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Exhaust hood ventilation

The following equations separately outline calculating contaminant concentration inside a room with central and local recirculation. The assumptions for the room are that it has one main ventilation system with supply and exhaust air and that the contaminant concentration is the same in the whole volume (except very close to the contaminant source or in the ducts, etc.). The contaminant source is steady and continuous. The model for local ventilation assumes also one main ventilation system to which is added one local exhaust hood connected to a local ventilation system (see Chapter 10) from which all the air is recirculated. In the central system the number of inlets and outlets could vary. The flow rates are continuous and steady. [Pg.613]

Local ventilation in industry usually differs from the description above in that it is connected to a local exhaust hood (Chapter 10), which has a capture efficiency less than 100%. The capture efficiency is defined as the amount of contaminants captured by the exhaust hood per time divided by the amount of contaminants generated per each time (see Section 10.5). Figure 8.3 outlines a model for a recirculation system with a specific exhaust hood. Here, the whole system could be situated inside the workroom as one unit or made up of separate units connected with tubes, with some parts outside the workroom. For the calculation model it makes no difference as long as the exhaust hood and the return air supply are inside the room. [Pg.617]

There are many possible ways to classify local ventilation systems. When local ventilation is used to describe exhaust hoods only, one classification is hoods that totally surround the contaminant source (enclosing hoods), hoods that partially surround the contaminant source (partially enclosing hoods), and hoods where the contaminant source is outside the hood (exterior hoods). A similar classification is used here for the exhaust hoods. Since local ventila tion, as described in this chapter, includes more than exhaust hoods, the following three main categories are used exhaust hoods, supply inlets, and combinations of exhaust hoods and supply inlets. (See Fig. 10.1.)... [Pg.812]

To choose a supply inlet as the local ventilation system is not common because it is difficult to design for the specific spreading of contaminants. This is usually easier with an exhaust hood. However, there are moments when large flow rates or specific flow fields are necessary to transport contaminants or for shielding from contaminants. [Pg.916]

For large open surface tanks where access for machinery or operators is required above the tank, the options for ktcal ventilation are limited. An over-head canopy would block access, and an exhaust hood placed at the side of the tank is prohibitively expensive for tanks greater than about 0.6 m across. [Pg.944]

Push-pull ventilation systems for open surface tanks consist of two components the push flow is generated by a jet or series of jets that are blown across the surface of the tank towards an exhaust hood along one side of the tank, which pulls and removes the fluid from the jet containing the contaminant. This is shown schematically in Fig. 10.69. [Pg.944]

This section deals mainly with side push-pull ventilation. Center push-pull ventilation is also sometimes used, where two jets of air are blown from a central pipe towards two parallel exhaust hoods at opposite ends of the tank. Much of what vve say about side push-pull systems is equally valid to center push-pull. [Pg.944]

More recently, in the middle 1990s, the UK s Health and Safety Executive (HSE) also reviewed the push-pull system. Hollis and Fletcher offer a comprehensive literature review on push-pull ventilation and note that the main conclusions of previous work on push-pull ventilation of tanks are that the control is primarily supplied by the inlet jet, forming a wall jet along the surface of the tank, and that the main purpose of the exhaust hood is to remove the air and contaminant contained within the push jet. [Pg.945]

FIGURE 10.107 Room mass balance boundaries for a contaminant source, local exhaust hood, and general ventilation."... [Pg.1016]

P. V. Nielsen, U. Madsen, D. J. Tveit. Experiments on an exhaust hood for the paint industry. In Ventilation 91 3rd International Symposium on Ventilation for Contaminant Control (eds. R. T. Hughes, H. D. Goodfellow, G. S. Rajhaus. Cincinnati, 1991. [Pg.1195]

Position the instrument in a well ventilated room or exhaust hood and connect compressed air source with water and hydrocarbon traps to the air distribution system of the instrument. [Pg.542]

Glazes should be prepared where adequate ventilation is available. If glazes are routinely prepared from powders, a face mask should be used. Another option, if available, is to use a plain-opening exhaust hood or wear a toxic-dust respirator approved by the National Institute for Occupational Safety and Health. Also, gloves should be worn during the preparation and application because glaze substances can be irritating to the skin. [Pg.356]

Ventilation and exhaust, hoods, ducts, blowers, filters, and scrubbers should he provided and kept in order, clean, and operational, to remove air particulates or toxic chemicals. [Pg.45]

Ventilation is an important method of reducing the level of toxic airborne contaminants in the process environment. Ventilation includes general (dilution) ventilation and local exhaust (vent) ventilation. General ventilation involves dilution of air and hence the term dilution ventilation. Local exhaust ventilation is a method of removing contaminants before they enter the workplace air. Local ventilation is typically achieved by employing a hood that covers the specific area of contamination. [Pg.766]

Ventilation — Exhaust hoods at the arc, fans, and open spaces all help to reduce the concentration of hazardous fumes, gases, and dusts, and prevent the accumulation of flammable gases, vapors, and dusts that could cause fire. Know the symptoms of fumes and gases and get out of the area if they develop. Perform atmospheric tests. [Pg.931]

Protection from isocyanate vapours liberated during polyurethane manufacture is usually achieved by installing permanent exhaust ventilation units which either exhaust directly to the atmosphere or pass their exhaust fumes through scrubbers which extract the isocyanate vapour through a sodium carbonate spray tower before atmospheric exhaustion occurs. Continuous vertically positioned exhaust hoods are common where continuous conveyor lines are involved for localized extract situations, vertical down-draught or horizontal extract modes are much safer for operatives, being designed to remove all isocyanate vapour away from an operative s face and body. These latter situations apply particularly in the manufacture of cast-moulded and reaction-injection moulded products. [Pg.414]

Fume cupboards, slot captor or receptor hood ventilation. These must be driven by a suitable and adequate fan, and will often need water wash, dust filtration or precipitators built in. Local air pollution control requirements may require capture of vapours, which cannot simply be discharged fiom an exhaust vent. The ventilation system pressures should be checked regularly to spot obstmctions or reductions in fan performance, and the pressure figures recorded. [Pg.375]

Since arsine is an extremely toxic and flammable gas, appropriate precautions must be taken in its storage and handling. Store and use arsine and arsine mixtures only in ventilated gas cabinets, exhaust hoods, or highly ventilated rooms that supply a large volume of forced air ventilation. Explosion-proof forced draft gas cabinets or fume hoods are recommended. Use piping and equipment adequately designed to withstand the pressures to be encountered. [Pg.271]

Make sure the work area is well ventilated. As a minimum, a portable exhaust hood should be placed over the welding area. [Pg.228]


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See also in sourсe #XX -- [ Pg.852 , Pg.853 , Pg.854 , Pg.855 , Pg.856 , Pg.857 , Pg.858 , Pg.859 , Pg.860 , Pg.861 , Pg.862 , Pg.863 , Pg.864 ]




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