SELECTING
EXHAUST RATES FOR O.S.H.A. CONFORMANCE
1. Obtain recommended control velocity required for the selection
operation from Table 1 below.
2. Determine CFM per square foot based on this control velocity and
on tank width to length ratio using Table 2.
3. Calculate exhaust rate as product of CFM per square foot and tank
surface area. |
Table 1
Minimum Control Velocity
|
OPERATION
|
CONTROL
VELOCITY
|
SCRUBBER
RECOMMENDED
|
|
PLATING
|
Cadmium
|
50
|
- |
|
Chrome
|
150
|
X
|
|
Copper
|
75
|
X
|
|
Tin
|
75
|
- |
|
Zinc
|
75
|
- |
|
ANODIZING |
Sulfuric
|
100
|
X
|
|
PICKLING
|
Nitric
|
150
|
X
|
|
Sulfuric
|
100
|
X
|
|
Hydrochloric
|
150
|
X
|
|
Nitric/Hydrofluoric
|
150
|
X
|
|
|
OPERATION
|
CONTROL
VELOCITY
|
SCRUBBER
RECOMMENDED
|
|
CLEANING
|
Caustic
or Electrolitic (not boiling)
|
75
|
|
|
Caustic
or Electrolitic (boiling)
|
100
|
X
|
|
BRIGHT
DIP
|
150
|
X
|
|
STRIPPING
|
Nitric
|
150
|
X
|
|
Sodium
Hydroxide
|
75
|
X
|
|
Sulfuric
|
75
|
X
|
|
HOT
WATER
|
Not
Boiling
|
50
|
- |
|
Boiling
|
75
|
- |
|
|
Table 2 Minimum
Rate, CFM/Square Foot of Tank Area for Lateral Exhaust
Required
Minimum
Control Velocity (fpm) |
CFM
per Sq. Ft. to Maintain Required Minimum Control Velocities
at Following:
tank width (W) / tank length (L) — ratios |
| 0.0
- 0.09 |
0.1
- 0.24 |
0.25
- 0.49 |
0.5
- 0.99 |
1.0
- 2.0 |
| Hood
along one side or two parallel sides of tank* when one hood
is against a wall or baffle. Also for a manifold along tank
centerline.* |
| 50 |
50 |
60 |
75 |
90 |
100 |
| 75 |
75 |
90 |
110 |
130 |
150 |
| 100 |
100 |
125 |
150 |
175 |
200 |
| 150 |
150 |
190 |
225 |
250 |
250 |
| Hood
along one side or two parallel sides* of free standing tank
not against wall or baffle. |
| 50 |
75 |
90 |
100 |
110 |
125 |
| 75 |
110 |
130 |
150 |
170 |
190 |
| 100 |
150 |
175 |
200 |
225 |
250 |
| 150 |
225 |
250 |
250 |
250 |
250 |
*Use W/2
as tank width in computing when manifold is along centerline or two
parallel sides of tank. |
RECOMMENDED
OPEN SURFACE TANK DESIGN DATA AND EXHAUST VOLUME REQUIREMENTS FOR
O.S.H.A. CONFORMANCE
General Design
Data:
- Duct velocity
– 2,000 to 3,500 fpm.
- Hood entry
loss – 1.78 times slot VP plus duct entry loss.
- Maximum
plenum velocity – 2,000 fpm.
- Slot velocity
– 3,000 fpm.
- If hood
length is 6 ft. or greater, multiple take-offs are desirable.
If hood length is 10 ft. or greater, multiple take-offs are necessary.
- Tank width
(W) is the distance over which the hood must
pull air to operate. This should not exceed 30". Wider tanks
require a hood on each side or use of push-pull system.
- Liquid level
should be at least 6" below the bottom of the hood slot.
|
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