Basic Documentation

Fume Hoods
Siemens Industry, Inc. 25
Topic Requirement(s) Commentary
Size & ADA
Compliance
U.S. OSHA, 29 CFR, Part 1910, Occupational Safety and Health Standards,
Subpart Z, Toxic and Hazardous Substances,1910.1450,C4(b):
A laboratory hood with 2.5 linear feet of hood space per person should be provided
for every 2 workers if they spend most of their time working with chemicals.
U.S. ADA, 28 CFR Part 36
New facilities constructed and occupied after January 26, 1993 must be constructed
to make them “readily accessible” to and usable by persons with disabilities.
Any existing facility that undergoes major alterations or renovations after January 26,
1992 must be “readily accessible”...unless the cost of compliance is disproportionate
to the overall cost of the alterations.
Fume hoods must accommodate laboratory
workers with physical impairments. This
includes allowing variations in workbench
height, wheel chair accessibility, and easier
access to hood controls (electrical switches,
valves, sash, safety devices, etc.).
CAV
(Constant Air
Volume)
Bypass
American National Standard for Laboratory Ventilation, ANSI/AIHA Z9.5-2003
3.2.1 Bypass hoods are laboratory hoods with either vertical or horizontal moving
sashes that shall meet the requirements of 3.3. (3.3 requires adequate face velocity,
periodic face velocity measurement and an airflow measuring device on the hood.)
The face velocity of the hood opening should not exceed three times the nominal face
velocity with the sash fully open.
Specifically, a ‘bypass’ type fume hood is
designed to limit the variation in fume hood
face velocity that would occur as the sash
opening varies. This is done by incorporating
a ‘bypass’ or air diversion opening that is fully
uncovered when the sash is fully closed but
is progressively covered as the sash is
moved from closed to fully open. The bypass
opening is normally located in the upper
portion of the hood and covered with a grille
or louvers.
Bypass type fume hoods are typically utilized
when there is no other provision to
automatically control fume hood face velocity.
Also refer to Fume Hoods: VAV (Variable Air
Volume).
CAV
(Constant Air
Volume)
Conventional
American National Standard for Laboratory Ventilation, ANSI/AIHA Z9.5-2003
3.2.2 Conventional hoods shall meet the requirements in Section 3.3. (3.3 requires
adequate face velocity, periodic face velocity measurement and an airflow measuring
device on the hood.) The hood exhaust volume shall remain unchanged with the sash
in full open or in the design open position. As the sash is lowered, the face velocity
will increase. In the fully closed position, airflow would be through the airfoil only.
California OSHA – Division of Occupational Health & Safety (DOSH) Subchapter
7. General Industry Safety Orders, Group 16. Control of Hazardous Substances,
Article 107. Dusts, Fumes, Mists, Vapors and Gases
5154.1. Ventilation Requirements for Laboratory-Type Hood Operations:
When flammable gases or liquids are used, or when combustible liquids are heated
above their flashpoints, hoods shall be designed, constructed, and installed so that
hood openings at all sash positions provide sufficient airflow to prevent ignitable
concentrations.
A ‘conventional’ fume hood is the most basic
design and has no provision to maintain a
constant face velocity or even to limit the
variation in face velocity that occurs as the
sash opening changes. Conventional fume
hoods have limited application since the face
velocity variations do not conform to current
safety requirements. See Fume Hood: Face
Velocity on the pages that follow.