Most employers are aware of the risks of working on or near live electrical components. Electric arc flashes when two electrodes connect by a luminous bridge, leaping across the void. Arcs can occur on a small scale as electrical short circuits. The more worrying consequence can be an electrical arc flash. This is when a one off flash occurs with temperatures of over 10,000 degrees Celsius. At this temperature the risk of a severe injury or even fatality is extreme high. Water boils at 100 degrees centigrade, metals can melt at 600 degrees but these potential temperatures can be hotter than the surface of the sun.
Who is at risk? The reason this risk may be under estimated may be that it faces a more limited range of activities and professions. The main industries where the risks may occur are in the electrical utilities installation, electrical engineering in industry, the rail industry and civils.
Should an arc occur the effects can be catastrophic for the individual, those nearby, the building, electrical infrastructure and even the organisation as a whole. An arc flash will normally set fire to clothing worn, resulting in severe burns even to skin protected by clothing or PPE. The intensity of the flash occurs in an instant, the flash may only occur for a spilt second but may travel many metres into the surrounding area. The extreme temperatures may also set fire to any combustible materials nearby which may lead to the fire spreading even further after the initial flash.
When an arc occurs there will be a bright flash with ultra violet or infra-red light resulting in instant temporary or even permanent blindness. Hot metal parts heated by the short circuit can melt and vaporise. As metals vaporise they rapidly expand in size and may explode, leading to a pressure wave which may heat those nearby and throw them across the floor. They may fall if working at height or be thrown at high velocity against other dangerous surfaces. The noise from the explosion can result in hearing damage as well as with projectiles being ejected in a variety of directions.
The Electricity at Work Regulations 1989 establish clear standards which require employers to take steps to ensure “All electrical systems must be constructed and maintained, so far as is reasonably practicable, to prevent danger.” Regulation 4 requires that when evaluating the suitability of the construction of electrical systems, several factors should be considered, including:
- Manufacturers’ recommendations
- Likely load and fault conditions
- Need for suitable electrical protection devices such as overload protection
- Environmental conditions which may affect the mechanical strength and protection required
The management of any work, where there may be a risk of an electrical arc, needs to be managed properly but there is no fail proof way of protecting employees from electrical arcs. The first important control is to ensure all relevant staff are fully trained to ensure they can prevent any arcs from occurring. Training includes the risks, work methods, the use of the right equipment and the wearing of PPE. For those at risk there are a variety of electrical arc protective clothing and equipment which can assist preventing the incidents from occurring, therefore limiting serious injury and the potential for fatalities.
However it is very important that PPE, if it is worn, is to the right standard and worn correctly. Just having a jacket or top unzipped because the worker has become hot would mean they are not protected if a flash were to occur. There are arc flash vests which can be worn which do not have the facility to be opened by the wearer. Jackets, vests and trousers are normally manufactured with layers of different materials to provide a flash resistant garment. Some can be waterproof, splash proof, high visibility or even thermal.
The wrong garment or wearing one which is damaged will not provide the protection. Garments can normally be washed and cleaned but again this must be done at the right temperate setting, normally 60 degrees centigrade, to ensure any of the protective layers are not damaged.
Employers need to ensure that their electrical systems are installed, designed and maintained to the right standard. The maintenance of electrical systems needs to be carried out periodically in a systematic fashion and based on an appreciation of the risks posed by each electrical system.
A thermal imager provides a visualisation of heat, often invisible to the naked eye, which provides a quantitative analysis of temperature rise. A thermal imager can display and record temperature differences as low as 0.3°C which is far above the sensitivity required to detect electrical faults. A warm wire in a bundle of wires or amongst hundreds of terminals will be immediately detected and displayed. Overheated components or components that are breaking down but look visually normal to an electrician will also be immediately apparent to a thermal imager operator.
Infrared thermography or thermal imaging is a recognised technique for detecting loose or corroded connections. A poor electrical connection under load will rise in temperature. Arcing may occur and eventually the connection will fail potentially resulting in a fire and an expensive shut-down of associated equipment or machinery.
Electrical installations must be inspected and tested by a person who has the competence to do so, such as an approved contractor from the Electrical Contractors’ Association (ECA), National Association for Professional Inspectors and Testers (NAPIT), National Inspection Council for Electrical Installation Contracting (NICEIC) .
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