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STANDARD OPERATING CONFIGURATION
The Standard Operating Configuration (SOC) is the position at which the
hood sash should be placed when the hood is actually in use as a containment
device. Making such an assumption is unavoidable when designing a fume
hood exhaust system since determines the quantity of air the system must
exhaust if an adequate face velocity is to be maintained.
In order to obtain the recommended 100 fpm face velocity, many fume hoods
have an SOC which is less than a fully open sash. If a hood user does
not use the hood with the sash at the SOC position, it is possible for
that user to create a situation in which an otherwise properly operating
hood has an insufficient face velocity.
Each chemical fume hood at the University has an assigned Standard Operating
Configuration. A schematic drawing of this configuration is posted on
the hood face. Examples of the posted schematics are shown below. Listed
below are brief descriptions and the SOC’s of several styles of fume hoods
commonly found at the University. Questions about the SOC of a specific
hood may be addressed to the Office of Environmental Health and Safety.
1.
Vertical Sash - a single vertical rising sash with a maximum
face opening about 30 inches high. This style is sometimes modified
as a distillation hood, in which case the maximum face opening is greater.
The SOC is a fully open sash, unless the hood is alarm equipped. Then
the SOC is the point just before the alarm is engaged.
SOC for Vertical and Double Vertical Sash (numbers are measuring
points)
2. Double-Vertical Sash - two
vertical rising sashes side-by-side. The SOC is generally both sashes
fully open. A few older installations may have an SOC of one sash
closed and the other fully open.
3.
Horizontal Sash - two or more horizontal sliding sashes.
The height of the face opening is approximately 30 inches and the maximum
opening width is 1/3 to ½ of the width of the hood. This style
hood is rarely equipped with an air by-pass. It is sometimes modified
as a chromatography hood, in which case the height of the face opening
is greater. The SOC is the largest opening that can be obtained without
removing any sashes from their tracks.
SOC for Horizontal Sash (numbers are measurement points)
4
. Combination
Sash - a vertical rising sash in which two or more horizontal
sliding panels are mounted. The SOC is a fully raised sash with horizontal
panels fully closed, unless the hood is alarm equipped. Then the SOC is
fully closed horizontal panels with the vertical sash raised to just below
the point at which the alarm is engaged. A few old installations have an
SOC of vertical sash down, horizontal panels open as much as possible without
removing them.
5. Walk-In
Hood - a maximum face opening six feet or more high and extends
to floor level. At Princeton, this style is usually equipped with two
vertical rising sashes mounted in parallel tracks and each capable of
closing half the face opening. The SOC is one half of the face open. 6. California
Hood - a free standing bench top enclosed on all sides by transparent
material for a height of four feet or more above the bench, and ventilated.
Horizontal sliding doors provide access from two opposite sides. The SOC
is all doors closed. 7. Triple-Vertical
Sash - three adjacent vertical-rising sashes, the center one of which
is 18" wide, in an otherwise standard vertical sash hood. The SOC is center
sash down and sashes on both sides fully raised.
SOC for Triple Vertical Sash (numbers are measurements points)
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