Unit GC 2 – Controlling workplace hazards Element 5: Electrical safety

Question 1

Identify the main hazards associated with electricity

Answer 1

• Electrical burns (direct and indirect)
• Electric shock
• Arcing
• Fire
• Explosions

Question 2

List 5 factors that would determine the severity of an electric shock.

Answer 2

1. Size of the current (I)
2. Electrical resistance of the skin (R)
3. The pathway through the body
4. The amount of time in contact with the conductor
5. The frequency of the current (Hz)

You could also include

• Voltage
• Current path through the body
• Speed of first aid treatment

Question 3

The effects that an electric shock can have on the body.

Answer 3

• Damage to the nervous system
• Fibrillation of the heart (heart ‘flutters’ and does not pump)
• Internal burns along route of current flow
• External burns at entry and exit points
• Muscular contractions causing tears
• Stoppage of breathing
• Heart stops and subsequent death

Question 4

The difference between direct and indirect electrical burns.

Answer 4

Direct burns are caused by an electrical current passing through the body. This could be by coming into contact with a live conductor whilst working on an electrical circuit.

Indirect burns are caused when, typically, a short circuit heats up an object and that object is then touched. An example would be shorting a spanner across the terminals of a vehicle battery and then trying to take it off with bare hands.

Question 5

Outline 8 common causes of electrical fires

Answer 5

1. Unsafe electrical installations
2. Lack of maintenance and testing of fixed installations
3. Overloading sockets
4. Damaged cables, plugs and sockets on portable equipment
5. Poorly maintained portable appliances
6. Static electric in flammable atmospheres
7. Using inappropriate equipment in flammable atmospheres
8. Use of inappropriate fuses in equipment

Question 6

Secondary hazards that may be introduced as a result of using electrical equipment.

Answer 6

• Involuntary movement of body which could lead to falls
• Accidentally energising equipment
• Cutting off power to safety and security devices
• Computer shutdown causing production interruption with possible safety implications

Question 7

Factors that should be considered when deciding on the suitability of electrical equipment

Answer 7

• Is it suitable for the work to be carried out
• Is it suitable for the working environment
• Is it rated at an appropriate voltage for the conditions
• Is it built to a recognised standard
• Is it free from defect and properly maintained

Question 8

The purpose, merits and limitations of different electrical protective devices:

Answer 8

Fuses

Act as a weak link in the circuit designed to melt and stop current flow in overload conditions.

Merits – cheap and easily replaced.
Limitations – does not protect against shock; relatively slow in operation.

Earthing

Earthing provides a low resistance path to earth in the event of a circuit fault.

Merits – may prevent indirect shock by preventing metal fixtures from becoming live.
Limitations – may become ineffective if not maintained.

Isolation

Achieved by disconnecting and separating the electrical equipment from the source of electricity.

Merits – as there is a gap between the source of electricity and equipment this method provides the safest option.
Limitations – may make other equipment ‘dead’; does not allow live fault finding to be carried out.

Question 9

Reduced voltage systems

Answer 9

By reducing the voltage used to power equipment, the consequences of electrical shock can be greatly reduced. This can be achieved by using:

Question 10

Reduced voltage transformer and equipment.

Answer 10

Merits – potential shock voltage is reduced to 55v reducing the chance of severe injury.
Limitations – equipment expensive and heavy; power supply to transformer still at mains voltage.

Question 11

Battery powered tools

Answer 11

Merits – little risk of shock if used properly; no trailing cables.
Limitations – loss of power; still need to charge batteries therefore contact with mains voltage.

Question 12

Residual current devices

Answer 12

Works by comparing the current flowing from the RCD to the current flowing back. If the RCD detects a change in flow above a set current (typically 30mA) over a period of time (20mSec) the RCD will trip and cut off the current.

Merits – very sensitive; protects from severe shock.
Limitations – sensitivity may cause spurious tripping; cannot be set if internal wiring fault (this might be seen as an advantage).

Question 13

Double insulation

Answer 13

Achieved by method of manufacture. Potential live parts of electrical equipment are surrounded by two separate layers of insulation therefore preventing the external casing of the equipment from coming live.

Merits – does not need earth wire.
Limitations – may become live if casing becomes damaged.

Question 14

Inspection and maintenance strategy for electrical systems

Answer 14

Portable appliances (3 stage approach)

1. User checks - operator
2. Formal visual inspection – appointed person
3. Combined test and inspection – competent person

Fixed installations - competent person

Question 15

Inspection frequencies, as laid down in the Electricity at Work Regulations for:

Answer 15

Fixed wiring

Fixed wiring within premises should be subject to 5 yearly electrical integrity tests.

Fixed electrical equipment

Electrical systems should be checked as part of the planned maintenance of the equipment.

Question 16

Portable electrical equipment (visual inspection and PAT)

Answer 16

• Frequency depends on type of equipment, how it is used and where it is used.
• Hire equipment must be PAT tested before every hire regardless of length of hire.
• Heavy use equipment in harsh environments may be inspected weekly and PAT tested 3 monthly.
• Double insulated equipment may be inspected between 1 – 3 years and never need PAT testing.

Question 17

Outline the issues to be considered during a user check of portable electrical equipment.

Answer 17

• Is there a current PAT sticker attached?
• Are bare wires visible?
• Is the cable in good condition?
• Is the plug in good condition? Are there signs of blackening?
• Are there are any non-standard (Unsafe) joints?
• Is the outer covering of the cable gripped where it enters the plug or equipment?
• Is the casing of the equipment in good condition?
• Is the cable the correct length?

Question 18

Identify what is meant by ‘competent’ in this context.

Answer 18

People working with electricity should possess:

• Knowledge of electricity
• Experience of electrical work
• An understanding of the system and practical experience of that class of system
• Understanding of the hazards and their precautions
• Ability to recognise whether it is safe to continue work.

Question 19

Outline the factors to consider when determining the frequency for the inspection and testing of electrical equipment.

Answer 19

Factors to be considered include the type of equipment - whether portable or fixed and its voltage; the integrity and age of the equipment including the likelihood of it becoming damaged and the frequency and duration of its use; the environment in which it is to be used; its previous maintenance and repair history; and any recommendations made by the manufacturers or in guidance published by enforcement agencies or health and safety bodies.

Make sure your answer covers both portable appliances and fixed electrical installations or plant. This question was not just checking your understanding of PAT testing requirements.

Question 20

With reference to an electrical circuit, state the relationship between voltage, current and resistance.

Answer 20

The voltage (V), the current (I) and the resistance (R) are linked by a simple relationship called Ohm’s Law.

Question 21

With respect to use of portable electrical appliances, identify examples of faults and bad practices that could contribute to electrical accidents.

Answer 21

1. Misuse of equipment such as carrying around site using the cable
2. Inappropriate equipment for the environment / task
3. Inappropriate joints in cables
4. Faulty cables and casing
5. Lack of inspection and maintenance

Question 22

Outline the three levels of inspection that should be carried out to ensure the safety of portable electrical appliances.

Answer 22

1. User Checks

This can be done by the person using the piece of electrical equipment. User inspection training can be incorporated into basic equipment usage training. With a recorded method of logging faults or necessary repairs, electrical equipment can be kept in safe working order, and most electrical risks can be controlled.

2. Formal Visual Inspection

This should be conducted by a qualified competent person, testing will usually involve a visual inspection and a more involved inspection of the equipment to check for signs of potential faults or risks.

3. Combined Test & Inspection

This should be carried out by a competent person at set intervals determined by the level of risk presented from use of the equipment. It includes the checking of the appliance with regard to fuses, connections and polarity. The second part of the inspection is the portable appliance testing which includes the use of a portable appliance tester providing a pass / fail test result.

Question 23

The main causes of electrical accidents are:

Answer 23

• people working on ‘live’ equipment, thinking it is ‘dead’
• People knowingly working on ‘live’ equipment without:
• adequate training
• appropriate equipment
• adequate precautions

Question 24

Main factors affect the selection and suitability of electrical equipment including:

Answer 24

• the suitability for the work to be carried out
• the suitability of the equipment for the working environmental
• the rating at the required voltage for the site conditions such as 110V
• built to a recognized standard and capable of being isolated in an emergency
• free from defect and properly maintained

Question 25

There are a number of high risk work situations associated with the use of electricity. These include:

Answer 25

• working with poorly maintained electrical equipment
• using electrical equipment in wet environments due to work processes or weather
• working on or near overhead power lines.
• work on and around excavations resulting in possible contact with underground services
• work on mains electrical equipment

Question 26

Ensure works in the vicinity of overhead lines are strictly controlled. Risk control measures to be used include:

Answer 26

• dependent on the type of work to be carried out it may be necessary to divert or ‘make dead’ overhead cables
• live work under cables must be carried out under a permit to work
• mark the presence of the cables with ‘goal posts’
• ensure mobile work equipment in kept a minimum horizontal distance from cables

Question 27

If an electrical incident occurs in the workplace there must be a procedure in place that is well understood by all employees. The procedure should include the following:

Answer 27

• summon help
• isolate electrical supply / remove casualty from source
• administer first aid
• CPR if necessary
• place casualty in the recovery position
• monitor until medical help arrives

Question 28

There are many national laws which forbid live working on electrical systems unless there are no other options possible other than live working. Where this is the situation the organisation will be required to use a safe system of work in order to reduce the risk of injury/harm. The safe system of will include:

Answer 28

• use of a permit to work system
• use of competent persons
• provision of suitable tools and equipment
• isolation of area

Question 29

Ensure all work activities around excavations are strictly controlled. Risk control measures to be used include:

Answer 29

• the use of service drawings to identify services
• the use of locating device to assist marking the services location on the ground
• issue of a permit to dig and authorise work to be carried out
• excavation of trial holes to confirm to location of services
• the use of safe hand digging techniques

Question 30

Outline the precautions to protect against electrical contact when:

Answer 30

a) Digging near underground cables

Ensure all work activities around excavations are strictly conrolled. Risk control measures to be used include:

• the use of service drawings to identify services
• the use of locating device to assist marking the services location on the ground
• issue of a permit to dig and authorise work to be carried out
• excavation of trial holes to confirm the location of service
• the use of safe hand digging techniques

b) Working under overhead power lines

Ensure works in the vicinity of overhead lines are strictly controlled. Risk control measures to be used include:

• dependent on the type of work to be carried out it may be necessary to divert or ‘make dead’ overhead cables
• live work under cables must be carried out under a permit to work
• mark the presence of the cables with ‘goal posts’
• ensure mobile work equipment is kept a minimum horizontal distance from cables.