Electricity hazards and control

Note A discussion of the pneumatic loading system and the hazards involved is presented in the DuPont Technical Bulletin, entitled "Static Electricity Hazards and Their Control in Pneumatic Loading Systems ... 

The laboratory shall be equipped with a fume hood. The fume hood should meet any specific safety requirements mandated by the nature of the research program. A discussion of hood design parameters will be found in a later section, but for high hazard use the interior of the hood and the exhaust duct should be chosen for maximum resistance to the reagents used the blower should either be explosion-proof or, as a minimum, have non-sparking fan blades the hood should be equipped with a velocity sensor and alarm should the face velocity fall below a safe limit the interior hghts should be explosion-proof, and all electrical outlets and controls should be external to the unit. It may be desirable to equip the unit with an internal automatic fire suppression system. 

You need to instill in your employees a healthy respect for electricity and its power. Safe work practices are essential. Training can ensure your employees recognize electrical hazards and use safe work practices to control or eliminate those hazards. 

Electricity and electrical equipment create or contribute to several hazards. The most common ones are electric shock, heat, fire, and explosion. Electricity may produce other hazards indirectly. For example, when electricity energizes equipment, mechanical hazards may result. Some electrically powered devices produce harmful levels of X rays, micro-waves, or laser light. Certain equipment may create dangers from magnetic fields. Haddon s energy theory (see Chapter 9) helps people analyze electrical hazards and identify controls. 

The Construction (Health, Safety and Welfare) Regulations 1996 deal with the main hazards likely to be found on a construction site. In addition to these specific hazards, there will be the more general hazards (e.g. manual handling, electricity, noise etc) which are discussed in more detail in other chapters. The hazards and controls identified in the Construction Regulations are as follows. 

The work activity includes operation, use and maintenance. Those responsible for the work, and those engaged in it, need to be competent to appreciate the electrical hazards and the control measures needed to minimise the risks to an acceptable level these issues are addressed in Regulations 14 and 16. To this end, the person responsible for managing the work should consider the work activities, the risks that arise, the measures that should be taken to control them, and who should be allowed to perform them. If, for example, work has to be done on a low voltage system which necessitates it being made dead , the supply to it needs to be isolated, the isolator locked off and a test made to prove that the isolated part is indeed dead and therefore safe to work on. Anyone authorised to carry out these safety precautions has to be familiar with the system, knowing which isolator or isolators to open and lock off and how to apply the test. The responsible person should also ensure that those who do the work have appropriate technical knowledge to do it properly and, on completion, to test it to prove its safety. 

Environmental Condition for Process Measurement and Control Systems Temperature and Humidity Electrical Instruments in Hazardous Locations, Ernest C. Magison, 1978... 

Other inspection services available include the examination of steel structures (new and existing), electrical wiring installations, containers (to meet Statutory Instm-ment No. 1890), dangerous substances (carriage by road in road tankers or tank containers) to meet Statutory Instmment No. 1059, examination of second-hand plant prior to purchase, plant undergoing repair or modification, the Control of Industrial Major Accident Hazard Regulations (CIMAH) Statutory Instmment No. 1902 and Control of Substances Hazardous to Health (COSHH) and Pressure Systems Regulations. 

Redding, R.J., "The Use of Solid State Circuitry Within Hazardous Areas", 3rd International Conference on Electrical Safety in Hazardous Environments, 1-3 Dec 1982, pages 219-233 Weatherhead, D., "Intrinsic Safety", Measurement and Control, Vol 10 No. 9, Sept 1977, pages 341-349... 

Optocouplers are a class of devices with input current (/ ) and output current (70) coupled optically, but isolated electrically. They are used extensively in the automation industry and in laboratory equipments where large common-mode noise/voltage or hazardous electrical shocks are present in circuits between transducers detectors and controlling equipments. The simplest optocoupler is composed of an LED (input) and a photodiode (output) as shown in Figure 1.19. 

I-3.6.2 Electronic control, monitoring, and hydrogen gas measurement equipment shall be properly grounded and isolated from piping to help prevent overpressure/ accidental shutoff situations caused by equipment failure due to lightning strikes and electrical transients and to prevent safety hazards caused by fault currents. Electrical isolation equipment for corrosion control purposes should not be installed in buildings unless specifically designed to be used in combustible atmospheres. 

Another kind of electrical equipment suitable for use in hazardous locations is equipment whose maximum possible energy output is insufficient to ignite the hazardous material. The electrical input to this equipment must be controlled by a specially designed electrical barrier. Such electrical equipment must be compatible. ANSI/UL913 defines low energy intrinsically safe electrical equipment and associated apparatus permitted in Division 1 areas. Nonincendive electrical equipment is permitted in Division 2 locations. Table 7-6 describes intrinsically safe and nonincendive equipment and identifies permitted uses. 

Where it is possible for flammable or toxic gas or vapor released within a hazardous area to migrate to the inlets for HVAC systems serving nonhazardous enclosed areas such as control rooms, detection systems should be installed in those HVAC inlets or connecting ductwork. Detection should be provided in HVAC system intakes if the building, room, or enclosure served is not electrically classified and a flammable (or toxic) gas or vapor could feasibly be drawn into the area, either by mechanical ventilation systems or by differential pressures. The detection system should alarm and automatically shutdown the HVAC to prevent gas or vapor concentration in the protected space from reaching the flammable or toxic range. 

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