No discussion of electrical safety would be complete without mentioning electrical shock.

Generally speaking, an electric shock is the effect produced on a person’s body by an electric current passing through it. The situation arises when the body acts as a link between points in an electric circuit of different potential. This might happen when a live conductor is touched by hand (or some live object is touched) and current escapes through the body to earth. It is also likely to happen when the body comes between two live conductors (say of two different phases). In all cases of electric shock, consideration must be given to three interrelated factors, namely: voltage, size of current and duration time. It is difficult to specify the exact voltage which is likely to prove fatal but values below 100 volts have been known.

The size of current is a function of voltage and body resistance. A person’s body resistance varies with the applied voltage: for example, at 230 volts, the resistance when the skin is damp is around 1100 ohms. Using Ohm’s Law

1 =	V	(	current in amps =             Volts	)
	R		Resistance in ohms

1 =	230	= 0.209A or 209 milliamps
	1100

A current which is just over one-fifth of 1 amp will flow.

Research has shown that a current passing through the body approaching 15 milliamperes, while not actually critical, is sufficient to be very painful. The physical signs are involuntary muscle contractions making it difficult to release one’s grip - the person becomes ‘frozen’ to the fault. A current of about 34 milliamperes may cause chest muscles to contract, which can restrict breathing and result in asphyxiation. At a level around 50 milliamperes, severe pain is experienced, the body becomes paralysed and there is loss of consciousness. Beyond 50 milliamperes, the body is paralysed, resulting in loss of pulse and respiration; death eventually occurs due to ventricular fibrillation (a disturbance which causes no blood to be pumped to the heart).

The third factor mentioned, the duration, is the length of time for which the current flows. Research has shown that if this is no more than about 30 milliseconds, ventricular fibrillation is unlikely.

Only a small current is required to bring about an electric shock, but a person’s body resistance is a variable which has to be taken into consideration: for example, thick horny skin has a high resistance, whereas moist skin has a low resistance. Another factor here is the type of protection we provide for our bodies, the type of clothes and footwear: these can greatly reduce the risk of electric shock.

This is the reason why SELV units are recommended in bath and shower rooms where the fan is within reach of a person in a bath or shower basin.

The IEE Wiring Regulations 16th Edition (BS7671, 1992) classify bath/shower rooms as "special locations giving rise to increased risk of electric shock".

For safety, whenever an electrical appliance is used, especially outside the house, it should have theprotection of an RCCB. If the consumer unit is not fitted with RCCB’s, a plug in version can be used. This goes into the socket and the appliance plugs into the device.