Electrical Hazards – Descriptions & Effects
Thursday, August 23rd, 2007
The following effects can be caused by a faulty electrical appliance, thorough PAT (Portable Appliance) Testing can negate these effects. However there can be no replacement for a thorough understanding of the effects by the user themself. The user is the first line of defence against injury.
Personal Injury
(i) Electric Shock
Electric shock is the effect produced on the body, particularly its nervous system, by an electrical current passing through it. The extent of injury depends upon the current strength which in turn depends upon the voltage, the path the current takes through the body, the surface resistance of the skin (much reduced when wet) and several other factors. A voltage as low as 15V can produce discernible shock effects and 70 V has been known to cause death. But, generally speaking, fatalities involve domestic voltages (240Vac) or higher and currents of 25-30 milliamps. The most common cause of death from shock is suffocation and accordingly it is highly desirable that those dealing with electricity should be trained in resuscitation. Minor shocks in themselves may not be serious but they can lead to serious consequences; for example, the associated muscle contraction may lead to falls from working platforms or ladders.
(ii) Burns
These are caused by the passage of heavy current through the body or by direct contact with an electrically heated surface. They may also be caused by the intense heat generated by arcing from a short circuit. Electrical burns are a very unpleasant form of burn and require immediate medical attention.
Explosions
The main causes of electrically induced explosions are:-
(i) In situations where flammable gases or vapours are present so that a spark could initiate an event. In such environments all electrical equipment should be flame-proofed.
(ii) Where electrical arcing takes place in a confined space causing intense local heating with consequent bursting of the enclosure by the expansion of trapped air.
Fires
A large percentage of fires are of electrical origin, caused by one or more of the following:-
(i)
A spark arises from a sudden discharge through the air between two conductors, or from one conductor to earth. The current produced is usually small so that serious fires are unlikely unless explosive gases or vapours are present, or highly flammable material is in contact with the conductor.
(ii) Arcs
An arc is a much larger and brighter discharge where the current flow may be hundreds of amps. It usually arises when a circuit is broken or when a conductor melts or fractures leaving a gap across which the current continues to flow. When an arc is struck, the air in the vicinity becomes ionised and forms a conductor which may allow current to flow to a nearby metal framework. Any combustible material in the vicinity could therefore lead to a fire.
(iii) Short circuits
A short circuit is formed when the current finds a path from the outward conductor wire to the return wire other than through the equipment to which it is connected. The current flow may be large because of the low resistance of the leads and arcing often occurs at a contact between the conductors. Insulation may therefore be burned and set fire to adjacent flammable material.
January 28th, 2009 at 3:37 am
Good work! Thank you very much!
I always wanted to write in my site something like that.
Sincerely, Timur I.