The ACGIH Manual of Recommended Practice should be used as a contemporary source of best design practices for the range of design configurations likely to be encountered in the laboratory facility. This manual is a great resource for airflow rates needed in an energy-efficient laboratory. See Sections: 6.5 Dilution Ventilation Principles; 3.2.2 Air Changes; and Table 10.35.1 below.
These dilution ventilation principles use equations to more accurately predict the hazardous effluent concentrations that are found in laboratory facility exhausts. The application of these principles can affect the exhaust stack design and its exit velocity and consequently the energy required to create a safe dispersion of the pollutants. See Chapter 6.
The issue of air changes is analyzed correctly. The standard states that "'Air changes per hour' or 'air changes per minute' is a poor basis for ventilation criteria where environmental control of hazards, heat, and/or odors is required." The impact of the laboratory's ceiling height is identified correctly as one of the reasons that the air change approach does not address adequately the required contamination control. Dilution of these environmental conditions is the alternative method. See Chapter 3, 5, and 6.
This section of the ACGIH manual references the best available research on fume hood face velocities. Table 10.35.1 gives a comprehensive review of the arrangements for incorporating fume hood face velocities from 60 to 100 fpm. See Chapter 3. [Industrial Ventilation: A Manual of Recommended Practice - 24th Edition, 2001]
Open Hood Face
|1.Ceiling panels properly located with average panel face velocity < 40 fpm. Horizontal sliding sash hoods. No equipment in hood closer than 12 inches to face of hood. Hoods located away from doors and traffic ways.*||60|
|2.Same as 1 above; some traffic past hoods. No equipment in hoods closer than six inches to face of hood. Hoods located away from doors and traffic ways.*||80|
|3.Ceiling panels properly located with average panel face velocity < 60 fpm or ceiling diffusers properly located; no diffuser immediately in front of hoods; quadrant facing hood blocked; terminal throw velocity < 60 fpm. No equipment in hood closer than six inches to face of hood. Hoods located away from doors or traffic ways.*||80|
|4.Same as 3 above; some traffic past hood. No equipment in hood closer than six inches to face of hood.||100|
|5.Wall grilles are possible but not recommended for advance planning of new facilities.|
|*Hoods near doors are acceptable if 1) there is a second safe egress from the room, 2) traffic past hood is low, and 3) door is normally closed.|