Electrical safety Flashcards by Lydia Osborne | Brainscape

Q

In micro shock

the current is too small to be harmful

A

False

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Q

In micro shock

The frequency of the current is not important

A

False

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Q

In micro shock

The right ventricle is more sensitive than the left

A

True

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Q

In micro shock

the current must be greater than 100uA

A

True

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Q

In micro shock

The current may induce asystole

A

False

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Q

In electric shock

The current is too small to be harmful

A

False

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Q

In electric shock

The effect depends on the duration of current flow

A

True

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Q

In electric shock

current mainly affects the flexor muscles

A

False

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Q

In electric shock

effect depends on the total amount of energy delivered

A

True

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Q

In electric shock

electrons flow through the body

A

False

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Q

The electricity supply to an operating theatre

Is a three phase supply

A

False

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Q

The electricity supply to an operating theatre

consists of live, neautral and earth wires

A

False

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Q

The electricity supply to an operating theatre

Has a voltage of approx 240V

A

True

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Q

The electricity supply to an operating theatre

Has an Earth connection from the substation

A

False

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Q

The electricity supply to an operating theatre

Varies sinusoidally at 50Hz

A

True

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Q

Electrostatic interferance from a piece of equipment:

Requires a current to flow in the power wires

A

False

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Q

Electrostatic interferance from a piece of equipment:

Is easily prevented by using screened cable

A

True

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Q

Electrostatic interferance from a piece of equipment:

Is reduced by insulating the signal leads

A

False

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Q

Electrostatic interferance from a piece of equipment:

is minimised at high frequencies

A

False

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Q

Electrostatic interferance from a piece of equipment:

Is halved by doubling the separation between signal and power leads

A

True

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Q

Electromagnetic interference:

Requires the source of the interference to be drawing current

A

True

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Q

Electromagnetic interference:

with an ECG monitor can be prevented by using screened leads

A

False

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Q

Electromagnetic interference:

Is halved by doubling the separation between signal and power leads

A

False

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Q

Electromagnetic interference:

does not affect battery powered equipment

A

False

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Q

Electromagnetic interference:

May be caused by a transformer

A

True

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Q

Requirements of an earth connection:

Resistance must be less than 0.5 ohm

A

False

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Q

Requirements of an earth connection:

Leakage current must be less than 0.5mA (type 1 equipment)

A

True

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Q

Requirements of an earth connection:

Its connection at the substation must be tested regularly

A

False

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Q

Requirements of an earth connection:

Must be capable of carrying a current of 25A

A

True

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Q

Requirements of an earth connection:

Surge test must be performed at 240V

A

False

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Q

The star point:

Is the Earth connection at the electrical substation

A

True

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Q

The star point:

Is connected to the neutral wire at the electrical substation

A

True

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Q

The star point:

Carries electric current back to the power station

A

False

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Q

The star point:

Protects the user from the effects of a lightening strike

A

True

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Q

The star point:

is not used in a three phase electricity supply

A

True

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Q

An earth free supply:

Increases electrical safety

A

True

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Q

An earth free supply:

Provides reduced protection from electric shock

A

False

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Q

An earth free supply:

Has line and neutral connections

A

False

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Q

An earth free supply:

is required for type II equipment

A

False

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Q

An earth free supply:

removes the need for a local earth connection

A

False

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Q

The line isolation monitor:

Is required by an earth free supply

A

True

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Q

The line isolation monitor:

Generates an alarm if too much current is drawn

A

False

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Q

The line isolation monitor:

switches off the supply when an electric shock occurs

A

False

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Q

The line isolation monitor:

chesck that more than one phase are not connected together

A

False

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Q

When considering electricity:

Electrons move at lose to the speed of light

A

False

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Q

When considering electricity:

alternating current has a mean amplitude of zero

A

True

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Q

When considering electricity:

For a single phase mains supply the peak voltage is plus minus 250V

A

False

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Q

When considering electricity:

direct current is easier to switch than alternating current

A

False

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Q

When considering electricity:

current can be dissipated by and earth connection

A

False

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Q

In an electrical transformer

The efficiency is approx 60%

A

False

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Q

In an electrical transformer

Electrons are transferred between its primary and secondary windings

A

False

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Q

In an electrical transformer

changing the turns ratio can increase or decrease the output voltage

A

True

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Q

In an electrical transformer

When voltage is halved, the maximum current available is halved

A

False

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Q

In an electrical transformer

An earth connection increases efficiency

A

False

Q

Electrical burns:

Are caused by direct current

A

True

Q

Electrical burns:

are concentrated in deep tissues

A

False

Q

Electrical burns:

The size depends on the voltage applied to the tissues

A

True

Q

Electrical burns:

depend upon the size of the current passed

A

True

Q

Electrical burns:

Only occur if the frequency is less than 100KHz

A

False

Q

Electrical skin resistance to direct current defibrillation

decreases as paddle surface increases

A

True

Q

Electrical skin resistance to direct current defibrillation

increases when electrode jelly is applied to the paddles

A

False

Q

Electrical skin resistance to direct current defibrillation

decreases as the energy (watt-seconds) delivered increases

A

True

Q

Electrical skin resistance to direct current defibrillation

increases as the number of shocks increases

A

False

Q

Electrical skin resistance to direct current defibrillation

decreases with an increase in paddle pressure

A

True

Q

Direct current:

flows in one direction

A

True

Q

Direct current:

is constant in magnitude

A

False

Q

Direct current:

Can be produced from alternating current

A

True

Q

Direct current:

Is not harmful to the tissues

A

False

Q

Direct current:

Will cause electrostatic interference

A

False

Q

When considering the classification of electrical equipment:

Type II apparatus requires an earth connection

A

False

Q

When considering the classification of electrical equipment:

The maximum earth leakage for type B(F) equipment is 500uA

A

True

Q

When considering the classification of electrical equipment:

Type I equipment is internally powered

A

False

Q

When considering the classification of electrical equipment:

For type C(F) equipment the (F) signifies Earth fre

A

False

Q

When considering the classification of electrical equipment:

Type III equipment may be used whilst charging

A

False

Q

The fuse in the electrical supply to medical equipment:

should be replaced after 1000 hours service

A

False

Q

The fuse in the electrical supply to medical equipment:

should be of the quick blow type

A

False

Q

The fuse in the electrical supply to medical equipment:

Provides protection from electric shock

A

True

Q

The fuse in the electrical supply to medical equipment:

If placed in the neutral wire enhances electrical safety

A

False

Q

The fuse in the electrical supply to medical equipment:

Can be replaced by an earth leakage circuit breaker (RCCD)

A

False

Q

When considering the electrical supply to medical apparatus:

The local earth wire is brown

A

False

Q

When considering the electrical supply to medical apparatus:

the line wire is red

A

False

Q

When considering the electrical supply to medical apparatus:

The fuse should be chosen to limit leakage current to a safe value

A

False

Q

When considering the electrical supply to medical apparatus:

2 pin plugs avoid the risk of earth leakage

A

False

Q

When considering the electrical supply to medical apparatus:

Use of an extension lead compromises electrical safety

A

True

Q

Type III apparatus:

Require three wires, line, neutral and earth

A

False

Q

Type III apparatus:

the earth leakage current must not exceed o.5mA

A

False

Q

Type III apparatus:

must not be directly connected to a patient

A

False

Q

Type III apparatus:

Can not act as the source of leakage current to a patient

A

True

Q

Type III apparatus:

must have a fuse of less than 1Amp

A

False

Q

The following statements are correct regarding basic electrical quantities and units
the coulomb is a unit of electrical charge equivalent to 6.24 x 10^18

A

True

Q

The following statements are correct regarding basic electrical quantities and units
the coulomb is a base SI unit

A

False

Q

The following statements are correct regarding basic electrical quantities and units
A 3 kW electrical appliance (running on UK mains voltage) would require a 5 amp fuse

A

False

Q

The following statements are correct regarding basic electrical quantities and units
The definition of 1 ampere is the flow of 1 coulomb of charge per second through any crossdirectional area of the conductor

A

True

Q

The following statements are correct regarding basic electrical quantities and units
The resistance of a conductor is a constant value that is not influenced by other factors

A

False

Q

The following statements are correct regarding capacitors and their capacitance:
Capacitors used in defibrillators typically have a capacitance of breater than or equal to 1 farad

A

False

Q

The following statements are correct regarding capacitors and their capacitance:
increasing the distance between the plates of a capacitor increases its capacitance

A

False

Q

The following statements are correct regarding capacitors and their capacitance:
the introduction of a dielectric between the plates increases the capacitance

A

True

Q

The following statements are correct regarding capacitors and their capacitance:
The stored energy of a capacitor is given by the formula E=1/2QV^2

A

False

Q

The following statements are correct regarding capacitors and their capacitance:
Capacitors can be directly charged using alternating current

A

False

Q

An earth free supply (or floating circuit):

Increases electrical safety

A

True. The supply is not earth referenced. The isolating transformer means that the 240 V supply is no longer connected to the substation, current can therefore not flow through you, via the ground to complete the circuit.

Q

An earth free supply (or floating circuit):

Provides reduced protection from electric shock

A

False. An earth free supply increases protection from electrical shock.

Q

An earth free supply (or floating circuit):

Has live and neutral connections

A

False. Since neither supply wire is connected to ground at the substation there is no ‘neutral’ wire.

Q

An earth free supply (or floating circuit):

Is required for Type II equipment

A

False. An earth free supply is not required by Type II equipment.

Q

An earth free supply (or floating circuit):

Requires a line isolation monitor

A

True. An earth free supply does require a line isolation monitor to warn you if a fault has compromised safety of the system.

Q

Concerning electrical safety:

Ohm’s law states that resistance is inversely proportional to current for a given voltage

A

True

Q

Concerning electrical safety:

Wet skin increases the likelihood of electrical shock from faulty equipment

A

True. Moisture reduces the impedance of skin, increasing the current that flows for a given voltage, and therefore increases the likelihood of electrical shock from faulty equipment.

Q

Concerning electrical safety:
Class 1 equipment reduces the risk of electrical shock by providing a low resistance earthed path through which leakage currents may flow

A

True. Class 1 equipment reduces the risk of electrical shock by providing a low resistance earthed path through which leakage currents may flow.

Q

Concerning electrical safety:
The no-let-go threshold occurs at
5 mA

A

False. The no-let-go threshold is the current at which the strength of the flexor muscle contraction (which is stronger than the extensors’) would prevent you from letting go of a live wire. This threshold occurs at about 15 mA.

Q

Concerning electrical safety:
Microshock can occur at currents of
20 μA

A

False. Microshock is unlikely to occur below 44 μA

Q

Concerning electrical safety:
All class 1 and 2 equipment is earthed

A

False. Class 1 equipment standards require that all components with which the user may come into contact are earthed. Class 2 equipment is not earthed, but is ‘double insulated’.

Q

Concerning electrical safety:

UK mains supply has a peak voltage of 240 volts

A

False. 240 V is the average (actually the ‘root mean square’) voltage. The voltage oscillates between +/- 340 V.

Q

Concerning electrical safety:

A current of 100 mA passing across the myocardium is often sufficient to induce ventricular fibrillation

A

True. A current of near 100 mA passing across the myocardium is often sufficient to induce ventricular fibrillation.

Q

Concerning electrical safety:

An earth lead eliminates the chance of electrical shock from electrical apparatus

A

False. The amounts of leakage current passing through the earth wire and an individual in contact with a faulty piece of apparatus is proportional to their resistances.

Q

Concerning electrical safety:

A typical medical infusion pump is rated ‘BF’, i.e. suitable for connection to the body

A

False. Typical medical infusion pumps are rated ‘CF’, so they are suitable for direct connection to the heart, because they may be connected via a column of electrolyte solution to the right atrium.

Q

Regarding the classification of electrical equipment:

Type II apparatus requires an earth connection

A

False. Double insulated apparatus has two physical barriers between the electrically applied part (the part of the apparatus connected to the mains) and the user.

Q

Regarding the classification of electrical equipment:

The maximum earth leakage current for type BF equipment is 500 μA

A

True. In BF Type I equipment, the leakage current must not exceed
0.5 mA (500 μA).

Q

Regarding the classification of electrical equipment:

Type I equipment is internally powered

A

False. Type III equipment is internally powered.

Q

Regarding the classification of electrical equipment:

For type CF equipment the ‘F’ signifies earth free

A

False. The F suffix states that the patient applied part is ‘floating’, i.e. it is electrically isolated from the rest of the apparatus.

Q

Regarding the classification of electrical equipment:

Type III equipment may be used whilst charging

A

False. Type III equipment is ‘internally powered’, if connected to an external power supply whilst charging it is no longer internally powered and the classification would change to that of the charger.

Q

Type III apparatus:

Requires three wires: live, neutral and earth

A

False. Type III apparatus is internally powered.

Q

Type III apparatus:

The earth leakage current must not exceed 0.5 mA (500 μA)

A

False. Type III apparatus has no mains connection,0.5 mA is the maximum allowable leakage from Type 1 BF equipment.

Q

Type III apparatus:

Must not be directly connected to a patient

A

False. Type III apparatus can be directly connected to a patient, e.g. an internally (battery) powered nerve stimulator.

Q

Type III apparatus:

Cannot act as the source of leakage current to a patient

A

True. Type III apparatus has no mains connection.

Q

Type III apparatus:

Must have a fuse of less than 1 A

A

False. Type III apparatus has no mains connection.

Q

Which of the following statements are true of diathermy?

It uses high frequency alternating current in the order of 5 MHz

A

False. Diathermy uses uses high frequency alternating current up to 1 MHz.

Q

Which of the following statements are true of diathermy?

Current density at the diathermy tip determines the degree of burning

A

True. Current density at the diathermy tip determines the degree of burning.

Q

Which of the following statements are true of diathermy?

In monopolar diathermy, the same high frequency current flows through the diathermy tip as the return plate

A

True. In monopolar diathermy, the same high frequency current flows through the diathermy tip as the return plate.

Q

Which of the following statements are true of diathermy?

Bipolar diathermy does not need a separate skin electrode

A

True. Bipolar diathermy does not need a separate skin electrode because the forceps act as both tip and return plate.

Q

Which of the following statements are true of diathermy?

The diathermy cannot pass current if the return plate is incorrectly applied

A

False. Current will still flow to a poorly applied ground plate. The reduced surface area increases current density which may result in burns.

Q

Surgical diathermy:

Has a lower frequency when used for coagulation than when used for cutting

A

True. High frequency continuous oscillation is used for cutting, while bursts of lower frequency are preferred for coagulation.

Q

Surgical diathermy:

Has a higher voltage when used for coagulation than when used for cutting

A

True. Coagulation uses voltages up to 9 kV, whilst cutting uses voltages up to 1 kV.

Q

Surgical diathermy:

Should never be used in patients with pacemakers

A

False. Bipolar diathermy relies on the passage of current between two electrodes close together. This minimizes the passage of current through the body and so avoids the risk of problems with pacemakers.

Q

Surgical diathermy:

May cause explosions even when non-flammable anaesthetic agents are in use

A

True. Flammable anaesthetic agents are not the only combustible gases in theatre, and fires have been reported from surgical cleaning agents as well as explosions from gas within the bowel.

Q

Surgical diathermy:

Must always be earthed

A

False. Bipolar diathermy is not earthed. Unipolar diathermy is earthed but uses an isolating capacitor to restrict the flow of mains frequency current.