Basic Documentation

Applicable Definitions (Alphabetical Listing)
Siemens Industry, Inc. 9
Term Definition Commentary
Flow Tracking
(Airflow Tracking)
Fume
Gas
Fume Hood
Fume Hood:
Airfoil
A method of maintaining a room under either a ‘negative’ or ‘positive’ pressure.
Laboratory rooms are normally required to be under negative pressure which means
that the room is deliberately kept a slight vacuum with respect to the corridor and/or
surrounding area. (Also see the definition for ‘Pressurization’.) In this condition, air and
contaminants generally migrate into the laboratory from the surrounding spaces, rather
than outward. Flow tracking (to maintain negative pressure) consists of carefully
controlling the ventilation system so that the fresh air being supplied to the room will
always be a certain amount less than the total amount of air exhausted from the room.
Small solid particles formed by the condensation of vapors of solid materials.
A formless fluid which tends to occupy the entire space in which it is released.
A ventilated enclosure designed to contain and remove fumes, gases, vapors, mists,
and particulate matter generated within the hood interior. A fume hood must be
integrated with a properly designed laboratory ventilation system that includes a
provision for exhausting the fume hood interior and supplying fresh air to the laboratory
room to replace the air exhausted from the fume hood. When properly used and safe
laboratory work practices are followed, a fume hood enables the user to manipulate
chemicals and associated apparatus without being exposed to harmful fumes. There
are several d
ifferent fume hood designs which are intended to meet specific needs. This
document describes their inherent characteristics and the requirements which various
safety standards impose for safe utilization.
A horizontal slightly angled, shelf-like protrusion on the front exterior of a fume hood that
extends outward a few inches from the fume hood face and is typically just above the
level of the fume hood’s interior work surface. Its purpose is to create a ‘streamlined’
airflow over the work surface within the fume hood. It also serves to keep the fume hood
user several inches back from the fume hood face opening for added safety. Airfoils
usually have a narrow slot along the full width of their underside to ensure that some air
always sweeps across the fume hood’s work surface even when the sash is fully closed.
Experience has demonstrated that Flow
Tracking is the preferred method of
maintaining control over room pressure.
Other control methods such as those based
upon actual sensing of room pressure are
normally less stable and require appreciably
more time to react to changing conditions.
A “fume hood” is intended to provide an
enclosure
for the safe manipulation of
chemicals and gases. This differentiates it
from other various types of hoods such as
canopy hoods or slot hoods which are
primarily intended to remove heat, water
vapor, offensive odors, dusts and in general
non-hazardous ‘fumes’. These exhaust
provisions do not provide the same level of
protection and are not a substitute for and
should not be used in place of a fume hood.
Note that the various safety standards quoted
in this document often utilize slightly different
terminology (such as: chemical hood,
chemical fume hood, laboratory chemical
hood, laboratory fume hood, fume cupboard,
etc.) for what is most commonly referred to as
a “fume hood”. For consistency the generic
term fume hood
is always used in this
‘Commentary’ column.