Electrical safety precautions

The non-electrical safety precautions comprise protective clothing for the operator to prevent burn injuries from arc sputter and the ultraviolet and infrared radiation produced by the arc. A visor is used to protect the face, with an aperture fitted with a filter glass through which the operator observes the area. It is usually necessary to provide extract ventilation to remove fumes, and opaque or filter screens, arranged around the operator, to protect other people in the vicinity from ultraviolet radiation (see Fig. 16.2). 

From an historical perspective, in order to avoid indirect contact electric shock, the now-superseded 1966 edition of BS 638 Specification for arc welding plant, equipment and accessories, recommended that the power source metalwork and the work piece should be earthed. This was a safeguard against an interwinding fault in a transformer source causing the 

Before adopting the practice of not earthing the work piece, a user of a power source which predates BS 638 Parts 9 or 10 1990 should determine, preferably by asking the manufacturer or supplier, whether or not the transformer is as safe as a BS 3535 transformer. Some of the existing older transformers and transformer rectifiers will not comply, and in these cases either the welding transformer should be replaced with one that does meet the more modern specification, or the practice of earthing the work piece should be continued. 

Welding circuits supplied from engine-driven generators do not need not to be earthed as there is no risk from mains voltage. 

Where a single power source is used to supply a number of welding circuits, as shown in Fig. 16.4, distribution boxes and regulators are employed to provide a regulated supply for each operator. This equipment is usually of heavy Class I construction and the metalwork is earthed to avoid indirect electric shocks. 

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An explosion and fire (March 13, 1991) occurred at an ethylene oxide unit at Union Carbide Chemicals Plastics Co. s Seadrift plant in Port Lavaca, TX, 125 miles southwest of Houston. The blast killed one, injured 19, and idled the facility, that also produces ethylene, ethylene glycol, glycol ether ethanolamines, and polyethylene. Twenty-five residents were evacuated for several hours as a safety precaution. The plant lost all electrical power, for a few days, because its cogeneration unit was damaged. The Seadrift plant, with 1,600 workers, is capable of making 820 million lb per year of ethylene oxide which is one-third of Carbide s worldwide production of antifreeze, polyester fibers, and surfactants Seadrift produces two thirds of Carbide s worldwide production of polyethylene. 

FPN No. 3) Certain dusts may require additional precautions due to chemical phenomena that can result in the generation of ignitable gases. See National Electrical Safety Co[Pg.639]

Hazard, i.e. the potential of the material to cause injury under certain conditions (flammability, explosion limits in air, ignition and autoignition temperatures, static electricity (explosions have occurred during drying due to static electricity), dust explosion, boiling point, fire protection (specification of extinguishers, compounds formed when firing), R S (nature of special risk and safety precautions). Table 5.2-5 lists hazards associated with typical chemical reactions. 

One must document any potential hazards and safety precautions, including any possible electrical/line interference. This may also include suggested safety checks. 

Normal safety precautions for laboratory work and for the use of electrical equipment, especially variable temperature accessories, must be observed. The thermal analysis experiment involves high temperatures and there is a danger of being burned. Consult instrument operating manual for specific cautions regarding operation. 

Some general precautions are avoidance of continuous exposure, practice of electrical safety and equipping entry doors to the laboratory with electronic interlocks in order to shut off the field-generating equipment upon entry. 

GENERAL SAFETY PRECAUTIONS WHEN WORKING WITH ELECTRICAL DEVICES... 

As a general safety precaution, tanks should be grounded to discharge any static electricity. 

Clarifications are also required by statutory authorities before granting consent to start operations (generally these pertain to safety precautions, pollution control equipments, electrical power required for initial constmction, and continuous running afterwards). 

Special safety precautions are taken for electromedical equipment. Both patient and operator safety is considered (as well as damage of property). Electromedical equipment is equipment situated in the patient environment and is in physical contact with the patient, or which can deliver energy (electrical, mechanical, or radiation) to the patient from a distance. Equipment for in vitro diagnosis is also important for patient safety with respect to correct diagnostic answers, but as long as it is not in the patient environment, the safety aspects are different. 

The risk associated with an experiment should be determined before the laboratory work begins. The hypothetical question that should be posed before an experiment is, "What would happen if... " For the possible contingencies, preparations should be made to take the appropriate emergency actions. The worka- should know the location of emergency equipment and how to use it. He or she should be familiar with emergency procedures and should know how to obtain help in an emergency. Any special safety precautions that may be required should be addressed before the experiment is begun. The consequences of loss of electrical power or water pressure should also be considered. 

Saliva contains a mixture of ionic substances and can conduct electricity. For this reason, there can be no direct electrical pathway from the ac supply to the patient. Thus use of isolation transformers should be seriously considered, especially when young children are to be measured. An alternative is the use of battery-powered units, which are especially attractive because there cannot be a stray path to ac electrical ground as long as the unit is not hooked to an electrical outlet. Although most hospitals have grounded ac outlets and ground fault interrupters, respiratory medical devices are being used in homes, clinics, and schools where such safety precautions may not be installed. 

If you can answer yes to the above points then the risks are adequately controlled, but you need to state the precautions you have put in place. You can refer to company procedures, company rules, company practices, etc. in giving this information. For example, if we consider there might be a risk of electric shock from using electrical power tools, then the risk of a shock will be less if the company policy is to portable appliance test (PAT) all power tools each year and to fit a label to the tool showing that it has been tested for electrical safety. 

The design of the instrumentation, control and electrical systems corresponds with the safety concept for safe reactor operation, and advanced electronic and information processing technology has been incorporated in the design. The plant is automated to a high degree, and all safety precautions are taken into account. The plant control scheme is based on "the reactor follows plant loads principle". 

Power tools can be hazardous when improperly used. There are several types of power tools, based on the power source they use electric, pneumatic, liquid fuel, hydraulic, and powder-actuated. Employees should be trained in the use of all tools (not just power tools). They should understand the potential hazards as well as the safety precautions to prevent hazards from occurring. The following general precautions should be observed by power tool users ... 

DC is little used in standard electricity distribution systems but is used in industry for special applications. Although there are slight differences in the effects under fault and shock conditions with dc when compared with ac, it is a safe rule to apply the same general safety precautions for the treatment of electric shock. 

However well an electrical installation or apparatus is designed and constructed, however well it is operated or worked upon, however adequate are the systems and methods of work and the protective clothing and safety equipment provided and used, safety precautions are incomplete unless suitable arrangements are made for proper maintenance and testing by competent people. 

Crane booms must not be allowed to move in the vicinity of live electrical conductors unless effective clearance is maintained, as required, and adequate safety precautions are taken for the voltage concerned. 

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