Basic Documentation

Fume Hoods
Siemens Industry, Inc. 31
Topic Requirement(s) Commentary
Ductless
American National Standard for Laboratory Ventilation, ANSI/AIHA Z9.5-2003
4.2 Ductless hoods shall meet the general requirements of Section 3.1 and 3.3 as
applicable. (3.1 requires hood construction be adequate and 3.3 requires adequate
face velocity, periodic face velocity measurement and an airflow measuring device
on the hood.)
Ductless fume hoods shall have signage prominently posted on the ductless hood to
inform operators and maintenance personnel on the allowable chemical used in the
hood, type and limitation of filters in place, filter changeout schedule and that the hood
recirculates air to the room.
Ductless fume hoods should only be used with
quantities and types of chemicals that do not
pose a health hazard and where the exhaust
filter media can remove any particulate
released within the hood. In general ductless
fume hoods are only suitable used when the
chemicals pose an annoying odor rather than
a health hazard and/or where airborne dust is
generated.
Auxiliary Air
National Fire Protection Association, Standard NFPA 45, 2011
8.8.6 For auxiliary air fume hoods, auxiliary air shall be introduced exterior to the
hood face in such a manner that the airflow does not compromise the protection
provided by the hood and so that an imbalance of auxiliary air to exhaust air will not
pressurize the hood interior.
A.8.13.1 The operating characteristics of some chemical fume hood designs,
particularly auxiliary air chemical fume hoods, change at intermediate positions of
sash height. It is, therefore, important to verify inward airflow over the face of the
hood according to 8.13.1(5) at several sash heights from full open to closed.
American National Standard for Laboratory Ventilation, ANSI/AIHA Z9.5-2003
3.2.3 Auxiliary air hoods are laboratory hoods that 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.)
In addition:
• The supply plenum shall be located externally and above the top of the hood
face; moreover, the auxiliary air shall be released outside the hood.
• The supply jet shall be distributed so as not to affect containment.
• The auxiliary air shall not disrupt hood containment or increase potential for
escape.
Scientific Equipment & Furniture Association
SEFA 1–2006 Recommended Practices for Laboratory Fume Hoods
4.2.6 Auxiliary Air Fume Hood
The auxiliary air system, when added to a standard laboratory fume hood, shall
function to reduce the consumption of conditioned room air. The auxiliary air is
typically introduced exterior to the fume hood and enters the fume hood through the
face with the sashes open.
With the sash(es) closed auxiliary air shall be drawn into the fume hood interior in
such a manner as to aid in the dilution of heat and fumes generated in the work area.
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Auxiliary air fume hoods are generally CAV
type fume hoods that have a supply air outlet
added to the upper portion of the front of the
fume hood to enable using unconditioned
outside air for part of the fume hood’s
ventilation air. This reduces the amount of
conditioned room air necessary to offset the
fume hood exhaust. Use of this auxiliary air is
intended to attain a reduction in the energy
needed to condition the room air.
Many safety professionals do not recommend
using auxiliary air fume hoods because of the
complications and potential problems that
usually arise. Also, many lab designers do not
consider auxiliary air fume hoods as a
worthwhile option.
Auxiliary air fume hoods have specific
drawbacks such as requiring additional fans
and ducts to bring the outside air directly to
the front of the fume hoods and can
complicate attempts to create optimum fume
hood airflow patterns. In addition, it is usually
necessary to temper the incoming outside air,
especially during extreme weather, since the
user is typically exposed to this airflow.