Electrical Hazards and the Injuries

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Electrical Hazards and the Injuries

Electricity is a safe, clean and quiet method of transmitting energy. However, this apparently benign source of energy when accidentally brought into contact with conducting material, such as people, animals or metals, permits releases of energy which may result in serious damage or loss of life. Constant awareness is necessary to avoid and prevent danger from accidental releases of electrical energy.

The principal hazards associated with electricity are:

  • Electric shock
  • Electric burns
  • Electrical fires and explosions
  • Arcing
  • Secondary hazards.

The use of portable electrical equipment can lead to a higher likelihood of these hazards occurring.

Electric Shock and Burns

Electric shock is the convulsive reaction by the human body to the flow of electric current through it. This sense of shock is accompanied by pain and, in more severe cases, by burning. The shock can be produced by low voltages, high voltages or lightning. Most incidents of electric shock occur when the person becomes the route to earth for a live conductor.

The effect of electric shock and the resultant severity of injury depend upon the size of the electric current passing through the body which, in turn, depends on the voltage and the electrical resistance of the skin. If the skin is wet, a shock from mains voltage (220/240 V) could well be fatal. The effect of shock is very dependent on conditions at the time but it is always dangerous and must be avoided. Electric burns are usually more severe than those caused by heat since they can penetrate deep into the tissues of the body.

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The effect of electric current on the human body depends on its pathway through the body (e.g. hand to hand or hand to foot), the frequency of the current, the length of time of the shock and the size of the current. Current size is dependent on the duration of contact and the electrical resistance of body tissue. The electrical resistance of the body is greatest in the skin and is approximately 100 000 ohm; however, this may be reduced by a factor of 100 when the skin is wet.

The body beneath the skin offers very little resistance to electricity due to its very high water content and, while the overall body resistance varies considerably between people and during the lifetime of each person, it averages at 1000 ohm. Skin that is wounded, bruised or damaged will considerably reduce human electrical resistance and work should not be undertaken on electrical equipment if the damaged skin is unprotected.

An electric current of 1 mA is detectable by touch and one of 10 mA will cause muscle contraction which may prevent the person from being able to release the conductor, and if the chest is in the current path, the respiratory movement may be prevented, causing asphyxia. Current passing through the chest may also cause fibrillation of the heart (vibration of the heart muscle) and disrupt the normal rhythm of the heart, though this is likely only within a particular range of currents.

The shock can also cause the heart to stop completely (cardiac arrest) and this will lead to the cessation of breathing. Current passing through the respiratory center of the brain may cause respiratory arrest that does not quickly respond to the breaking of the electrical contact. These effects on the heart and respiratory system can be caused by currents as low as 25 mA. It is not possible to be precise on the threshold current because it is dependent on the environmental conditions at the time, as well as the age, sex, body weight and health of the person.

Burns of the skin occurs at the point of electrical contact due to the high resistance of the skin. These burns may be deep, slow to heal and often leave permanent scars. Burns may also occur inside the body along the path of the electric current, causing damage to muscle tissue and blood cells.

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Treatment Of Electric Shock And Burns

There are many excellent posters available which illustrate a first-aid procedure for treating electric shock and such posters should be positioned close to electrical junction boxes or isolation switches.

The recommended procedure for treating an unconscious person who has received a low-voltage electric shock is as follows:

  1. On finding a person suffering from electric shock, raise the alarm by calling for help from colleagues (including a trained first aider).
  2. Switch off the power if it is possible and/or the position of the emergency isolation switch is known.
  3. Call for an ambulance.
  4. If it is not possible to switch off the power, then push or pull the person away from the conductor using an object made from a good insulator, such as a wooden chair or broom. Remember to stand on the dry insulating material, for example, a wooden pallet, rubber mat or wooden box. If these precautions are not taken, then the rescuer will also be electrocuted.
  5. If the person is breathing, place him/her in the recovery position so that an open airway is maintained and the mouth can drain if necessary.
  6. If the person is not breathing, apply mouth-to-mouth resuscitation and, in the absence of a pulse, chest compressions. When the person is breathing normally place them in the recovery position.
  7. Treat any burns by placing a sterile dressing over the burn and secure with a bandage. Any loose skin or blisters should not be touched nor any lotions or ointments applied to the burn wound.
  8. If the person regains consciousness, treat for normal shock.
  9. Remain with the person until they are taken to a hospital or local surgery.

It is important to note that electrocution by high voltage electricity is normally instantly fatal. On discovering a person who has been electrocuted by high-voltage electricity, the police and electricity supply company should be informed.

If the person remains in contact with or within 18 m of the supply, then he/she should not be approached to within 18 m by others until the supply has been switched off and clearance has been given by the emergency services. High-voltage electricity can ‘ arc ’ over distances less than 18 m, thus electrocuting the would-be rescuer.

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Electrical Fires and Explosions

Over 25% of all fires have a cause linked to a malfunction of either a piece of electrical equipment or wiring or both. Electrical fires are often caused by a lack of reasonable care in the maintenance and use of electrical installations and equipment. The electricity that provides heat and light and drives electric motors is capable of igniting insulating or other combustible material if the equipment is misused, is not adequate to carry the electrical load or is not properly installed and maintained.

The most common causes of fire in electrical installations are short circuits, overheating of cables and equipment, the ignition of flammable gases and vapors and the ignition of combustible substances by static electrical discharges

Short circuits happen, as mentioned earlier if insulation becomes faulty, and an unintended flow of current between two conductors or between one conductor and earth occurs. The amount of the current depends, among other things, upon the voltage, the condition of the insulating material and the distance between the conductors.

At first, the current flow will be low, but as the fault develops the current will increase and the area surrounding the fault will heat up. In time, if the fault persists, a total breakdown of insulation will result and excessive current will flow through the fault. If the fuse fails to operate or is in excess of the recommended fuse rating, overheating will occur and a fire will result. A fire can also be caused if combustible material is in close proximity to the heated wire or hot sparks are ejected.

Short circuits are most likely to occur where electrical equipment or cables are susceptible to damage by water leaks or mechanical damage. Twisted or bent cables can also cause breakdowns in insulation materials. Inspection covers and cable boxes are particular problem areas. Effective steps should be taken to prevent the entry of moisture as this will reduce or eliminate the risk. Covers can themselves be a problem especially in dusty areas where the dust can accumulate on flat insulating surfaces resulting in tracking between conductors at different voltages and a subsequent insulation failure.

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The interior of inspection panels should be kept clean and dust-free by using a suitable vacuum cleaner. Overheating of cables and equipment will occur if they become overloaded. Electrical equipment and circuits are normally rated to carry a given safe current which will keep the temperature rise of the conductors in the circuit or appliance within permissible limits and avoid the possibility of fire. These safe currents define the maximum size of the fuse (the fuse rating) required for the appliance.

A common cause of circuit overloading is the use of equipment and cables which are too small for the imposed electrical load. This is often caused by the addition of more and more equipment to the circuit, thus taking it beyond its original design specification. In offices, the overuse of multi-socket unfused outlet adaptors can create overload problems (sometimes known as the Christmas tree effect).

The more modern multiplugs are much safer as they lead to one fused plug and cannot be easily overloaded. Another cause of overloading is mechanical breakdown or wear of an electric motor and the driven machinery. Motors must be maintained in good condition with particular attention paid to bearing surfaces. Fuses do not always provide total protection against the overloading of motors and, in some cases, severe heating may occur without the fuses being activated. Loose cable connections are one of the most common causes of overheating and may be readily detected (as well as overloaded cables) by a thermal imaging survey (a technique which indicates the presence of hot spots).

The bunching of cables together can also cause excessive heat to be developed within the inner cable leading to a fire risk. This can happen with cable extension reels, which have only been partially unwound, used for high-energy appliances like an electric heater. Ventilation is necessary to maintain safe temperatures in most electrical equipment and overheating is liable to occur if ventilation is in any way obstructed or reduced.

All electrical equipment must be kept free of any obstructions that restrict the free supply of air to the equipment and, in particular, to the ventilation apertures. Most electrical equipment either sparks in normal operation or is liable to spark under fault conditions. Some electrical appliances such as electric heaters are specifically designed to produce high temperatures. These circumstances create fire and explosion hazards, which demand very careful assessment in locations where processes capable of producing flammable concentrations of gas or vapor are used, or where flammable liquids are stored. It is likely that many fires are caused by static electrical discharges.

Static electricity can, in general, be eliminated by the careful design and selection of materials used in equipment and plant, and the materials used in products being manufactured. When it is impractical to avoid the generation of static electricity, a means of control must be devised. Where flammable materials are present, especially if they are gases or dust, then there is a great danger of fire and explosion, even if there is only a small discharge of static electricity.

The control and prevention of static electricity is considered in more detail later. The use of electrical equipment in potentially flammable atmospheres should be avoided as far as possible. However, there will be many cases where electrical equipment must be used and, in these cases, the standards for the construction of the equipment should comply with the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations, known as ATEX.

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Details on the classification or zoning of areas are contained in the Dangerous Substances and Explosive Atmospheres Regulations and ACOPs. Before electrical equipment is installed in any location where flammable vapors or gases may be present, the area must be zoned in accordance with the Dangerous Substances and Explosive Atmosphere Regulations, and records of the zoned areas must be marked on building drawings and revised when any zoned area is changed.

The installation and maintenance of electrical equipment in potentially flammable atmospheres is a specialized task. It must only be undertaken by electricians or instrument mechanics who are trained to ATEX standards. In the case of a fire involving electrical equipment, the first action must be the isolation of the power supply so that the circuit is no longer live. This is achieved by switching off the power supply at the mains isolation switch or at another appropriate point in the system.

Where it is not possible to switch off the current, the fire must be attacked in a way which will not cause additional danger. The use of a non-conducting extinguishing medium, such as carbon dioxide or powder, is necessary. After extinguishing such a fire, the careful watch should be kept for renewed outbreaks until the fault has been rectified. Re-ignition is a particular problem when carbon dioxide extinguishers are used, although less equipment may be damaged than is the case when the powder is used. Finally, the chances of electrical fires occurring are considerably reduced if the original installation was undertaken by competent electricians working to recognized standards, such as the Institution of Electrical Engineers ’ Code of Practice. It is also important to have a system of regular testing and inspection in place so that any remedial maintenance can take place.

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Electric Arcing

A person who is standing on earth too close to a high voltage conductor may suffer flash burns as a result of arc formation. Such burns may be extensive and lower the resistance of the skin so that electric shock may add to the ill effects. Electric arc faults can cause temporary blindness by burning the retina of the eye and this may lead to additional secondary hazards.

The quantity of electrical energy is as important as the size of the voltage since the voltage will determine the distance over which the arc will travel. The risk of arcing can be reduced by the insulation of live conductors. Strong electromagnetic fields induce surface charges on people. If these charges accumulate, skin sensation is affected and spark discharges to earth may cause localized pain or bruise. Whether prolonged exposure to strong fields has any other significant effects on health has not been proved. However, the action of an implanted cardiac pacemaker may be disturbed by the close proximity of its wearer to a powerful electromagnetic field.

Static Electricity

Static electricity is produced by the build-up of electrons on weak electrical conductors or insulating materials. These materials may be gaseous, liquid or solid and may include flammable liquids, powders, plastic films, and granules. Plastics have a high resistance that enables them to retain static charges for long periods of time. The generation of static may be caused by the rapid separation of highly insulating materials by friction or by transfer from one highly charged material to another in an electric field by induction.

A static electric shock, perhaps caused by closing a door with a metallic handle, can produce a voltage greater than 10 000 V. Since the current flows for a very short period of time, there is seldom any serious harm to an individual. However, discharges of static electricity may be sufficient to cause serious electric shock and are always a potential source of ignition when flammable liquid, dust or powders are present.

This is a particular problem in the parts of the printing industry where solvent-based inks are used on high-speed web presses. Flour dust in a mill has also been ignited by static electricity. Static electricity may build upon both materials and people. When a charged person approaches flammable gases or vapors and a spark ignites the substance, the resulting explosion or fire often causes serious injury.

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In these situations, effective static control systems must be used. Lightning strikes are a natural form of static electricity and result in large amounts of electrical energy being dissipated in a short time in a limited space with a varying degree of damage. The current produced in the vast majority of strikes exceeds 3000 A over a short period of time. Before a strike, the electrical potential between the cloud and earth might be about 100 million volts and the energy released at its peak might be about 100 million watts per meter of the strike.

The need to provide lightning protection depends on a number of factors, which include:

  • the risk of a strike occurring; the number of people likely to be affected;
  • the location of the structure and the nearness of other tall structures in the vicinity;
  • the type of construction, including the materials, used;
  • the contents of the structure or building (including any flammable substances);
  • the value of the building and its contents.

Expert advice will be required from a specialist company in lightning protection, especially when flammable substances are involved. Lightning strikes can also cause complete destruction and/or significant disruption of electronic equipment.

Portable Electrical Equipment

Portable and transportable electrical equipment is defined by the Health and Safety Executive as ‘ not part of a fixed installation but may be connected to a fixed installation by means of a flexible cable and either a socket and plug or a spur box or similar means’. It may be handheld or hand-operated while connected to the supply or is intended or likely to be moved while connected to the supply.

The auxiliary equipment, such as extension leads, plugs, and sockets, used with portable tools, is also classified as portable equipment. The term ‘ portable ’ means both portable and transportable. Almost 25% of all reportable electrical accidents involve portable electrical equipment (known as portable appliances). While most of these accidents were caused by electric shock, over 2000 fires each year are started by faulty cables used by portable appliances, caused by a lack of effective maintenance.

Portable electrical tools often present a high risk of injury, which is frequently caused by the conditions under which they are used. These conditions include the use of defective or unsuitable equipment and, indeed, the misuse of equipment. There must be a system to record the inspection, maintenance, and repair of these tools. Where plugs and sockets are used for portable tools, sufficient sockets must be provided for all the equipment and adaptors should not be used.

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Many accidents are caused by faulty flexible cables, extension leads, plugs, and sockets, particularly when these items become damp or worn. Accidents often occur when contact is made with some part of the tool which has become live (probably at mains voltage), while the user is standing on, or in contact with, an earthed conducting surface.

If the electricity supply is at more than 50 Vac, then the electric shock that a person may receive from such defective equipment is potentially lethal. In adverse environmental conditions, such as humid or damp atmospheres, even lower voltages can be dangerous. Portable electrical equipment should not be used in flammable atmospheres if it can be avoided and it must also comply with any standard relevant to the particular environment.

Air-operated equipment should also be used as an alternative whenever it is practicable. Some portable equipment requires substantial power to operate and may require voltages higher than those usually used for portable tools so that the current is kept down to reasonable levels. In these cases, power leads to a separate earth conductor and earth screen must be used.

Earth leakage relays and earth monitoring equipment must also be used, together with substantial plugs and sockets designed for this type of system. Electrical equipment is safe when properly selected, used and maintained. It is important, however, that the environmental conditions are always carefully considered. The hazards associated with portable appliances increase with the frequency of use and the harshness of the environment (construction sites are often particularly hazardous in this respect). These factors must be considered when inspection, testing, and maintenance procedures are being developed.

Secondary Hazards

It is important to note that there are other hazards associated with portable electrical appliances, such as abrasion and impact, noise and vibration. Trailing leads used for portable equipment and raised socket points offer serious trip hazards and both should be used with great care near pedestrian walkways.

Power drives from electric motors should always be guarded against entanglement hazards. Secondary hazards are those additional hazards which present themselves as a result of an electrical hazard. It is very important that these hazards are considered during a risk assessment.

An electric shock could lead to a fall from a height if the shock occurred on a scaffold or it could lead to a collision with a vehicle if the victim collapsed on to a roadway. Similarly, an electrical fire could lead to all the associated fire hazards outlined in Chapter 13 (e.g. suffocation, burns and structural collapse) and electrical burns can easily lead to infections.

1 COMMENT

  1. Electrical safety should be considered as an important concept. Lots of people die each year due to electrical injuries at workplace or home. hudsonelectricalnb.com.au

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