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Air flow in fume hood demonstrated by dry ice fog. A fume hood is typically a large piece of equipment enclosing six sides of a work area (including a movable sash window or door), the bottom of which is most commonly located at a standing work height (at least 28 to 34 inches (71 to 86 cm) above the floor).
A standard measurement, hood static pressure, provides information on airflow changes that affect hood performance. For hoods designed to prevent exposures to hazardous airborne contaminants, the American Conference of Governmental Industrial Hygienists recommends the installation of a fixed hood static pressure gauge. [8]
Fume hoods were introduced about 100 years ago to safeguard personnel working with hazardous materials. While many changes and improvements have been made, the basic concept and design of fume hoods remains the same. Air is drawn from the workplace, around the worker and into the front of the hood, and is then exhausted out of the laboratory.
Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour.
This is in contrast to a laminar flow clean bench, which blows unfiltered exhaust air towards the user and is not safe for work with pathogenic agents. [3]: 13 [4] Neither are most BSCs safe for use as fume hoods. [2] Likewise, a fume hood fails to provide the environmental protection that HEPA filtration in a BSC would provide. [5]
Choking is the condition which occurs in the compressor in which it operates at very high mass flow rate and flow through the compressor can't be further increased as mach number at some part of the compressor reach to unity i.e. to sonic velocity and the flow is said to be choked. In compressor maximum volume flow rate is limited by cross ...
Despite their similar appearance, a laminar flow cabinet should not to be confused with a fume hood. A laminar flow cabinet blows unfiltered exhaust air towards the worker and is not safe for work with pathogenic agents, [2]: 13 [3] while a fume hood maintains negative pressure with constant exhaust to protect the user, but does not protect the ...
For example, a mass flow rate of 1,000 kg/h of air at 1 atmosphere of absolute pressure is 455 SCFM when defined at 32 °F (0 °C) but 481 SCFM when defined at 60 °F (16 °C). Due to the variability of the definition and the consequences of ambiguity, it is best engineering practice to state what standard conditions are used when communicating ...
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