Fume Hood Airflow Types

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. 

Fume and Mist Respirators. All the applicable parts of this system must apply to these respirators, with the added requirement that the noise level generated by the respirator measured inside the hood or helmet at maximum airflow shall not exceed 80 dBA. A second type of powered filter respirator is mounted on a belt with the complete motor and filter unit. The hose from the filter unit extends to a full-face respirator style and provides a sufficient flowrate. Powered air-purifying respirators have the advantage of mobility and can be used by people who have minor... 

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