Tanks, open-surface

Push-Pull Ventilation of Open Surface Tanks 944... 

Rim exhausts are a specific application of slot hoods, which in turn are a type of exterior or capture hood. Rim exhausts are slot hoods placed along the rim or edge of an area source such as an open surface tank or vessel opening. Open surface tanks are widely used in indu.strial settings for cleaning, stripping. 

The rim exhaust is a source of suction that is placed along one or more sides of the area source. Air is drawn across the surface of the source and contaminated air is drawn into the hood. Specific examples of rim exhaust include open-surface tank exhaust such as electroplating, cleaning, degreasing table exhaust such as mortuary tables and exhaust used during container filling such as barrel filling. 

Rim exhausts are suitable for area sources of contaminant. They are limited in the area over which they can draw with adequate velocity. In practice, the slot hood should be within 0.6 m of the far edge of the source. For an open surface tank this means that a slot hood on one long side is necessary for tanks up to 0.6 m in width hoods on both long sides are necessary for tanks up to 1.2 m in width and rim exhaust is not practical for tanks wider than 1.2 m. For those situations, push-pull ventilation or enclosure type hoods are recommended.- ... 

Rim exhausts are slot hoods located on or around the edge of a source such as an open surface tank. Flanges may be added to decrease the airflow from behind the slot (uncontaminated air) and therefore increase the airflow from in front of the slot (contaminated air). The plenum downstream of the slot, if located above the slot, may act as a flange. Flanges may also be added to the sides of the source (tank) away from the slot hood. These flanges also act to increase the flow of contaminated air into the tank. Tank flanges, however, may interfere with process activities by limiting access to the tank. 

For a push-pull system, the source is usually an open surface tank and the airflow acts as a horizontal curtain above the surface. In this case, the person could be anywhere as long as the system works as intended and the curtain is not broken. The curtain will be broken when parts or material are lifted out of or placed into the bath and the contaminants could be spread either through convection or because the supply air blows against the material or part. 

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. 

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. 

The ACGIHi" gives guidelines for the minimum capture velocity, V p, which must be induced to move a contaminant toward an exhaust. The recommended value depends on the industrial process and the local conditions, and Table 10.12 shows the recommendations for typical open-surface-tank processes. 

The system with a horizontal jet (Fig. 10.92) is similar to the push-pull system used on open surface tanks (Section 10.4.3). One difference is that in this system the jet functions as an injector, whereas in push-pull systems the main function is as a curtain. 

Open surface tanks having canopy hoods used for ... 

Note that in the surface intergral, we mentioned a function that applies on the surface of the solid. To have a visualization of this concept, consider a tank with water entering and leaving it. The function that would apply on the surface of this tank could be the velocity of the water that enters it and the velocity of the water that leaves it. (The places where the water enters and leaves the tanks are surfaces of the tank, where holes are cut through for the water to enter and leave. The other portions of the tank would not be open to the water thus, no function would apply on these portions.) The surface integral could then be applied to the velocity functions upon entry and exit of the water. 

Figure 10.43 Lateral exhaust system for an open surface treatment tank. Source Reprinted from Daly BB, Woods Practical Guide to Fan Engineering, Woods of Colchester (a GE Company) Sheffield 1973, 3 ed., 72, 1992. By kind permission of Flakt Woods Ltd 2004.

Who All employees working in and around open-surface tank operations must be instructed on the job s hazards and the personal protection and first aid procedures applicable to these hazards. A trained stand-by employee with a suitable respirator must be present when it is necessary to enter a tank which may contain a hazardous atmosphere. 

Open surface tanks (immersion of materials in liquids for cleaning or finishing the material). 

Construction work can pose all kinds of contaminants in the air. It s the nature of activities like sandblasting, grinding, polishing, buffing, spray finishing, and working over open surface tanks to clean or finish material. The following table lays out various types of contaminants ... 

Know the locations of hazards. These may include open surface tanks, welding areas, and... 

EXAMPLE 2.7-7. Rate of Flow from a Nozzle in a Tank A nozzle of cross-sectional area A2 is discharging to the atmosphere and is located in the side of a large tank, in which the open surface of the liquid in the tank is // m above the center line of the nozzle. Calculate the velocity 1)2 in the nozzle and the volumetric rate of discharge if no friction losses are assumed. 

Does the facility have spray booths, spray rooms, or open surface tanks used for cleaning ... 

On open-surface tanks where ventilation is used to control potential exposure to employees, ventilation must be adequate to reduce the concentration of the air... 

Classification of open-surface tank operations. (i) Open-surface tank operations shall be classified into 16 classes, numbered A-1 to D-4, inclusive. 

Control means other than ventilation. Tank covers, foams, beads, chips, or other materials floating on the tank surface so as to confine gases, mists, or vapors to the area under the cover or to the foam, bead, or chip layer or surface tension depressive agents added to the liquid in the tank to minimize mist formation, or any combination thereof, may all be used as gas, mist, or vapor control means for open-surface tank operations, provided that they effectively reduce the concentrations of hazardous materials in the vicinity of the worker below the limits set in accordance with paragraph (i)(2) of this section. 

Who Train employees who work in and around open-surface tank operations in appropriate first aid procedures... 

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