Electrical safety shock hazards

Hazards. Eyes and skin can be severely injured by ultraviolet radiation. One should avoid looking at the reaction mixture when the irradiation source is activated. The photochemical apparatus, especially when using immersion set-ups, must be wrapped appropriately to avoid exposure to the ultraviolet radiation. In view of the high temperatures produced by the lamp, efficient cooling is mandatory. Special care must be exercised when flammable solvents are used. Ozone is also produced, so that working in an efficient hood is essential. Furthermore, proper electrical safety is necessary to avoid high voltage shocks. 

Electric DisposaL A disposer can be installed in any sink that has a full-size drain opening. For an assistive kitchen design, switch location, safety, and disposal location are the main design objectives. The on and off switch should be placed in an accessible area, possibly under the front lip of the countertop. Care should be taken not to position the switch where a wheelchair can accidentally bump the switch while the person is washing the dishes. It should also be located so that a person cannot contact the sink and switch at the same time. The electrical connection should be away from the water line and should be protected with a conduit pipe to eliminate any shock hazard. The disposal should be located away from any wheelchair-accessible area. 

Electrical safety on offshore wind turbines and substations Working with high-voltage systems that expose personnel to electrical energy involves such hazards as electrical shocks, electrical burns, arc flashes (burns and blasts), and electrocution. 

Voltage and Shock Hazards. Inside the cell room, it is a practical necessity for operators to come into contact with live parts. Since some of the usual safety measures against electrical hazards do not apply, special codes of practice have been formulated. 

As outlined previously in this chapter, the primary purpose of grounding electronic hardware is to prevent electric shock hazard. The National Electrical Code (NEC) and local building codes are designed to provide for the safety of the workplace. Local codes should always be followed. Occasionally, code sections are open to some interpretation. When in doubt, consult a field inspector. Codes constantly are being changed or... 

OSHA considers 50 volts to be the recognized threshold for hazardous electric shock. Several OSHA and national consensus standards recognize this 50-volt threshold. OSHA s general industry and construction electrical standards both require guarding of live parts energized at 50 or more volts. Also, the NFPA70E and the National Electrical Safety Code have electrical safety requirements starting at 50 volts. 

Section 9 deals with the electric shock hazard when the supply is PME and there is a potential difference between the PME terminal and the Class I metalwork bonded to it and true earth, and the precautions needed to ensure safety. It fails, however, to mention the worst case (admittedly rare) which arises from a break in the PEN conductor. 

In confined and conductive locations the potential electric shock hazard is increased and special precautions are needed. Examples of confined, conductive spaces are inside boilers and other metal vessels or inside metal pipes, flues and ducts where the area of body contact to earthed metalwork is likely to be substantial. Even if the interior is dry, the shock risk is enhanced, but if it is damp it is worse. In these circumstances the llOV system is not considered safe and pneumatic, hydraulic or battery powered tools are advocated. For lighting, battery powered cap and hand lamps could be used or the luminaires could be supplied from a safety transformer at not more... 

As mentioned previously, ISO 26262 defines functional safety as freedom of unacceptable risks based on hazards, which are caused by malfunctional behavior of E/E-systems. However, interactions of systems with E/E-functions are included as well and therefore also mechatronic systems. Whether pure mechanical systems really show not any interactions with E/E is doubtful. Furthermore, the introduction chapter of ISO 26262, which describes the scope of the norm, excludes hazards such as electric shock, fire, smoke, heat, radiation, poisoning, inflammation, (chemical) reactions, corrosion, release of energy or comparable hazards, as long as the failure was not caused by electrical components. Such hazards are caused more by the battery as well as the poisonous electrolytes in the capacitors. Whether a motor winding is an electrical device or a mechanical component is also questionable. 

Several companies now sell equipment based on some or all of the principles outlined in the letter. However, there is no published U.S. standard for such equipment Hence, they can only be listed for electrical safety — fire and shock hazards — not for their safety function. 

Electrical safety begins with understanding the hazards such as electrical shock and electrical arc flash. If skin comes in contact with electricity, it may be fatal. In an electrical arc flash, temperatures can reach 35,000°F, which is four times hotter than the surface of the sun. Fatal bums can occur at a distance as far as 10 feet. 

The first priority in electrical work is locking out and tagging the equipment rendering it electrically safe. If that is not possible, then employers must ensure employees are protected against electrical hazards through safe work practices and appropriate PPE. The OSHA regulations do provide shock protection methods in 1910.137— Electrical protective devices. However, the OSHA rules do no provide for arc flash/blast protection. Tb protect employees from those hazards, employers must refer to an outside sormce such as the National Fire Protection Association s NFPA TOE—Standard for Electrical Safety in the Workplace. 

Safety interlocks, common to machinery, provide a means either of preventing operator access to a hazardous area until the hazard is removed or of automatically removing the hazardous condition (i.e., electric shock, moving parts) when access is gained. Safety interlocks have special requirements, such as fail-safe design, positive opening, and nonoverridable type. 

Street shoes may not be appropriate in the laboratory, where both chemical and mechanical hazards may exist. Substantial shoes should be worn in areas where hazardous chemicals are in use or mechanical work is being done. Clogs, perforated shoes, sandals, and cloth shoes do not provide protection against spilled chemicals. In many cases, safety shoes are advisable. Shoe covers may be required for work with especially hazardous materials. Shoes with conductive soles are useful to prevent buildup of static charge, and insulated soles can protect against electrical shock. 

A quarter of all serious electrical accidents involve portable electrical appliances that is, equipment which has a cable lead and plug and which is normally moved around or can easily be moved from place to place. This includes, for example, floor cleaners, kettles, heaters, portable power tools, fans, televisions, desk lamps, photocopiers, fax machines and desktop computers. There is a requirement under the Health and Safety at Work Act for employers to take adequate steps to protect users of portable appliances from the hazards of electric shock and fire. The responsibility for safety applies equally to small as well as large companies. The Electricity at Work Regulations 1989 also place a duty of care upon employers to ensure that the risks associated with the use of electrical equipment are controlled. 

Key hazards of electric-powered tools include burns and slight shocks that can lead to injuries or heart failure. To protect users from shock, tools must contain a three-wire cord with a proper ground. Tools can also contain double insulation or powered by a low-voltage isolation transformer. Operate electric tools within their design limitations. Recommend use of gloves and safety footwear when using electric tools. Never use electric tools in damp or wet locations. Keep work areas well lighted. 

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