Hazard Related Topics
Electrical hazards are different from other types of hazard found in construction work in that the human senses provide no advance warning. The major risks associated with exposure to an electric current are:
- Electric Shock - The severity of an electric shock is directly related to the amount of current that passes through the body and the time it takes to pass. Lower levels may cause no more than an unpleasant tingle though it may be sufficient to cause a worker to fall from a ladder or scaffold. At medium levels it causes increased muscular tension so that anything in the grasp can scarcely be released. At high levels it can cause the heart muscles to contract irregularly and this is almost invariably fatal.
- Burns - The passage of an electric current can cause burning at the point of contact. Severe burns can occur from an electric shock without actual bodily contact. Damp and / or wet conditions add greatly to the danger from electric shock.
- Explosion - These can be caused by an electrical discharge in an atmosphere where there are certain concentrations of flammable vapours or dust.
Electrical exposure causes injuries in direct proportion to the amount of electricity and the time of exposure. It follows that any effort made to reduce the amount of electricity will also reduce the severity of the consequences of any exposure. Electrical equipment on building sites, particularly power tools and other portable equipment and their leads face harsh conditions and rough use. They are likely to be easily damaged and become dangerous. Modern double insulated tools are well protected but their leads are still vulnerable. Precautions which can be taken are:
- Where possible, use a 110 volt supply system which is centre-tapped to earth so that the maximum voltage to earth should not exceed 55 volts. This will effectively eliminate the chance of death and greatly reduce injury in the event of an electrical accident. Even lower voltages can be used for lighting systems to further reduce risk.
- If mains voltages must be used, then extra precautions should be taken. Trip devices such as residual current devices (RCDs) rated at 30 mA will be needed to ensure that the current is properly cut off if contact is made with any live part. Such devices must be treated with great care and kept free of moisture and dirt and should be tested daily by operating the test button. If permanent wiring is being installed as part of the works and it is to be fitted with a trip device it is a good idea to design this work to be done at the beginning of the project so that it can be used during the construction period.
- On sites where temporary mains cable is to be used this should be installed in such a way as to avoid damage. For instance, it should be slung at ceiling height. Where mains leads to sockets may be damaged they should be positioned where they are least likely to sustain such damage or protected inside non-conducting conduit. Electric bulbs should be protected and damaged bulbs replaced.
- Electrical systems should be regularly checked and maintained by a qualified electrician. In addition users of electrical tools and equipment should be trained to carry out daily checks on the condition of the cables, the plug and the general condition of the device. The RCD should also be tested daily by pressing the test button. Any defects detected should be reported immediately and the device taken out of service.
- In addition to user checks mains voltage systems should be checked and tested weekly by a competent electrician and the results of such tests should be recorded.
- Work in areas where there is a risk of flammable vapours such as petrol stations or petrol-chemical plants may require the use of specially designed equipment to prevent sources of ignition such as sparks or overheating. Such precautions should be specified in the Pre-construction Information for the Project and the advice of a specialist may be necessary.
- The electricity supplier should be informed of the nature, duration and likely start date of the work.
- The location of overhead lines and buried cables should be identified as part of the Health and Safety Plan and where possible overhead lines should be re-routed or the power switched off. It may be possible to site the structures away from them thus "planning out" the hazard.
- Where the use of very heavy plant using a high voltage supply is planned then close liaison with the electricity supplier is essential and specialist advice may be necessary.
This is contained in The HSE publication HS(G) 141 "Electrical Safety on Construction Sites" and is obtainable from HSE Books. Following the guidance given is not compulsory. However if you do follow the guidance the HSE believes you will normally be complying with the law. Health and safety inspectors may refer to the publication as illustrating good practice.