on precisely what measures should be in place in order to achieve this in respect tomedical equipment, user organisations have developed procedures based on their ownexperience and risk assessments. The information in these notes is intended to assistin the development of suitable procedures to this end.

Any test and inspection regime intended to minimise the electrical risks from medical

electrical equipment should take into account the likely degree of risk from electricalhazards compared to other hazards of medical equipment. For this reason, varioushazards associated with medical electrical equipment are discussed briefly below.

1.1 Mechanical Hazards

All types of medical electrical equipment can present mechanical hazards. These can

range from insecure fittings of controls to loose fixings of wheels on equipment

trolleys. The former may prevent a piece of life supporting equipment from being

operated properly, whilst the latter could cause serious accidents in the clinical

environment.

Such hazards may seem too obvious to warrant mentioning, but it is unfortunately all

too common for such mundane problems to be overlooked whilst problems of a moretechnical nature are addressed.

1.2 Risk of fire or explosion
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All mains powered electrical equipment can present the risk of fire in the event of

certain faults occurring such as internal or external short circuits. In certainenvironments such fires may cause explosions. Although the use of flammableanaesthetics is not common today, it should be recognised that many of the medical

gases currently in use, such oxygen or nitrous oxide, vigorously support combustion.Wherever there is an elevated concentration of such gases, there is an increased risk

of fire initiated by electrical faults.

1.3 Absence of Function

Since many pieces of medical electrical equipment are life supporting or monitor vital

functions, the absence of function of such a piece of equipment would not be merely

inconvenient, but could threaten life.

1.4 Excessive or insufficient outputIn order to perform its desired function equipment must deliver its specified output.

Too high an output, for example, in the case of surgical diathermy units, would clearly

be hazardous. Equally, too low an output would result in inadequate therapy, which inturn may delay patient recovery, cause patient injury or even death. This highlights

the importance of correct calibration procedures.

1.5 InfectionMedical equipment that has been inadequately decontaminated after use may cause

infection through the transmission of microorganisms to any person who subsequentlycomes into contact with it. Clearly, patients, nursing staff and service personnel arepotentially at risk here.

1.6 Misuse

Misuse of equipment is one of the most common causes of adverse incidents involvingmedical devices. Such misuse may be a result of inadequate user training or of poor

user instructions.

1.7 Risk of exposure to spurious electric currents

All electrical equipment has the potential to expose people to the risk of spurious

electric currents. In the case of medical electrical equipment, the risk is potentiallygreater since patients are intentionally connected to such equipment and may not

benefit from the same natural protection factors that apply to people in othercircumstances. Whilst all of the hazards listed are important, the prevention of many ofthem require methods peculiar to the particular type of equipment under

consideration. For example, in order to avoid the risk of excessive output of surgicaldiathermy units, knowledge of radio frequency power measurement techniques isrequired. However, the electrical hazards are common to all types of medical electrical


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equipment and can minimised by the use of safety testing and inspection regimes

which can be applied to all types of medical electrical equipment.

2.1 Electrolysis

The movement of ions of opposite polarities in opposite directions through a medium iscalled electrolysis and can be made to occur by passing DC current through body

tissues or fluids. If a DC current is passed through body tissues for a period of

minutes, ulceration begins to occur. Such ulcers, while not normally fatal, can bepainful and take long periods to heal.

2.2 BurnsWhen an electric current passes through any substance having electrical resistance,

heat is produced. The amount of heat depends on the power dissipated (I2R). Whetheror not the heat produces a burn depends on the current density.

Human tissue is capable of carrying electric current quite successfully. Skin normally

has a fairly high electrical resistance while the moist tissue underneath the skin has amuch lower resistance. Electrical burns often produce their most marked effects near

to the skin, although it is fairly common for internal electrical burns to be produced,which, if not fatal, can cause long lasting and painful injury.

2.3 Muscle cramps

When an electrical stimulus is applied to a motor nerve or a 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 an external

electrical stimulus is responsible for the phenomenon where a person who is holding anelectrically live object can be unable to let go.

2.4 Respiratory arrest

The muscles between the ribs (intercostal muscles) need to repeatedly contract andrelax in order to facilitate breathing. Prolonged tetanus of these muscles can therefore

prevent breathing.

2.5 Cardiac arrestThe heart is a muscular organ, which needs to be able to contract and relaxrepetitively in order to perform its function as a pump for the blood. Tetanus of the

heart musculature will prevent the pumping process.

2.6 Ventricular fibrillation


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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 ventriclesundergoes irregular, uncoordinated twitching resulting in no net blood flow. Thecondition proves fatal if not corrected in a very short space of time.

Ventricular fibrillation can be triggered by very small electrical stimuli. A current as low

as 70 mA flowing from hand to hand across the chest, or 20A directly through theheart may be sufficient. It is for this reason that most deaths from electric shock areattributable to the occurrence of ventricular fibrillation.

2.7 Effect of frequency on neuro-muscular stimulation

The amount of current required to stimulate muscles is dependent to some extent onfrequency. Referring to figure 1, it can be seen that the smallest current required to

prevent the release of an electrically live object occurs at a frequency of around 50 Hz.

Above 10 kHz the neuro-muscular response to current decreases almost exponentially.

Figure 1. Current required to prevent release of a live object.

2.8 Natural protection factors

Many people have received electric shocks from mains potentials and above and lived

to tell the tale. Part of the reason for this is the existence of certain natural protectionfactors.

Ordinarily, a person subject to an unexpected electrical stimulus is protected to some

extent by automatic and intentional reflex actions. The automatic contraction ofmuscles on receiving an electrical stimulus often acts to disconnect the person from

the source of the stimulus. Intentional reactions of the person receiving the shocknormally serve the same purpose. It is important to realise that a patient in the clinicalenvironment who may have electrical equipment intentionally connected to them andmay also be anaesthetised is relatively unprotected by these mechanisms.

Normally, a person who is subject to an electric shock receives the shock through the

skin, which has a high electrical resistance compared to the moist body tissues below,


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and hence serves to reduce the amount of current that would otherwise flow. Again, a

patient does not necessarily enjoy the same degree of protection. The resistance of theskin may intentionally have been lowered in order to allow good connections ofmonitoring electrodes to be made or, in the case of a patient undergoing surgery,

there may be no skin present in the current path.

The absence of natural protection factors as described above highlights the need forstringent electrical safety specifications for medical electrical equipment and for routinetest and inspection regimes aimed at verifying electrical safety.

Leakage currents

Most safety testing regimes for medical electrical equipment involve the measurementof certain "leakage currents", because the level of them can help to verify whether or

not a piece of equipment is electrically safe. In this section the various leakage

currents that are commonly measurable with medical equipment safety testers aredescribed and their significance discussed. The precise methods of measurement alongwith applicable safe limits are discussed later under paragraphs at 6.

3.1 Causes of leakage currentsIf any conductor is raised to a potential above that of earth, some current is bound to

flow from that conductor to earth. This is true even of conductors that are wellinsulated from earth, since there is no such thing as perfect insulation or infinite

impedance. The amount of current that flows depends on:

a. the voltage on the conductor.b. the capacitive reactance between the conductor and earth.c. the resistance between the conductor and earth.

The currents that flow from or between conductors that are insulated from earth and

from each other are called leakage currents, and are normally small. However, sincethe amount of current required to produce adverse physiological effects is also small,such currents must be limited by the design of equipment to safe values.

For medical electrical equipment, several different leakage currents are defined

according to the paths that the currents take.

3.2 Earth leakage current

Earth leakage current is the current that normally flows in the earth conductor of a

protectively earthed piece of equipment. In medical electrical equipment, very often,the mains is connected to a transformer having an earthed screen. Most of the earthleakage current finds its way to earth via the impedance of the insulation between the


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transformer primary and the inter-winding screen, since this is the point at which the

insulation impedance is at its lowest (see figure 2).

Figure 2. Earth leakage current path

Under normal conditions, a person who is in contact with the earthed metal enclosureof the equipment and with another earthed object would suffer no adverse effects evenif a fairly large earth leakage current were to flow. This is because the impedance to

earth from the enclosure is much lower through the protective earth conductor than itis through the person. However, if the protective earth conductor becomes open

circuited, then the situation changes. Now, if the impedance between the transformerprimary and the enclosure is of the same order of magnitude as the impedancebetween the enclosure and earth through the person, a shock hazard exists.

It is a fundamental safety requirement that in the event of a single fault occurring,

such as the earth becoming open circuit, no hazard should exist. It is clear that inorder for this to be the case in the above example, the impedance between the mains

part (the transformer primary and so on) and the enclosure needs to be high. Thiswould be evidenced when the equipment is in the normal condition by a low earth

leakage current. In other words, if the earth leakage current is low then the risk ofelectric shock in the event of a fault is minimised.

3.3 Enclosure leakage current or touch current

The terms "enclosure leakage current" and "touch current" should be taken to be

synonymous. The former term is used in the bulk of this text. The terms are furtherdiscussed in connection with the electrical test methodsunder paragraphs 6.6 (Part 6).

Enclosure leakage current is defined as the current that flows from an exposed

conductive part of the enclosure to earth through a conductor other than the protective

earth conductor.

If a protective earth conductor is connected to the enclosure, there is little point in

attempting to measure the enclosure leakage current from another protectively

earthed point on the enclosure, since any measuring device used is effectively shorted

out by the low resistance of the protective earth. Equally, there is little point inmeasuring the enclosure leakage current from a protectively earthed point on theenclosure with the protective earth open circuit, since this would give the same reading

as measurement of earth leakage current as described above. For these reasons, it is
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usual when testing medical electrical equipment to measure enclosure leakage current

from points on the enclosure that are not intended to be protectively earthed (seefigure 3). On many pieces of equipment, no such points exist. This is not a problem.The test is included in test regimes to cover the eventuality where such points do exist

and to ensure that no hazardous leakage currents will flow from them.

Figure 3. Enclosure leakage current path

3.4 Patient leakage current

Patient leakage current is the leakage current that flows through a patient connected

to an applied part or parts. It can either flow from the applied parts via the patient to

earth or from an external source of high potential via the patient and the applied partsto earth. Figures 4a and 4b illustrate the two scenarios.

Figure 4a. Patient leakage current path from equipment


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Figure 4b. Patient leakage current path to equipment

3.5 Patient auxiliary current

The patient auxiliary current is defined as the current that normally flows betweenparts of the applied part through the patient, which is not intended to produce aphysiological effect (see figure 5).

Figure 5. Patient auxiliary current path

Classes and types of medical electrical equipment

Hazards

Physiological Effects Leakage Currents Classes & Types Standards & Guidance Electrical Safety Test & Inspection General Points on Safety Bibliography


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All electrical equipment is categorised into classes according to the method of

protection against electric shock that is used. For mains powered electrical equipmentthere are usually two levels of protection used, called "basic" and "supplementary"protection. The supplementary protection is intended to come into play in the event of

failure of the basic protection.

4.1 Class I equipment

Class I equipment has a protective earth. The basic means of protection is the

insulation between live parts and exposed conductive parts such as the metalenclosure. In the event of a fault that would otherwise cause an exposed conductive

part to become live, the supplementary protection (i.e. the protective earth) comes

into effect. A large fault current flows from the mains part to earth via the protectiveearth conductor, which causes a protective device (usually a fuse) in the mains circuit

to disconnect the equipment from the supply.

It is important to realise that not all equipment having an earth connection is

necessarily class I. The earth conductor may be for functional purposes only such as

screening. In this case the size of the conductor may not be large enough to safelycarry a fault current that would flow in the event of a mains short to earth for thelength of time required for the fuse to disconnect the supply.

Class I medical electrical equipment should have fuses at the equipment end of the

mains supply lead in both the live and neutral conductors, so that the supplementary

protection is operative when the equipment is connected to an incorrectly wired socketoutlet.

Further confusion can arise due to the use of plastic laminates for finishing equipment.A case that appears to be plastic does not necessarily indicate that the equipment isnot class I.

There is no agreed symbol in use to indicate that equipment is class I and it is not

mandatory to state on the equipment itself that it is class I. Where any doubt exists,reference should be made to equipment manuals.

The symbols below may be seen on medical electrical equipment adjacent to terminals.

Figure 6. Symbols seen on earthed equipment.

4.2 Class II equipment

The method of protection against electric shock in the case of class II equipment iseither double insulation or reinforced insulation. In double insulated equipment the

basic protection is afforded by the first layer of insulation. If the basic protection fails


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then supplementary protection is provided by a second layer of insulation preventing

contact with live parts.

In practice, the basic insulation may be afforded by physical separation of live

conductors from the equipment enclosure, so that the basic insulation material is air.The enclosure material then forms the supplementary insulation.

Reinforced insulation is defined in standards as being a single layer of insulationoffering the same degree of protection against electric shock as double insulation.

Class II medical electrical equipment should be fused at the equipment end of the

supply lead in either mains conductor or in both conductors if the equipment has afunctional earth.

The symbol for class II equipment is two concentric squares illustrating doubleinsulation as shown below.

Figure 7. Symbol for class II equipment

4.3 Class III equipmentClass III equipment is defined in some equipment standards as that in which protection

against electric shock relies on the fact that no voltages higher than safety extra lowvoltage (SELV) are present. SELV is defined in turn in the relevant standard as a

voltage not exceeding 25V ac or 60V dc.

In practice such equipment is either battery operated or supplied by a SELVtransformer.

If battery operated equipment is capable of being operated when connected to the

mains (for example, for battery charging) then it must be safety tested as either classI or class II equipment. Similarly, equipment powered from a SELV transformer shouldbe tested in conjunction with the transformer as class I or class II equipment as

appropriate.

It is interesting to note that the current IEC standards relating to safety of medicalelectrical equipment do not recognise Class III equipment since limitation of voltage isnot deemed sufficient to ensure safety of the patient. All medical electrical equipment

that is capable of mains connection must be classified as class I or class II. Medical

electrical equipment having no mains connection is simply referred to as "internallypowered".


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4.4 Equipment types

As described above, the class of equipment defines the method of protection againstelectric shock. The degree of protection for medical electrical equipment is defined bythe type designation. The reason for the existence of type designations is that different

pieces of medical electrical equipment have different areas of application and thereforedifferent electrical safety requirements. For example, it would not be necessary to

make a particular piece medical electrical equipment safe enough for direct cardiacconnection if there is no possibility of this situation arising.

Table 1 shows the symbols and definitions for each type classification of medical

electrical equipment.

Type Symbol Definition

B

Equipment providing a particular degree of

protection against electric shock, particularlyregarding allowable leakage currents and reliability

of the protective earth connection (if present).

BFAs type B but with isolated or floating (F - type)applied part or parts.

CF

Equipment providing a higher degree of protectionagainst electric shock than type BF, particularly

with regard to allowable leakage currents, andhaving floating applied parts.

Table 1. Medical electrical equipment types

All medical electrical equipment should be marked by the manufacturer with one of thetype symbols above.

5.1 Type tests and routine testsBefore discussing the documentation relevant to electrical safety of medical electrical

equipment, it is important to distinguish between "type tests" and routine tests.

Standards for the manufacture of equipment normally detail tests which are intended

to be carried out on a single representative sample of a piece of equipment for which


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certification of compliance with a standard is being sought. Such tests are carried out

by approved test houses under tightly specified environmental conditions. These testsare called "type tests" and are not intended for routine use. Indeed, repetition of manyof the tests would certainly cause deterioration in performance and safety of the

equipment under test.

Routine tests have an entirely different purpose than that for type tests. Routine testsare intended to provide good indicators to the safety of equipment without subjectingit to undue stress that would be liable to cause deterioration.

In summary then, it should be understood that International ElectrotechnicalCommission (IEC) or British Standards (BS) manufacturers' standards for medical

electrical equipment referred to below are intended only for type testing and should

not be used for acceptance, in-service or routine testing of equipment. However, anytests that are used for the latter purposes should ideally be consistent with thestandards to which the equipment has been manufactured. Routine tests and test

limits may therefore be derived (in modified form) from the standards, with the strictproviso that any such tests should not damage or even stress the equipment undertest.

5.2 HTM 8

In 1963, the Department of Health and Social Security published Hospital Technical

Memorandum number 8 called "safety code for electro-medical apparatus". The

purpose of the document was to establish adequate standards for the design andconstruction of electro-medical apparatus since no other relevant national standard

existed at the time. Although the document was produced essentially for the guidanceof manufacturers, biomedical departments in hospitals were quick to adopt tests from

the document for the basis of their own medical electrical equipment safety testing

regimes. Although tests detailed in the code were type tests, many of them could be

fairly easily be repeated without adverse effects on the equipment as routine tests.Performance of the electrical safety tests was made easier by the development ofspecialised medical equipment safety testers, specifically, the Liverpool tester. The

HTM was withdrawn on publication of BS5724 part 1 (see below).

5.3 BS 5724 or IEC 60601

In 1979, HTM 8 was superseded by the British Standard BS 5724 part 1. Thisdocument is a comprehensive specification for safety of medical electrical equipment.

Part 1 covers the general requirements, i.e. requirements common to all medical

electrical equipment regardless of function. A series of part 2's detailing particularrequirements for specific categories of medical electrical equipment followed

publication of part 1 (see Annex 1).

BS 5724 is a far more detailed document than HTM 8, which it replaced. Like the HTM,

the tests contained in the standard are type tests. Some guidance was given in the

1979 edition of the standard on recommended testing during manufacture and/orinstallation. Unfortunately, some routine test regimes based on BS 5724 tended to betoo rigorous for such application and in some cases caused damage to equipment.


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BS 5724 part 1 was revised in 1989, making it identical to the International Electro-

technical Commission standard IEC 601-1: 1988. References to routine tests weremade even less specific than in the previous edition. The standard was subsequentlyre-numbered as IEC 60601-1.

Any manufacturer obtaining compliance of an item of their equipment to BS5724 or

IEC 60601 will be in possession of a uniquely numbered certificate issued by the testhouse verifying that fact. Compliance to the standard is a commonly used route usedby manufacturers to obtain CE marking (see paragraphs at 5.6.1 below).

5.3.1 The Third Edition of IEC60601-1

The third edition of IEC60601-1 was introduced in December 2005. The standard hasbeen renamed "General requirements for basic safety and essential performance" to

reflect the fact that inadequate equipment performance may give rise to hazards. The

new standard is stated to replace the second edition, although it is recognised that, inpractice, due to the references made to the general standard by particular standards

(part twos), there is likely to be a fairly long transitionary period for compliance by

equipment manufacturers.

There are some significant changes in the new standard, some of which are worthnoting here.

The new standard states that the manufacturer must have in place a risk managementprocess that complies to the requirements of ISO 14971 in order to ensure that theequipment design process results in equipment that is suitable for its intended purpose

and that any risks associated with its use are acceptable.

Certain changes in terminology and numbering systems have been introduced in orderto make the standard more compatible with other IEC standards, in particular IEC

60950-1 (Information technology equipment).

Collateral standards for medical electrical systems (IEC 60601-1-1) and programmableelectrical medical systems (IEC 60601-1-4) have been incorporated into the body of

the new standard as new clauses.

5.4 Guidance from the UK Department of Health

The Department of Health has, in the past, issued two stand alone documents giving

detailed guidance on acceptance testing or pre-use checks on medical devices.Although both of these documents have been superseded, they are discussed briefly

below because they have been used by many equipment user organisations as the

basis for acceptance testing regimes, and even for routine testing regimes.Additionally, a number of manufacturers of medical equipment safety testers have

incorporated protocols derived from these guidance documents into their testers'firmware.

A comparison between the test recommendations of both documents is provided inannex 2 for information.


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5.4.1 Hospital Equipment Information 95

In August 1981, the DHSS issued HEI 95 entitled "Code of practice for acceptancetesting of medical electrical equipment". The document was produced partly to addressthe problems that had arisen due to the misapplication of type tests from BS 5724 by

some NHS biomedical departments.

As indicated by the title of the document, the code of practice detailed inspection andtest procedures to be performed on newly acquired medical electrical equipment beforeit was put into service. Inspection procedures were clearly explained and the standardacceptance test log sheet given in the appendix of the document contained references

to the explanatory text.

The electrical safety testing recommendations offered in HEI 95 provided a testing

regime that was effective whilst being considerably simpler than many test regimesthat were developed from the recommendations of BS 5724. The reason for this is thatthe recommended electrical safety tests are generally applied under worst-case

conditions.

Although designed as a code of practice for acceptance testing the document has beenwidely adopted and used as the basis of routine test regimes by hospital biomedicaldepartments.

The document was officially withdrawn in December 1999 on the publication by theMedical Devices Agency of MDA DB9801 Supplement 1 (see below).

5.4.2 DB9801 Supplement 1In December 1999, the Medical Devices Agency (now the Medicines and Healthcare

Products Regulatory Agency or MHRA) published Device Bulletin 9801 Supplement 1entitled "Checks and tests for newly delivered medical devices". The document was a

supplement to Device Bulletin 9801, "Medical device and equipment management forhospital and community based organisations", which was published by the Medical

Devices Agency in January 1998. The supplement superseded HEI 95.

The document was intended to be applicable to all newly delivered medical devices,

including non-electrical equipment, before being placed into service. Delivery checksdetailed included paperwork checks, visual inspection procedures and functionalchecks. Electrical safety checks and tests as well as calibration checks were also

recommended.

DB9801 Supplement 1 emphasised that new equipment under test should not be

subjected to currents or voltages exceeding those experienced under normal operating

conditions. Hence none of the recommended tests involved shorting applied partstogether or applying high voltages to electrodes. It was also suggested that medical

electrical equipment not having applied parts could be safety tested satisfactorily usingnon-specialist portable appliance testers.

Specimen forms for recording the results of checks and tests were given in thedocument. Rationales for the checks and tests prescribed were also given in the

annexes of the document.


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DB0801 and its supplements were replaced by DB2006(05) in November 2006 (see

below).

5.4.3 Device Bulletin DB2006(05)

In November 2006, the MHRA published (on their website only) Device BulletinDB2006(05) - "Managing Medical Devices - Guidance for healthcare and social servicesorganisations". The document updates and replaces guidance previously given in

DB9801 ("Medical device and Equipment Management for hospital and community

based organisations") and its supplements. Section 4 of the new guidance addresses"Delivery of a new piece of equipment" and hence replaces guidance previously given

in DB9801 Supplement 1. Having said that, much of the basic philosophy behind, and

recommendations from, the latter document have been retained.

The guidance stresses the importance of acceptance checks as a means of improving

efficiency and reducing risk. It also emphasises the necessity of recording checks andtest results in order to meet health and safety requirements, possible litigationdemands and to enable safe and effective future device management.

Delivery checks relevant to medical electrical equipment on delivery are divided into

administrative tasks ("paperwork/database") and visual inspection. Recommendedadministrative checks and tasks include:-

device compatibility with purchase specification inclusion and appropriateness of user and service instructions inclusion of compliance and calibration certificates and test results adding device details to equipment management records check for special requirements such as need for decontamination before use

The guidance further recommends that functional checks, electrical safety tests and

calibration checks (where appropriate) should be carried out prior to the equipmentbeing placed into service.

No specific detail is given on safety tests, other than to emphasise that "pre-use tests

should not exceed the bounds of normal use". In connection with this, it states that thetests described in IEC 60601-1 are "type tests" and are therefore not suitable for pre-use or maintenance tests (see paragraphs at 5.1 above).

The guidance does, however, point out the legal requirements for electrical safetytesting under the Health and Safety at Work etc Act 1974 and the Electricity at Work

Regulations 1989. The guidance states that "Responsible organisations should ensure

that they have implemented electrical safety testing procedures to comply with this

legislation". The legal requirements are further discussed in these notes underparagraphs at 5.6 below.

The full text of DB2006(05) is available free of charge on the MHRA website at

www.mhra.gov.uk

5.5 Future Guidance


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The International Electrotechnical Commission has been preparing IEC 62353 Edition

1: "Medical Electrical Equipment - Recurrent test and test after repair of medicalequipment" for some years. Publication of this document is expected in the nearfuture.

Also in preparation by the Institute of Physics and Engineering in Medicine (IPEM) is a

publication called "Electrical Safety Testing: A Workbench Guide".

5.6 UK Legislation

There are a number of items of legislation applicable in the UK that impact in a fairly

direct way on maintenance procedures for medical electrical devices. These arediscussed briefly below.

5.6.1 Medical Devices Directive

Since the Medical Devices Directive (Council Directive 93/42/EEC) became law in the

UK in 1994, it has been mandatory that all medical devices put on to the market areappropriately CE marked to indicate compliance with the directive. An important

component of the directive is a list of "essential requirements" to which all medical

devices must comply. Compliance with these requirements can be interpretedessentially as meaning that the medical device is fit for purpose.

Depending on the risk class under which a particular medical device is classified, there

are various means by which a manufacturer is able to demonstrate conformity with the

directive. For devices in the lowest risk category (class I), self declaration isacceptable, whilst for medium and higher risk devices (classes IIa, IIb and III), the

assessment route is more rigorous and may include auditing of the manufacturers'

quality assurance system and independent type testing to a recognised standard (e.g.IEC 60601) of a representative production sample by a "notified body". Each notified

body may be identified by a unique number that appears to the top right of the CEmark on medical devices.

In each member state a "Competent Authority" is authorised by that country's

government to ensure that the requirements of the directive are carried out. In the UK,the competent authority is the Secretary of State for Health who has delegated day to

day running of the competent authority to the Medicines and Healthcare ProductsRegulatory Agency (MHRA). The Medical Devices Directive is enshrined into UK law bythe medical Devices Regulations 2002.

As far as the purchaser of equipment is concerned, all medical devices purchased

within any EEC member state should be appropriately CE marked. Conformity to the

directive should be confirmed by the equipment supplier by means of a "declaration ofconformity" prior to purchase.

5.6.2 Health and Safety at Work etc. Act 1974The Health and Safety at Work etc. Act 1974 (HASAWA) act may be regarded as the

"catch all" act that covers all aspects of health and safety in the workplace. It places

responsibility on employers and employees for the health, safety and welfare of allpersons that may be affected by activities of an employer (including NHS Trusts). The


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overarching nature of the act is illustrated by part 1, section 3, paragraph 1 of the act

that states:

"It shall be the duty of every employer to conduct his undertaking in such a way as to

ensure, so far as is reasonably practicable, that persons not in his employment whomay be affected thereby are not thereby exposed to risks to their health and safety".

There are many sets of Regulations that are made under the act that spell out in detailwhat must be done to meet the requirements of the act. The Regulations are said to be

"made under the Act", and non-conformity to any such regulations is therefore an

offence under the HASAWA.

5.6.3 Electricity at Work Regulations 1989

Particular requirements with regard to electrical equipment are imposed by theElectricity at Work Regulations 1989. Some significant extracts from the regulations

are quoted below. It should be noted when reading them that the word "systems"

refers to electrical installations and any equipment capable of being made live by

them.

Regulation 4(1)"All systems shall at all times be of such construction as to prevent,so far as is reasonably practicable, danger".

Regulation 4(2)"As necessary to prevent danger, all systems shall be maintained soas to prevent, so far as is reasonably practicable, such danger".

Regulation 4(3)"Every work activity, including operation, use and maintenance of a

system and work near a system, shall be carried out in such a manner as not to giverise, so far as is reasonably practicable, to danger".

Regulation 16"No person shall be engaged in any work activity where knowledge orexperience is necessary to prevent danger or, where appropriate, injury, unless hepossesses such knowledge or experience, or is under such degree of supervision as

may be appropriate having regard to the nature of the work."

Although the Electricity at Work Regulations clearly put requirements on employers

and employees with regard to the necessity for maintaining electrical safety, themeans by which this should be done are not spelt out in the Regulations.

5.6.4 Management of Health and Safety at Work Regulations 1999

The Management of Health and Safety at Work Regulations 1999 set out the need for

organisations to develop formalised management systems for health and safety. These

systems will form a part of the organisations health and safety policy.

The policy should detail arrangements for effective planning, organisation, control,

monitoring and review of protective and preventative measures. Hence protocols forelectrical safety inspection and testing of medical equipment should be a part of thispolicy.


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A major plank of the regulations is prescription of the use of risk assessments as a tool

in managing health and safety effectively. The prime obligation under health andsafety legislation is to eliminate or minimise risks to health and safety of anyone whomay be affected by work activities. Safe systems of work and effective preventative

measures to achieve this can only be developed following effective risk assessments.

Electrical Safety Tests


The following paragraphs and diagrams describe the electrical safety tests commonlyavailable on medical equipment safety testers. Please note that although HEI 95 and

DB9801 are no longer current, they are referred to in the text since many medical

electronics departments have used them as a basis for local acceptance testing andeven routine testing protocols. Protocols based on both sets of guidance are alsoavailable on many medical equipment safety testers.

6.1 Normal condition and single fault conditions

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 ofprotection against a hazard, no safety hazard should arise. Such conditions are called

"single fault conditions" (SFCs) and include such situations as the interruption of theprotective earth conductor or of one supply conductor, the appearance of an external

voltage on an applied part, the failure of basic insulation or of temperature limitingdevices.

Where a single fault condition is not applied, the equipment is said to be in "normal

condition" (NC). However, it is important to understand that even in this condition, the

performance of certain tests may compromise the means of protection against electric

shock. For example, if earth leakage current is measured in normal condition, theimpedance of the measuring device in series with the protective earth conductormeans that there is no effective supplementary protection against electric shock.

Many electrical safety tests are carried out under various single fault conditions inorder to verify that there is no hazard even should these conditions occur in practice. Itis often the case that single fault conditions represent the worst case and will give themost adverse results. Clearly the safety of the equipment under test may be

compromised when such tests are performed. Personnel carrying out electrical safety

tests should be aware that the normal means for protection against electric shock arenot necessarily operative during testing and should therefore exercise due precautionsfor their own safety and that of others. In particular the equipment under test should

not be touched during the safety testing procedure by any persons.


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6.2 Protective Earth Continuity

The resistance of the protective earth conductor is measured between the earth pin onthe mains plug and a protectively earthed point on the equipment enclosure (see figure6). The reading should not normally exceed 0.2 at any such point. The test is

obviously only applicable to class I equipment.

In IEC60601, the test is conducted using a 50Hz current between 10A and 25A for aperiod of at least 5 seconds. Although this is a type test, some medical equipmentsafety testers mimic this method. Damage to equipment can occur if high currents arepassed to points that are not protectively earthed, for example, functional earths.

Great care should be taken when high current testers are used to ensure that theprobe is connected to a point that is intended to be protectively earthed.

HEI 95 and DB9801 Supplement 1 recommended that the test be carried out at acurrent of 1A or less for the reason described above.

Where the instrument used does not do so automatically, the resistance of the testleads used should be deducted from the reading.

If protective earth continuity is satisfactory then insulation tests can be performed.

Applicable to Class I, all types

Limit: 0.2

DB9801 recommended?: Yes, at 1A or less.

HEI 95 recommended?: Yes, at 1A or less.

Notes: Ensure probe is on a protectively earthed point

Figure 8. Measurement of protective earth continuity.

6.3 Insulation Tests

IEC 60601-1 (second edition), clause 17, lays down specifications for electrical

separation of parts of medical electrical equipment compliance to which is essentially


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verified by inspection and measurement of leakage currents. Further tests on

insulation are detailed under clause 20, "dielectric strength". These tests use ACsources to test equipment that has been pre-conditioned to specified levels ofhumidity. The tests described in the standard are type tests and are not suitable for

use as routine tests.

HEI 95 and DB9801 recommended that for class I equipment the insulation resistancebe measured at the mains plug between the live and neutral pins connected togetherand the earth pin. Whereas HEI 95 recommended using a 500V DC insulation tester,DB 9801 recommended the use of 350V DC as the test voltage. In practice this last

requirement could prove difficult and it was acknowledged in a footnote that a 500 VDC test voltage is unlikely to cause any harm. The value obtained should normally bein excess of 50M but may be less in exceptional circumstances. For example,equipment containing mineral insulated heaters may have an insulation resistance as

low as 1M with no fault present. The test should be conducted with all fuses intactand equipment switched on where mechanical on/off switches are present (see figure9).

Applicable to Class I, all types

Limits: Not less than 50M

DB9801recommended?:

Yes

HEI 95recommended?:

Yes

Notes:Equipment containing mineral insulated heaters may give valuesdown to 1M. Check equipment is switched on.

Figure 9. Measurement of insulation resistance for class I equipment

HEI 95 further recommended for class II equipment that the insulation resistance bemeasured between all applied parts connected together and any accessible conductive

parts of the equipment. The value should not normally be less than 50M (see figure10). DB9801 Supplement 1 did not recommend any form of insulation test be appliedto class II equipment.


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Applicable to Class II, all types having applied parts

Limits: not less than 50M.

DB9801 recommended?: No

HEI 95 recommended?: YesNotes: Move probe to find worst case.

Figure 10. Measurement of insulation resistance for class II equipment.

Satisfactory earth continuity and insulation test results indicate that it is safe toproceed to leakage current tests.

6.4 Leakage current measuring device

The leakage current measuring device recommended by IEC 60601-1 loads the

leakage current source with a resistive impedance of about 1 k and has a half powerpoint at about 1kHz. The recommended measuring device was changed slightly in

detail between the 1979 and 1989 editions of the standard but remained functionallyvery similar. Figure 11 shows the arrangements for the measuring device. The millivolt

meter used should be true RMS reading and should have an input impedance greater

than 1 M. In practice this is easily achievable with most good quality modernmultimeters. The meter in the arrangements shown measures 1mV for each A of

leakage current.

Figure 11. Arrangements for measurement of leakage currents.


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6.5 Earth Leakage Current

For class I equipment, earth leakage current is measured as shown in figure 12. Thecurrent should be measured with the mains polarity normal and reversed. HEI 95 andDB9801 Supplement 1 recommended that the earth leakage current be measured in

normal condition (NC) only. Many safety testers offer the opportunity to perform thetest under single fault condition, neutral conductor open circuit. This arrangement

normally gives a higher leakage current reading.

One of the most significant changes with regard to electrical safety in the 2005 edition

of IEC 60601-1 is an increase by a factor of 10 in the allowable earth leakage current

to 5mA in normal condition and 10mA under single fault condition. The rationale forthis is that the earth leakage current is not, of itself, hazardous.

Higher values of earth leakage currents, in line with local regulation and IEC 60364-7-710 (electrical supplies for medical locations), are allowed for permanently installedequipment connected to a dedicated supply circuit.

Applicable to Class I equipment, all types

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

equipment designed to IEC60601-1:2005.

DB9801recommended?: Yes, in normal condition only.

HEI 95recommended?:

Yes, in normal condition only.

Notes:Measure with mains normal and reversed. Ensure equipment isswitched on.

Figure 12. Measurement of earth leakage current.

6.6 Enclosure leakage current or touch current

Enclosure leakage current is measured between an exposed part of the equipment

which is not intended to be protectively earthed and true earth as shown in figure 13.

The test is applicable to both class I and class II equipment and should be performedwith mains polarity both normal and reversed. HEI 95 recommended that the test be

performed under the SFC protective earth open circuit for class I equipment and undernormal condition for class II equipment. DB9801 Supplement 1 recommended that the

test be carried out under normal condition only for both class I and class II equipment.


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Many safety testers also allow the SFC's of interruption of live or neutral conductors to

be selected. Points on class I equipment which are likely not to be protectively earthedmay include front panel fascias, handle assemblies etc.

The term "enclosure leakage current" has been replaced in the new edition of the IEC

60601-1standard by the term "touch current", bringing it into line with IEC 60950-1 for

information technology equipment. However, the limits for touch current are the sameas the limits for enclosure leakage current under the second edition of the standard, at0.1 mA in normal condition and 0.5 mA under single fault condition.

In practice, if a piece of equipment has accessible conductive parts that areprotectively earthed, then in order to meet the new requirements for touch current,

the earth leakage current would need to meet the old limits. This is due to the fact that

when the touch current is tested from a protectively earthed point with the equipmentprotective earth conductor disconnected, the value will be the same as that achievedfor earth leakage current under normal condition.

Hence, where higher earth leakage currents are recorded for equipment designed to

the new standard, it is important to check the touch current under single faultcondition, earth open circuit, from all accessible conductive parts.

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

Limits: 0.1mA in NC, 0.5mA in SFC

DB9801recommended?:

Yes, NC only

HEI 95recommended?:

Yes, class I SFC earth open circuit, class II NC.

Notes:Ensure equipment switched on. Normal and reverse mains. Move

probe to find worst case.

Figure 13. Measurement of enclosure leakage current

6.7 Patient leakage current

Under IEC 60601-1, for class I and class II type B and BF equipment, the patientleakage current is measured from all applied parts having the same function connected


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together and true earth (figure 14). For type CF equipment the current is measured

from each applied part in turn and the leakage current leakage must not be exceededat any one applied part (figure 15).

HEI 95 adhered to the same method, however, DB9801 Supplement 1 recommended

that patient leakage current be measured from each applied part in turn for all types of

equipment, although the recommended leakage current limits were not revised to takeinto account the changed test method for B and BF equipment.

Great care must be taken when performing patient leakage current measurements that

equipment outputs are inactive. In particular, outputs of diathermy equipment andstimulators can be fatal and can damage test equipment.

Applicable to All classes, type B & BF equipment having applied parts.

Limits: 0.1mA in NC, 0.5mA in SFC.

DB9801

recommended?:No

HEI 95 recommended?: Yes, class I SFC earth open circuit, class II normal condition.

Notes:Equipment on, but outputs inactive. Normal and reversemains.

Figure 14. Measurement of patient leakage current with applied parts connectedtogether


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Applicable toClass I and class II, type CF (B & BF for DB9801 only)equipment having applied parts.

Limits: 0.01mA in NC, 0.05mA in SFC.

DB9801recommended?:

Yes, all types, normal condition only.

HEI 95recommended?:

Yes, type CF only, class I SFC earth open circuit, class II normalcondition.

Notes:quipment on, but outputs inactive. Normal and reverse mains.

Limits are per electrode.

Figure 15. Measurement of patient leakage current for each applied part in turn

6.8 Patient auxiliary current

Patient auxiliary current is measured between any single patient connection and all

other patient connections of the same module or function connected together. Where

all possible combinations are tested together with all possible single fault conditionsthis yields an exceedingly large amount of data of questionable value.

Applicable to All classes and types of equipment having applied parts.

Limits:Type B & BF - 0.1mA in NC, 0.5mA in SFC.Type CF - 0.01mA in NC, 0.05mA in SFC.

DB9801 recommended?: No.

HEI 95 recommended?: No.

Notes: Ensure outputs are inactive. Normal and reverse mains.

Figure 16. Measurement of patient auxiliary current.

6.9 Mains on applied parts (patient leakage)

By applying mains voltage to the applied parts, the leakage current that would flowfrom an external source into the patient circuits can be measured. The measuring

arrangement is illustrated in figure 18.

Although the safety tester normally places a current limiting resistor in series with the

measuring device for the performance of this test, a shock hazard still exists.Therefore, great care should be taken if the test is carried out in order to avoid thehazard presented by applying mains voltage to the applied parts.


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Careful consideration should be given as to the necessity or usefulness of performing

this test on a routine basis when weighed against the associated hazard and thepossibility of causing problems with equipment. The purpose of the test under IEC60601-1 is to ensure that there is no danger of electric shock to a patient who for

some unspecified reason is raised to a potential above earth due to the connection ofthe applied parts of the equipment under test. The standard requires that the leakage

current limits specified are not exceeded. There is no guarantee that equipmentperformance will not be adversely affected by the performance of the test. In

particular, caution should be exercised in the case of sensitive physiologicalmeasurement equipment. In short, the test is a "type test".

Most medical equipment safety testers refer to this test as "mains on applied parts",although this is not universal. One manufacturer refers to the test simply as "Patientleakage - F-type". In all cases there should be a hazard indication visible where the

test is selected.

Applicable to Class I & class II, types BF & CF having applied parts.

Limit: Type BF - 5mA; type CF - 0.05mA per electrode.

DB9801 recommended?: No.

HEI 95 recommended?: No

Notes:

Ensure outputs are inactive. Normal and reverse mains.

Caution required, especially on physiological measurementequipment.

Figure 17. Mains on applied parts measurement arrangement

6.10 Leakage current summary

The following table summarises the leakage current limits (in mA) specified byIEC60601-1 (second edition) for the most commonly performed tests. Most equipment

currently in use in hospitals today is likely to have been designed to conform to this

standard, but note that the allowable values of earth leakage current have been

increased in the third edition of the standard as discussed above.

The values stated are for d.c. or a.c. (r.m.s), although later amendments of the

standard included separate limits for the d.c. element of patient leakage and patient

auxiliary currents at one tenth of the values listed below. These have not been

included in the table since, in practice, it is rare that there is a problem solely with d.c.leakage where that is not evidenced by a problem with combined a.c and d.c. leakage.


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Leakage currentType B

NC SFC

Type BF

NC SFC

Type CF

NC S

Earth 0.5 1 0.5 1 0.5 1

Earth for fixed equipment 5 10 5 10 5 10

Enclosure 0.1 0.5 0.1 0.5 0.1 0.5

Patient 0.1 0.5 0.1 0.5 0.01 0.0

Mains on applied part - - - 5 - 0.0

Patient auxiliary 0.1 0.5 0.1 0.5 0.01 0.0

* For class II type CF equipment HEI95 recommends a limit for enclosure leakage

current of 0.01mA as per the 1979 edition of BS 5724.

Table 2. Leakage current limits summary.

6.11 Comparison of HEI 95 and DB 9801 Supplement 1 recommendations

Test HEI 95 DB9801 Supplement 1

Earth continuityUse test current of 1A or lessLimit 0.2ohm

Use test current of 1A or lLimit 0.2ohm

Insulation for Class 1

equipment

Measure between L and Nconnected together and E using

500v DC tester.Limit > 50M. Investigate lowervalues

Measure between L and Nconnected together and E

350v DC tester.Limit > 20M. Investigatevalues

Insulation for Class IIequipment

Measure between applied partsand accessible conductive parts ofthe equipment.

Limit > 50M. Investigate lowervalues

No recommendation.

Earth leakage currentMeasure in normal condition

Limit < 0.5mA

Measure in normal conditi

Limit < 0.5mA

Enclosure leakage current

Measure in SFC, earth open circuitfor Class-1, NC for Class-IILimit


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Class II, B& BF < 0.1 mA Class I, CF < 0.05 mA per

electrode

Class II, CF < 0.01 mA perelectrode

electrode

Go to Part 7Test and Inspection Protocols

Test and Inspection Protocols

Hazards Physiological Effects Leakage Currents Classes & Types Standards & Guidance

Electrical Safety Test & Inspection General Points on Safety Bibliography

7.1 When to test

As discussed at paragraphs under 5.6 above, user organisations should design andimplement electrical safety inspection and test regimes on the basis of risk

assessments.

In practice, most user organisations have found it necessary to carry out electrical

inspection and safety testing on medical electrical equipment on the followingoccasions.

a. On newly acquired equipment prior to being accepted for useb. During routine planned preventative maintenance.c. After repairs have been carried out on equipment.

A patient should never be connected to a piece of equipment that has not beenchecked.

The testing regime used in the case of acceptance testing will be slightly different to

that used on other occasions particularly as regards checks on the condition of

packaging, presence of relevant documentation and accessories. However, it is usefulto use the acceptance testing procedure to lay down baseline data for comparisonwhen the equipment is tested on future scheduled services and after repairs.

7.2 Example inspection and test protocol

Annex 3 contains a test record sheet that is used to record inspection and test results

produced by a simple electrical safety protocol. It is not intended to be in any way
http://www.ebme.co.uk/arts/safety/part7.htmhttp://www.ebme.co.uk/arts/safety/part7.htmhttp://www.ebme.co.uk/arts/safety/index.htmhttp://www.ebme.co.uk/arts/safety/index.htmhttp://www.ebme.co.uk/arts/safety/part2.htmhttp://www.ebme.co.uk/arts/safety/part2.htmhttp://www.ebme.co.uk/arts/safety/part3.htmhttp://www.ebme.co.uk/arts/safety/part3.htmhttp://www.ebme.co.uk/arts/safety/part4.htmhttp://www.ebme.co.uk/arts/safety/part4.htmhttp://www.ebme.co.uk/arts/safety/part5.htmhttp://www.ebme.co.uk/arts/safety/part5.htmhttp://www.ebme.co.uk/arts/safety/part6.htmhttp://www.ebme.co.uk/arts/safety/part6.htmhttp://www.ebme.co.uk/arts/safety/part7.htmhttp://www.ebme.co.uk/arts/safety/part7.htmhttp://www.ebme.co.uk/arts/safety/part8.htmhttp://www.ebme.co.uk/arts/safety/part8.htmhttp://www.ebme.co.uk/arts/safety/part9.htmhttp://www.ebme.co.uk/arts/safety/part9.htmhttp://www.ebme.co.uk/arts/safety/part9.htmhttp://www.ebme.co.uk/arts/safety/part8.htmhttp://www.ebme.co.uk/arts/safety/part7.htmhttp://www.ebme.co.uk/arts/safety/part6.htmhttp://www.ebme.co.uk/arts/safety/part5.htmhttp://www.ebme.co.uk/arts/safety/part4.htmhttp://www.ebme.co.uk/arts/safety/part3.htmhttp://www.ebme.co.uk/arts/safety/part2.htmhttp://www.ebme.co.uk/arts/safety/index.htmhttp://www.ebme.co.uk/arts/safety/part7.htm


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prescriptive, but is included here simply to illustrate many of the important features of

an effective protocol.

Details of the equipment under test are recorded at the top of the form including the

device serial number and a plant number ascribed by the user organisation. Thisensures that the record can be linked to the particular item of equipment. The class

and type/s of the equipment under test are also recorded here to ensure thatappropriate test limits are applied.

The details of the test equipment used are also recorded at the top of the form

together with the calibration date. This information is important for traceability sincetest results can only be proved to be accurate if it can be demonstrated that the testequipment was in calibration.

The visual inspection checklist provides a record that the relevant parts of the

equipment have been inspected. This is very important since, in practice, the visualinspection is likely to flag up problems far more often than the electrical safety teststhemselves. It is also important that a record of visual inspection is kept. Where user

organisations use electronic means to record data downloaded from electrical safetytesters, it is important to add information on visual inspection to the record.

The electrical safety tests that are used in this particular protocol are few in numberand are the same tests, derived from IEC60601-1, that were selected for HEI 95. Theearth continuity test is obviously important for all class I equipment. The insulation

test is intended to look at the insulation between the mains part and the earth of the

equipment under test, and may be regarded as a pre-test to verify that it is safe toapply mains power in order to measure leakage currents.

Earth leakage current here is only measured under normal condition (NC). Note that"normal" and "reverse" here mean that the leakage current is measured with L1 and

L2 the right way round and the wrong way round. Both of these conditions are defined

as "normal condition". This test will not usually produce as high a reading as if the testis conducted with under single fault condition, neutral open circuit. However, in most

cases, if there is no problem with earth leakage current under normal condition, thereis unlikely to be one under the single fault condition.

Enclosure leakage and patient leakage currents are both recommended under this

protocol to measured under single fault condition, earth open circuit (EOC). Therationale behind this is that any problems are likely to be evident under this condition

and it is not improbable that the fault condition may arise when the equipment is inuse.

At the foot of the form, it is recorded whether the equipment has passed or failed in

the light of the visual inspection and the electrical safety test results. The date of thetest and the identity of the person who performed the test must also be recorded.

The comments field below the table is a useful feature of any recording system. It

allows any observations to be recorded, for example, of peculiarities of the equipmentunder test or concerns about test results. The record should be referred to by the

person performing the next test and inspection on the equipment prior to carrying outthe inspection and test.


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General points on safety


Many electrical safety tests are performed under single fault conditions such that ameans for protection against electric shock has been removed. In the case of patientleakage current with mains on applied parts, a hazard is actually introduced.

Even under normal condition, the equipment under test cannot be regarded as safe,since the supplementary protection may have been compromised by the test

arrangement. For these reasons no equipment under test should be touched whilsttests are being undertaken, as parts of the equipment may be hazardous live. For

similar reasons, tests should be conducted on suitable non-conductive surfaces andconductive objects should be kept well clear of the equipment.

The potential hazard is exacerbated by the use of automatic testers when running in

automatic or semi-automatic modes since hazardous voltages may appear on theequipment under test at any time without any warning. Where it is not possible to

remove equipment to a workshop facility for testing, particular care must be taken toensure that there is no possibility of any other persons coming into contact with the

equipment under test.

Many categories of medical electrical equipment can produce outputs for treatmentpurposes that, if applied incorrectly to a person can prove fatal, or at least cause

serious injuries. Examples of these categories include surgical diathermy machines,nerve and muscle stimulators, short-wave therapy units and defibrillators. Persons who

have not had specific training on such equipment sufficient to enable them to avoid thehazards should not be allowed to perform electrical safety testing on it.

The tests applied in the course of routine safety testing can cause damage to

equipment if carried out incorrectly or inappropriately. Such damage may lead directly

or indirectly to patient injuries or death if the equipment is put back into service in this

condition. It is clear that only maintenance personnel who are sufficiently trained toavoid such occurrences arising should carry out electrical safety testing of medicalequipment.

Bibliography


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Bibliography

Reference has been made to the following documents in the preparation of thesenotes.

BS 5724 Part 1: 1989/IEC601-1:1988 - British Standard - Medical electricalequipment - Part 1. General requirements for safety

IEC 60601-1 Third edition: 2005 - International standard - Medical electricalequipment - Part 1: General requirements for basic safety and essentialperformance

Health Equipment Information Number 95 (HEI95) August 1981: Code ofpractice for acceptance testing of medical electrical equipment (withdrawn Dec

1999)

MDA Device Bulletin DB9801 Supplement 1: December 1999 - Checks and testsfor newly delivered medical devices (replaced November 2006)

MHRA Device Bulletin DB2006(05): Managing Medical Devices - Guidance forhealthcare and social services organisations

HSE memorandum of guidance on the Electricity at Work Regulations 1989(ISBN 0-11-883963-2)

IEE Code of Practice for In-service Inspection and Testing of ElectricalEquipment (ISBN 0-85296-776-4)

Electrical Safety of Medical Equipment

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