Shock enhanced risk

Chapter 1, bathrooms and showers, contains a helpful explanation of why there is an increased shock risk in wet locations and what needs to be done to protect people against those enhanced risks. 

Although propofol is generally said to be a remarkably safe dmg, 14 patients were reported to have life-threatening reactions within a few minutes of the administration of propofol, numerous other anaphylactic-like reactions have been reported, and other occasionally observed hypersensitivity reactions include bronchospasm, angioedema, urticaria, and erythematous rash. The overall incidence of anaphylaxis induced by propofol in France is about 1 % and 0.65 % in the Australian survey (Table 7.1). Another survey estimated that 1.2 % of cases of perioperative anaphylactic shock were attributable to propofol. Risk factors for a reaction are said to be a history of previous dmg allergy and the use with atracu-rium, the latter because of possibly enhanced histamine release. 

The intention of SELV is to minimise the shock hazard by voltage limitation. Subsection 411-02 sets out the parameters, which include a safe source of supply such as a safety transformer to BS 3535 and other precautions to avoid the SELV circuit becoming live at a higher voltage. If the SELV does not exceed 25 V a.c. or 60 V ripple-free d.c., i.e. not more than 10% ripple, the direct contact shock risk is regarded as negligible and exposed live parts are allowed except in locations of enhanced shock risk, such as most of those in Part 6 where the conductors have to be protected against direct contact by a barrier, enclosure or insulation. The SELV circuit is not earthed and the cables are not metal-sheathed. As conductive parts of the installation are not deliberately or fortuitously earthed, it will usually be more practicable to use insulated rather than metallic conduit and ducts. 

Regulation 471-08-03 refers to locations where the installation supplies fixed equipment outside the equipotential zone, e.g. an outside motor-driven pump for a garden fountain, and the equipment has exposed conductive parts. In such cases. Table 41A applies and the maximum interruption time is 0.4 s for 230 V equipment. 230 V outdoor portable apparatus, such as an electric hedge trimmer, requires sensitive RCD protection see Regulation 471-16-01. There are similar protection requirements for circuits in locations of enhanced shock risk such as those in Part 6 see Regulation 471-08-01. 

Supplementary bonding must be provided in bathrooms even if there are satisfactory metal-to-metal joints because of the enhanced shock risk see section 601. Consideration should be given to the provision of supplementary equipotential bonding in kitchens, sculleries and laundry rooms with conducting floors, such as quarry tiles, particularly if they are likely to be wet, again because of the enhanced shock risk. Similar locations in commercial and industrial premises should receive the same consideration. 

The enhanced shock risk in swimming pools is similar to bath and shower locations so similar precautions are specified. There are three zones - A, B and C in descending order of risk. Zone A is in the pool, chute or flume zone B is from the poolside up to 2.5 m vertically and 2 m horizontally from the rim of the pool, and zone C is the 1.5 m zone surrounding zone B. 

The more usual description for section 606 is confined conductive locations. These are spaces where freedom of movement is restricted and the body is likely to be in contact with exposed and extraneous conductive parts. This section covers work inside boilers, metal ventilation ducts and tanks, for example, where extensive contact with the metalwork increases the indirect shock hazard. The risk is enhanced if these interiors are wet or so hot that the operator s clothes are soaked with perspiration. Incidentally, although not... 

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... 

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