Electrical safety

26 May 2009
Lessons from Losses 4/2009. For professionals, electrical safety usually means the prevention of electric shock and electric arc accidents. However, electrical fires cause more deaths. Last year in Finland, one person died in an electrical accident but several people were killed in electric fires. Of those killed by construction fires, 20% died in fires caused by electricity.

Electrical accidents in recent years

An electrician was replacing a fuse in a railway switch heating transformer.

Head Fitter, together with his partner, was assigned to replace the fuse. He requested the operational centre to switch the voltage off, but the procedure was performed on a wrong wire as a result of an outdated electrical wiring diagram. He received an electric shock when coming into contact with the voltage. (TOT* 13/06)

A cable fitter got a shock from the neutral conductor of a buried cable.

Two cable fitters were repairing damage caused by a storm to a low-voltage pole. A tree had fallen on a bundle assembled aerial cable and detached the connection cable from the pole. The neutral connector had also been ripped off its carrier cable. Apparently, the fitter had leaned on the cable as he descended from the pole. At the same time, he came into contact with the neutral connector and received an electric shock. The pole's voltage had not been switched off, and the centre's main switch was on. (TOT15/04)

A person painting the wall of a building died as the result of an electric shock.

Standing on a stepladder and painting the wall of a privately owned building, the painter probably staggered and grabbed the open, live wire that was fastened to the wall. He received an electric shock and died despite immediate resuscitation attempts. (TOT 12/03)

Four out of ten electrical accidents happen to professionals and the rest to laymen. Faulty actions and human error are the direct cause of more than half of all electrical accidents. The majority of fires caused by electricity are domestic. Often, the cause is incorrect use of an appliance, e.g. an electric cooker that has been left on or clothes hung up to dry inside a sauna. Alcohol is a contributing factor in many cases.

In 2007, Tukes' electrical safety surveillance unit received information on 67 electrical accidents in Finland, 25 of which involved professionals and 37 of which affected laymen. Accidents to professionals take place in industrial environments or the switchgear of electricity companies and usually result in a disability lasting less than 30 days. Accidents affecting laymen were usually mild, although the only death caused by an electrical accident last year in Finland happened to a layman.

How to manage and prevent risks?

Switchboard markings

Switchboard markings and updates might be lacking. In such cases voltage may be cut off from the wrong appliance during maintenance. Even changing a fuse is difficult when it has to be done through trial and error. Electricity turned off in an unplanned manner and without advance warning may alone cause damage or pose a danger.

Markings are a key factor in risk prevention. Wall sockets, dividing boxes Make sure that wall sockets and dividing boxes are intact and according to space classification. Do not install wall sockets where they are likely to be under mechanical strain. Avoid using extension sockets. An ungrounded plug may not be plugged into a grounded wall socket, nor may a plug be altered to fit the socket.

Extension cords do not replace fixed installations; extension cords should be removed when they are not needed. The structure of an extension cord may not be altered by filing or exchanging a regular plug with a grounded plug. If this is done, it is possible to plug an ungrounded extension cord into a grounded socket. The metal frame or shell of an electric appliance plugged into an extension cord may, when malfunctioning, become energized and cause an immediate, life-threatening danger.

Plug in only low-duty electrical appliances to extension cords with multiple sockets. High-duty appliances may cause overload and result in blowing fuses. Overheated electrical appliances, including extension cords, are a sign of malfunction or overloading, which create a danger of fire or accident.

Machinery and equipment

Dusty and dirty machines and equipment may heat up and pose a fire hazard. If a connection box is broken, the appliance may cause an electric shock. Check the condition of electric appliances regularly and ensure that the junctions are tight and appropriate and that the junction cord is intact. Make sure by hand that they are not too hot, thus preventing the risk of short-circuiting.

Lights

Make sure that lights are intact and clean. A light should be placed in a location where it can be repaired and serviced. Ensure that the enclosure class of the light is appropriate; when collected inside a light, dust and dirt can ignite.

Do not use a bulb that exceeds the recommended level for the lamp. Obey the safety distance marked on the light. Blinking fluorescent lights cause the light's connector device to heat up and thus create a fire hazard. When changing fluorescent lamps always change the fuse starter as well; it poses a fire hazard when worn out.

Cabling

Make sure that the cabling is intact and appropriately attached.

General tidiness and maintenance

Regular cleaning not only creates a pleasant workplace but also enhances electrical and industrial safety. While cleaning, the condition of appliances can easily be observed.

Initial fire extinguishing

There should be a sufficient amount of initial fire extinguishing equipment. Its location should be clearly marked. In addition, the extinguishing equipment should be suited for the purpose.

Compartmentation

Openings and holes created during repair work should be sealed and made fireproof immediately. Furthermore, the sealing solution for leads should be selected so that sealing can be performed as early as possible.

Automatic fire alarms and extinguishing equipment

Electrical fires usually begin with smouldering, which generates smoke. It may take a long time for the heat to build up. Therefore, electric equipment and cable rooms should be equipped with smoke detectors, which alarm at the early stages of the fire before significant damage has occurred.

Large and/or important electric equipment and cable rooms should be equipped with automatic fire extinguishing equipment. Usually, gas-extinguishing equipment is the most appropriate type, but water sprinklers are also suitable, especially for cable rooms.

Contracting electric work and documentation

When contracting electric work, make sure that your fitter is qualified and authorised to perform electric work. Furthermore, ensure that you receive the appropriate documents for the electric work performed and, if necessary, the minutes of the commissioning inspection. Lack of notes, blueprints or switchboard diagrams causes problems when additions are made at a later point.

Live working

Usually, electric work is performed on a dead target, i.e. the target is disconnected from the voltage from all directions, reliably preventing it from being switched on during work in progress. Check that the target is dead when beginning the work and when continuing after a break. After the work is completed, the voltage can be switched on once confirmed that it is safe to do so.

Live work is allowed under certain, very specific conditions and only a person trained for such tasks may perform it. There should be written instructions for the work, and live working tools and equipment must be used.

Jaana Salo

* The surveillance system (TOT) investigates occupational accidents that have resulted in a fatality.