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There are various factors, which affect the injury to the person experiencing electric shock. These factors are as under:
1.0 Amplitude of current: When current passes from some route of the body, it will have effect on the muscles, heart etc. Injury depends on amplitude & time. When 50 Hz current passes from left hand to both legs & to the earth, for one second, it has different effects at different values, as tabulated below:
Table-1 Effect current
| Current (mA) | Effect |
| Up to 1 | No sensation |
| 1 to 8 | Painful shock, but muscular control still there. |
| 8 to 15 | Sensation there, but not painful |
| 15 to 20 | Muscular controls lost, resulting in sticking |
| 20 to 50 | Severe muscular contraction |
| 50 to 200 | Ventricular fibrillation and possible death |
| 200 & above | Severe burns, severe ventricular fibrillation resulting in death. |
2.0 Duration of current: Duration of current & amplitude, both are inter-related in deciding the injury. If current passes for longer time, body will absorb more energy. Injury will also be more. Relationship between Time & Current is shown in Fig.1
Fig.1 Effects of AC on human body
Table-2 Effect of current thro’ Human body
| Zone | Physiological effects |
| Zone-1 | Usually no reaction effects |
| Zone-2 | Usually no harmful physiological effects |
| Zone-3 | Usually no organic damage to be expected. Likelihood of muscular contractions and difficulty in breathing, reversible disturbances of formation & conduction of impulses in the heart, including atrial fibrillation & transient cardiac arrest without ventricular fibrillation increasing with current magnitude and time |
| Zone-4 | In addition to the effects of Zone-3, probability of ventricular fibrillation increasing up to @ 5% (curve c2), up to @ 50% (curve c3) and above 50 % beyond curve c3.Increasing with magnitude and time, pathophysiological effects such as cardiac arrest, breathing arrest and heavy burns may occur |
3.0 AC or DC: Injury caused by AC is more as compared to that caused by same value DC, because 50 Hz AC changes direction 100 times in one second. This is dangerous for heart. Duration of current & time are inter-related. Relationship between time & current for DC can be seen in Fig.3
Fig.3 Relationship between time & current for DC
1. Route of current – Left hand to feet to earth & for rising current (feet represent positive polarity.
2. Boundary between Zones 2 & 3 unknown for times less than 500 mS.
Above chart and data for AC & DC are taken from IS: 8437(Part-1):1993 and IEC 479-1 (1984) –Guide on effects of current passing through the human body
4.0 Condition of the body: Dry skin offers 100K to 600K ohm resistance to current. Wet skin
= voltage / resistance of body).
5.0 Sex & age of the person: Average resistance of female is 66% of that of male. Also, the average resistance of a child is still less. Therefore, women and children are more prone to danger of electrical shock. They should be very careful while using any electrical gadget.
6.0 Ambient temperature and humidity: When ambient temperature is higher, there will be lot of perspiration. If humidity is high, body will not get dried and wet body has very low resistance.
7.0 Oxygen & CO2 content in surrounding air: when O2 content is low and CO2 content is high in the air breathed in by a person, his body resistance drops down as compared to the values mentioned in 2.4.
8.0 Material / Flooring: If a person is standing on the Dry wooden floor or some type of insulated flooring (like rubber insulated mat), he is well protected. Wet floor offers less than 100-ohm resistance. Most of the electrical accidents in the bathrooms are fatal because of this reason. Insulated rubber mat is laid on the floor in front and read side of HT & LT panels. If electrician is working on the panel and he is protected, if no other part (like foot or leg) is touching the earth or earthed material or floor.
9.0 Position of hands and legs decides the path of current passing through the body to earth. The most dangerous condition is the one in which current passes through the heart. In2.8, if electrician is standing on the rubber insulated mat, but his other hand on the panel body (which is earthed), current will pass from one hand to heart and then to earth through other hand. This will cause very serious injury or even fatality.
10.0 Condition of earthing: If condition of earthing is good, protection system will immediately respond and disconnect the faulty equipment. But, if earthing is not proper, the system or person will not be protected.
