Positive pressure glove boxes

Develop and encourage safe habits and avoid unnecessary exposure to chemicals. Do not smell or taste chemicals. Vent any apparatus that may discharge particularly hazardous chemicals into local exhaust devices. Chemicals shall be properly stored and used to prevent exposure. Appropriate personal protective equipment (PPE) shall be provided to employees working in areas where hazardous substances are in use. Employees shall be trained in the safe use and maintenance of PPE provided in the laboratory. Test positive pressure glove boxes for leaks before use. Do not allow release of toxic substances into any building area, only into an appropriate local exhaust device ducted to the outdoors. 

Quantitative IR spectroscopy has turned out to be very usefid for measuring the decay of peroxide concentration or, alternatively, the inaease in the concentration of products from decomposition. Two types of discontinuous procedures have been used at lower reaction temperatures, the peroxide solution is contained in an internal cell (see Figure 3), which is filled and assembled in a glove box under an argon atmosphere. The internal cell is positioned into the optical high-pressure cell and pressurized with n-heptane acting as the pressure-transmitting medium. The assembly is heated to the reaction temperature and the collection of IR spectra is started. In the case that decomposition rate becomes too fast and a major fraction of the peroxide is decomposed before reaaion conditions of constant T and p are reached, the peroxide solution is dirertly fed into a preheated autoclave. The solution is then quickly pressurized and the collection of IR spectra is started. 

A sketch of the glove box is depicted in Fig.2.9. The pressure in the box should be maintained at a positive pressure of nitrogen. About 1.5-2 cm of oil on a manometer tube represents a satisfactory pressure and will cause the gloves to become inflated outside the box. The mercury lute acts as a safety valve and will prevent the build up of pressures greater than 1 cm of mercury in the box. 

Immediately following the initial assembly (and at any other time leaks are suspected), the box and purification train should be tested for leaks. A quick test for leaks is to pressurize the dry box until the gloves stick straight out. The gloves should remain in this position for several hours if no leaks are present. If leaks are indicated, testing is most easily accomplished while the box is pressurized. If the inert atmosphere is helium, the preferred method is the helium sniff test. All joints, welds, and connections should be checked. In the absences of a helium-sensitive probe or if the inert atmosphere is other than helium, the bubble method may be used a small amount of soapy water is placed on leak-prone welds and joints and the appearance of any bubbles is noted. 

Remove the flasks from the dry box or glove bag, and connect them to a vacuum/argon manifold. Before opening the stopcocks to the inert atmosphere from the manifold, evacuate the system (5 min) and refill with argon or nitrogen (1 min) in three cycles. Open the stopcocks to positive argon pressure. 

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