Electricity is essential to modern day living and working. It can be supplied to plant and equipment by battery, mains or generator. It is a hazard that needs to be controlled.
Electricity can cause:
- Electric shock – results in muscle contraction and can disrupt breathing and the heart. A very low current (30 mA) across the heart can be fatal in a short time (fraction of a second);
- Ignition source.
With alternating currents people can involuntarily grip onto a conductor, which increases the time of exposure. Also, getting an electric shock can cause people to jump back, possibly leading to a fall (including from height) resulting in other injuries.
Issues with electricity voltage
It is the current that kills, but the voltage of the supply that causes the current to flow. Most batteries operate at low voltages and do not have the potential to cause electric shock (unless many are wired in series to create a high voltage).
So called 110V systems are often used for work equipment (in the UK they are supplied with yellow plugs). They are a 110V alternating current (AC) with centre tapped earth. No electrocutions have been known with this arrangement.
Standard UK mains is 230V AC. This can cause fatal electrocution. Industrial facilities may have significantly higher voltage supplies and users, and so require particular care and control.
Protecting people from electricity
The first consideration for protecting people is whether a low voltage system can be used (e.g. battery or 110V). This significantly reduces the potential for harm but it is important to remember that these can still act as an ignition source. Also, they are likely to require a higher voltage supply at some point (e.g. mains to charge or provide supply to step down to 110V).
Other ways to protect include:
- Use of double insulated equipment – these have extra layers of insulation to prevent contact with live conductors;
- Fuses that ‘blow’ if excess current flows;
- Residual circuit devices that trip if current differs significantly between live and neutral;
- Earthing conducting parts so they cannot become live. Also, if there is a fault and there is low resistance in the earth a large current will be drawn that will blow fuses or trip a RCD;
- Bonding conducting parts so that they keep the same voltage and so do not create differential.
Safe use of electrical equipment
When using electrical equipment it is important to ensure that:
- The correct equipment is used for the job;
- Equipment is in good order;
- Cables are in good condition;
- Connections are to a correctly rated supply;
- Plugs are properly wired and secured;
- Correct fuses are in place.
Only equipment designed for harsh environments should be used in them. These include damp, dust and vapour.
Portable appliance testing
A portable appliance test (PAT) is a recognised set of tests of earth and insulation. It is recommended for any equipment working above 50V that is earthed or does not meet the standards for double insulation.
PA tests must be carried out by a competent person. The frequency of re-testing varies between 1 and 5 years.
Reference – ‘Maintaining portable electrical equipment in offices and other low-risk environments’ available free at http://www.hse.gov.uk/PUBNS/indg236.pdf
Working on electrical systems
Anyone maintaining, repairing or interfering in some way with electrical equipment needs to be competent. Broadly speaking levels of competence are defined according to voltage (i.e. someone competent on low voltage may not be competent to work on high voltage).
Ideally the electrical supply will be positively isolated before potentially live conductors are exposed. Special precautions are required where isolation is not possible or cannot be proved. Permit-to-work systems are often used so that work cannot start until isolation has been achieved or alternative risk control measures implemented.
First aid following electrocution
The following should be carried out if someone is electrocutes, with the steps carried out in the order stated:
1. Summon help (999);
2. Isolate supply;
3. If it is not possible to isolate, move the casualty using non-conducting pole or similar;
4. Once the person has been detached from the supply, treat as per symptoms (breathing, heart).
The Electricity at work regulations 1989 are mostly directed at hardware requirements. Installations are required to be of proper construction; conductors must be insulated or other precautions taken; there must be means of cutting off the power and means for electrical isolation.
Reference – ‘Electrical safety and you’ available free at http://www.hse.gov.uk/pubns/indg231.pdf
Reference – ‘Memorandum of guidance on the Electricity at Work Regulations 1989’ available free at http://www.hse.gov.uk/pubns/priced/hsr25.pdf