Walk-in Hoods

In general, pilot-plant space can be divided into five basic types separate buildings, containment cells or barricades, open bays, walk-in hoods, and laboratory areas. A summary of the advantages and disadvantages of each has been given (1). 

If the solvent is removed with a rotary evaporator, considerable loss of product results from codistillation with dichloromethane. The checkers found that if this exact distillation set-up was not used the yield of BTMSPO decreased substantially (30-40%) because of the codistillation of CH2CI2 and BTMSPO (observed in distillate by 1H NMR). The distillation set-up requires use of a "walk-in" hood (see diagram). 

Analytical Chemistry The Analytical Chemistry laboratory with 26 student stations contains, along one wall, two six-foot bench-mounted induced-air hoods and two six-foot walk-in hoods. These hoods are exhausted in pairs. 

Physical Chemistry/Instrumental Analysis The Physical Chemistry laboratory, containing 20 student stations, is used also for Instrumental Analysis and for certain courses in the Community and Technical College which administers two-year associate degree programs. The laboratory is equipped with three four-foot induced-air hoods and a five- and a six-foot walk-in hood, each with a built-in vacuum rack. Against one wall are located four peninsular work benches ventilated by a single canopy hood. 

My labs will have just one bench hood and one walk-in hood (Figure 3) but a number of places to connect flexible exhausts (Figure 4). The building is just being completed at the time of writing so the description must be of plans as compared to the finished product we expected to occupy during the summer. 

Pilot plant Usually constructed in a laboratory, open bay, containment cell, or large walk in hood 100,000 to 1,000,000... 

In addition, some scale-up works need apparatus that are operated for preparative purposes as well, along the lines of the kilo lab, but in a flexible environment not focused exclusively on batch processing as the kilo lab is. Examples of such apparatus are fluid bed crystallizers, hydroclones for the evaluation of that method of solid/liquid separation, lyophili-zation cabinets with special vial sampling capabilities, intermediate scale membrane processing assemblies, etc. An area well suited for such testing purposes is not only highly desirable, but often facilitates preparative work by processing methods not within the scope of the kilo lab. Such an area should be reasonably open for the manipulation of portable equipment, with ample walk-in hoods and tall California racks, well distributed utilities, portable measurement panels for recorders, fiowmeters and the like. 

Intermediate bench/pilot scale lab for engineering studies (not the kilo lab, although it can be readily pressed into preparative duty as appropriate). Multilevel open bay space, walk-in hoods, tall racks, utilities stations for rented portable equipment, very little fixed equipment... 

Figure 3.13 Leakage rate data for various size walk in hoods for different face velocities.

There are several different types of fume hoods (1) conventional hood, vertical sash, (2) conventional hood, horizontal sash, (3) bypass hood, (4) auxiliary air hood, (5) walk-in hood, and (6) self-contained hood. The differences in types 1,4, and 6 are especially important in terms of the amount of tempered air lost during operations, while 1,2, and 3 differ primarily in the airflow patterns through the sash openings. Figures 3.14 to 3.19 illustrate each of these types and the air currents through them during typical operations. In addition, there are specialty fume hoods for perchloric acid and radioisotopes, which will be treated separately. All of the hoods discussed in this section will be updraft units, where the exhaust portal is at the top of the hood, with of course, the exception of the self-contained type. 

Systems involving toxic gases should be adequately ventilated. If possible, the systems should be set up totally within a fume hood. Large walk-in hoods often are used for this purpose. All systems should be carefiiUy leak-tested prior to introduction of toxic materials into the system, periodically thereafter, and after any maintenance or modifications to the system which could affect its integrity. 

The first fume hoods were simply boxes that were open on one side and connected to an exhaust duct. Since they were first introduced, many variations on this basic design have been made. Six of the major variants in fume hood airflow design are listed below with their characteristics. Conventional hoods are the most common and include benchtop, distillation, and walk-in hoods of the constant air volume (CAV), variable air volume (VAV), bypass and non-bypass variety, with or without airfoils. Auxihary air hoods and ductless fume hoods are not considered "conventional" and are used less often. Laboratory workers should know what kind of hood they are using and what its advantages and limitations are. 

Laboratory scale" excludes those workplaces whose function is to produce commercial quantities of materials. "Laboratory-type hood" means a device located in a laboratory, enclosure on five sides with a movable sash or fixed partial enclosed on the remaining side constructed and maintained to draw air from the laboratory and to prevent or minimize the escape of air contaminants into the laboratory and allows chemical manipulations to be conducted in the enclosure without insertion of any portion of the employee s body other than hands and arms. Walk-in hoods with adjustable sashes meet the above definition provided that the sashes are adjusted during use so that the airflow and the exhaust of air contaminants are not compromised and employees do not work inside the enclosure during the release of airborne hazardous chemicals. 

The walk-in hood is a chemical fume hood that is mounted directly on the laboratory floor or a slightly raised chemical resistance platform. It is used for the ventilation of larger pieces of equipment, with the advantage that these pieces of equipment can be wheeled in and out of the walk-in hood. The walk-in hood typically uses two separate sashes. 

Walk-in Hood. There are times when a large item of equipment or an extra-tall experimental set-up must be provided with exhaust ventilation. The walk-in or floor-mounted hood is designed for this purpose (Figure 12.4). Drainage for spills in this type of hood can be provided by a floor drain or a floor pan which can be pumped out. Utilities can be provided on the side walls, and the sash is usually divided into sections to allow ease of access and operation. 

Distillation Hood. This type of hood is intermediate in size between the standard bench hood and the walk-in hood. Its oversized chamber height allows tall column setups, but the counter, which is at a height of... 

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