This chapter discusses the physiological effects of electric current and shock hazards.

This chapter discusses earthing and electrical apparatus protection.

With the wider use of natural gas and of petroleum accidental ignitions of accumulations of flammable gases and vapours are a major industrial hazard. The mode of combustion is usually explosive and often results in injury, death and widespread destruction. In today's complex society the only wholly safe procedure when gases and vapours are released to the atmosphere is to ensure that they are immediately ignited. This may sound anomalous but the safest way to vent a flammable gas is to burn it off at the point of release. A flare stack works on this principle. A processing furnace using an oxygen-free atmosphere and gas such as hydrogen for instance can be protected from dangerous release of gas by a so-called flame curtain consisting of small flame jets round the furnace portals.

In conclusion, it will be seen that protection by the method of intrinsic safety has grown rapidly due to its eminent suitability for very low voltage, low power process control and information transfer installations. It differs from other types of protection for electrical apparatus in potentially explosive atmospheres because the flow of energy from the safe area must be carefully controlled. Its growth has been greatly accelerated by the development of barrier devices which protect the hazardous area from the possible intrusion of dangerous sources of energy from the safe area parts of the system.

The failure or breakdown of electrical equipment can sometimes be blamed on faulty design or poor workmanship. Often, but not necessarily more often, it is the result of inadequate maintenance. This chapter discusses the effects of faulty design.

There are two ways in which electricity is used for welding; by an arc and by resistance. Both depend on heat generated by an electric current. The welder must always protect him or herself with suitable personal protective equipment PPE as a defence against some of the above hazards. This equipment should include safety boots, apron, gauntlets, head, face and eye protection. It is also very advisable to keep ones overalls buttoned at the neck.

Electrostatics is the study of electrical phenomena that take place when there are no moving charges. Static, the commonly used term for both charges and discharges, has many uses such as in printing and copying, dust precipitation, micro-electronics and in sprayed paint and powder coating. Electrostatic discharges (ESD) present many problems particularly with regard to ignition hazards, ranging from macro-scale disasters in grain silos and supertankers, to the explosion of the lungs of hospital patients while under anaesthetic. In addition, ESD costs the micro electronics industry untold millions.

As is well known, the direct current motor was invented many years before the alternating current induction motor. The d.c. motor goes back to the discovery by Faraday in 1821 of electromagnetic induction and rotation. His work was rapidly followed during the next few decades by a great variety of designs and patents for both motors and dynamos. Many of these incorporated novel and complex ideas. One of the early machines designed by Professors Elihu Thomson and Edwin J. Houston of Philadelphia included a brush-rocking device controlled by the load current. The commutator had only three segments and, to prevent damage to the surface, the sparks were blown out by synchronised blasts of air from an integral rotary vane pump as the gaps between the segments passed under the brushes.