Technical Article

Electrical Safety Awareness

Electrical Safety Awareness: Accidents and Fires 

One would suspect that electrical industry workers are more likely to have an accident involving electricity than any other group but in fact only 25% of electrical accidents involve these people. Other trade workers, contractors and members of the public making up the other 75% and in the domestic situation the most common cause of electrical accident is attributed to faulty flexible cords and plugs. 

 

The degree of risk associated with electric shock is difficult to assess and despite a precise relation between cause and effect there are so many different factors and circumstances around each individual case of accidental contact with a live conductor that the ultimate outcome is difficult to determine. The current necessary to produce a fatal shock is very small about 20 milliamps with the most dangerous path being through the region of the chest either from one hand to another or from a hand to the feet. 

The effect on the heart from even a minor shock of short duration can cause fibrillation or the loss of muscular control that stops breathing or contraction of muscles. It can also prevent letting go of the conductor and usually resulting in deep seated burns. The supply voltage is one of the factors which governs the amount of current (amperes) that flows and for that reason the lower the voltage the lower the severity of electric shock. 

The incidence of electric shock amongst electrical tradesmen when compared with other occupations is low and the injuries that do occur are generally associated with large-scale electric arcs. Other tradesmen more commonly receive an electric shock when using defective portable equipment in unsafe circumstances. Usually without the use of an isolating transformer or residual current device. More recent safeguards include double insulated tools, monitored earthing systems and extra low voltage power tools. 

Overhead lines need to be treated with respect and electrical accidents involving fencing wire, yacht masts, mobile cranes, scaffolding, tree trimming and painting tools in contact with overhead electrical conductors have proved fatal in the past. Often fires recorded and attributed as electrical in origin are actually more often the result of accidental misuse or faulty equipment. The true cause actually being localised heat raising flammable materials to their ignition temperature. 

Heating appliances are the most common, but it is often forgotten that an ordinary incandescent lamp distributes 90% of its energy in the form of heat and if this is not allowed to escape, temperatures capable of igniting flammable materials easily develop. Localised heating can also occur at a point of abnormally high electrical resistance (ohms) and any loose connection will cause a rise in temperature which in turn and overtime causes oxidation, increased resistance and subsequently more heat sufficient to eventually ignite materials in close proximity. 

Fires that originate at sockets and switches in general are the result of overheating for a long period of time with the signs being ignored or going unrecognised. For that reason any smell of overheated insulation, that distinct pungent odour, or any sensation of warmth to the touch when removing electrical plugs from a socket are danger signals that must be investigated. Electrical fires are not as common as we would like to think and those that do occur are often the result of incorrect use of equipment or a general lack of maintenance.