Direct contact electric shock

The majority of direct and indirect contact electric shock and burn accidents occur at 230 V on distribution systems or on connected equipment. There are many instances in which high voltage overhead lines are touched, so this is a form of direct contact however, they usually result in predominantly burn injuries rather than electric shock. 

Protective measures against direct and indirect contact (electric shock) are required depending on the battery nominal voltage and the chosen ground system of the electric network (Table 6.4). In the case of a system short circuit an effective protection can be achieved by incorporating a system with protective conductor and associated protective devices. In battery installations mainly an IT network or TN network is used. 

Primary explosives are a group of substances which are highly sensitive to the action of mechanical shock and are readily ignited by direct contact with flame or electric sparks. 

This conclusion, though incorrect, is quite understandable because at that time the attention of scientists had been directed to the peculiar electric shocks given by certain eels. In 1793, however, Volta, professor of natural philosophy at Pavia, dissented from this view in a paper presented to the Royal Society and suggested that the observed agitation was caused by an electric discharge due to contact of the two dissimilar metals, copper and... 

Two types of contact will result in a person receiving an electric shock. Direct contact with live parts involves touching a terminal or line conductor that is actually live. The regulations call this basic protection, indirect contact results from contact with an exposed conductive part such as the metal structure of a piece of equipment that has become iive as a resuit of a fauit. The regulations call this fault protection. 

Electrical burns occur from environmental, domestic and industrial sources. Of 290 fatal factory accidents in Great Britain, 21 were due to electric shock a larger number died from burns after contact with domestic 240-V alternating current (50 Hz) (Cason 1981). The lesions are due to heat and direct injury by electricity, the severity depending, for example, on current voltage, thickness and wetness of the skin, and... 

The electricity supply company has one of its conductors solidly connected to the earth and every circuit supplied by the company must have one of its conductors connected to earth. This means that if there is a fault, such as a break in the circuit, the current, known as the earth fault current, will return directly to earth, which forms the circuit of least resistance, thus maintaining the supply circuit. This process is known as earthing. Other devices, such as fuses and residual currertt devices, which will be described later, will also be needed within the circuit to interrupt the current flow to earth so as to protect people from electric shock and equipment from overheating. Good and effective earthing is absolutely essential and must be connected and checked by a competent person. Where a direct contact with earth is not possible, for example, in a motor car, a common voltage reference point is used, such as the vehicle chassis. 

OSHA has requirements for safe work practices at 1910.333. By not complying with these work practices employees performing work near or on equipment or circuits (which are or may be energized) could be exposed to electric shock or other injuries resrdting from either direct, or indirect, electrical contacts. Your company-specific safety-related work practices must be consistent with the nature and extent of the electrical hazards. 

If, for any reason, there was a breakdown of insulation in a part of an electric circuit or in any apparatus such as, say, a hand-held metal-cased electric drill, it is conceivable that current would flow external to this supply circuit, if a path were available. For example, the metalwork of the drill may be in contact with a live internal conductor at the point of insulation breakdown. Or, take the example of someone working at a switch or socket outlet from which the cover had been removed before the electricity supply had been isolated. In both circumstances the person concern could come into contact with a live part, either metalwork of the drill made live because of the internal fault condition or a live terminal exposed by removal of the cover which, if the conditions were right, would allow an electrical current to flow through the body to earth. The former is an example of electrical shock received by indirect contact whilst the latter is an example of electrical shock from direct contact. If the total resistance of the earth fault path were of a sufficiently low value, the current could kill or maim. 

Accidents involving an electric shock are usually subdivided into two categories - direct contact and indirect contact shocks. The standards that will be considered later use this distinction. A direct contact shock occurs when conductors that are meant to be live, such as bare wires or terminals, are touched. An indirect contact shock is usually associated with touching an exposed conductive part that has become live under fault conditions an example of an exposed conductive part would be the metal casing of a washing machine. 

The majority of fixed apparatus is of Class I construction, as defined in BS 2754 1999 Construction of electrical equipment for protection against electric shock. This means that it usually has a metal case enclosing the live parts and that the five parts are insulated from each other and from the carcass by basic insulation only. The case, which is earthed by connection to the protective conductor, protects the internal wiring and components from damage and prevents direct contact. 

Circuit breakers and fuses are installed in circuits to operate in the event of excess current arising from overload conditions and faults. The most common type of fault is an earth fault, but it is frequently the case that the current flowing due to earth faults is too low to operate the overcurrent protection devices. In addition, the overcurrent protective devices will not operate in the event of somebody making direct contact with a live conductor the current which flows through the body to earth will be too low to operate the devices but will often be high enough to cause fatal electric shocks. These two problems can be obviated by the use of earth leakage protection devices. 

The intention of Regulation 7 is to prevent electric shock and burn injuries from direct and indirect contact, and fire and explosion consequent on short circuits or leakage currents between circuit conductors or between circuit and other conductors. 

Electrode holders should be insulated to prevent contact with live parts as far as possible. There are two types of electrode holder specified in BS EN 60974-11 1996 - Types A and B. Type A is less versatile than type B but somewhat safer as no live parts are accessible to the standard test finger and when the electrode is fitted, its non-coated end does not protrude from the electrode holder head. To avoid direct electric shocks, operators should not change electrodes with bare hands unless the power source is switched off A box made of incombustible insulating material should be provided for the operator to rest the electrode holder when not in use to avoid the possibility of extraneous metal being made live by contact with a live electrode stub and/or causing stray currents. When the task is completed and/or the operator is not present, the power source should always be switched off. 

Typically the actual number of potentially dangerous electrical contacts is higher than the injury data implies. One laboratory performed a questionnaire study of electrieal safety practices with interview follow-up. The 3000 person population studied had a direct exposure to a broad spectrum of electrical hazards. The response data from the questionnaire represented a signifieant pereentage of the population. A simple reduction of the response data indicated that four painful electrical shocks occurred daily in that population. Only a handful of shocks actually were reported each year. 

Contact. Direct-contact injury can be caused by sharp or abrasive surfaces, or by energies (electrically live components can cause shock and hot surfaces can burn). This category includes contact with fast-moving saws and abrasive wheels. 

Electrical protective devices are used to protect machines and equipment from damage due to values of voltage or current exceeding design levels. They are also used to protect individuals from the risk of injury, by isolating electrical faults in part of the system. Electrical hazards associated with workshop machinery and tools may be caused by overload current, short-circuit current, or electric shocks to individuals arising from direct or indirect contact with live conductors. Overload current is an excessive current... 

Electric shock sustained from direct contact. 

Elecric shock as a result of direct contact, means that a person makes contact with part of the circuit which is intended to be live. The only form of protection against direct contact is to prevent such contact in the first place. This can be achieved by following the same principles of risk assessment and machinery safeguarding discussed earlier, namely to provide fixed guards, enclosures or insulation. However, if access is foreseeable, then permit-to-work systems should be operated. It should be remembered that intrinsic safety is an absolute priority in removing the risk of shock injury. This can be achieved by reducing the system voltage in areas of likely contact to such an extent that it cannot result in an electric shock. 

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