Hazards cell room

Safety systems and protective equipment are covered in Chapter 16. The present chapter discusses buildings, electrical systems, piping, control systems, auxiliaries such as the equipment used to transport electrolyzers and their components, and the hazards associated with cell rooms. 

The operating temperature of some electrolyzers is close to 100°C, and buswork temperatures are similar. The total amount of heat generated in a cell room by convection and radiation therefore is quite large. Besides the high temperatures of process fluids and equipment, the thermal hazards in the cell area may include prolonged exposure of personnel to high ambient temperatures. Summertime cell room temperatures in hot climates can reach 50°C. This fact is a major consideration in the decision to place a cell room outdoors. When the cells are placed in a building, the heat is removed by ventilation. 

The hazards characteristic of a cell room are the electrical hazards. These carry the danger of electrocution and other damage to the human body, and they play a role in some of the thermal and explosion hazards. The thermal hazard of hot buswork has in fact been responsible for more injuries than the electrical hazard. Chlorine Institute... 

Outside the cell room itself, the transformers and rectifiers may be indoors or outdoors but always are enclosed to restrict entry to their immediate vicinities. The hazards are the high supply voltage itself, the possibility of explosion, and the risk of flash bums in case of a ground fault. The maintenance of this equipment and associated circuit breakers, switches, and relays is a subject for specialists, and other personnel should not enter the enclosures while equipment is activated. 

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. 

One does not design a cell room to achieve a certain steady-state or 1-hr peak level of chlorine concentration in the air, nor does one attempt to establish a priori a tolerable exposure profile for plant personnel. Tables such as 8.6, in spite of the apparent precision of the numbers, are really qualitative or at best semi-quantitative indicators of the seriousness of a hazard. Designers of chlorine-handling plants must exercise proper care by designing to recognized industry standards, and operators must understand and observe established procedures. There is more on this subject in Section 16.2.1. 

There is also the question of electrical classification of cell rooms. As noted in Section 8.5.1, most cell rooms are not classified as hazardous when the appropriate precautions for venting of hydrogen have been made. This remains an issue to be decided for each plant on its own merits. 

In the long run, spills of process fluids are nearly inevitable. These create slipping hazards and can also short out insulation. Cell room housekeeping is therefore very important. Floor gratings, besides being nonconductive, should also have nonslip properties. FRP and timber have been widely used. The former is the material of choice in most modem cell rooms. 

The retirement of mercury-cell plants has created a new issue, the disposal of their mercury inventory. This has been considered a waste by some. However, mercury remains a useful commodity and automatically regarding it as a hazardous waste may be counterproductive [96]. Handling of mercury is an issue that requires an accepted societal policy. The metal is available from strategic reserves, retired or converted cell rooms, and reclamation processes. Total stocks worldwide are estimated roughly to be 25-50,000 tons [97]. The gradual run-down of mercury inventory before retiring a plant is not a useful technique. The opposite approach, increasing the amount of mercury in the cells, has in fact been used in older plants to improve cell performance and reduce the loss of mercury to the environment [98]. 

Operation under pressure would seriously aggravate the consequences of a chlorine leak in the cell room. Outdoor construction or the use of some of the practices associated with contained storage systems (Section 9.1.8.2C) would help to relieve the hazard. In any event, there would have to be a complete rethinking of many operating practices as well as major revisions in design. 

One approach where the analyzer is housed within a more benign environment is based on the use of an optical fiber-based sample interfacing. As an example the analyzer may be located within the plant control room, possibly within a standard 19-inch (48 cm) electronics rack. With this type of configuration the sample cell and sample conditioning system are placed within the hazardous location and the instrument is located in a general purpose, or a safe area, where the optical fibers are used for the analyzer-sample cell/sampling... 

Motor Evaluation. Many different operations are performed in propellant and motor evaluation. The main safety precaution is to keep personnel contact to an absolute minimum. Most operations are performed remotely, the only contact required being during assembly and installation or removal of the test device. The most hazardous operation, test firings, are performed remotely in reinforced concrete barricaded cells (see figure 2). The technician who connects the ignition circuit, the last operation before firing, retains the key to the firing circuit such that it cannot be activated until he returns to the control room. 

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