The face area for a hood with a combination sash is based on the opening through the horizontal siding panels. It has roughly one half the face area of the same size hood with a vertical sash. Therefore, the hood with a combination sash requires a smaller (restricted) bypass even if it is to be used for constant volume operation. In fact, having an open bypass provides no operational benefits and increases the exhaust requirement for the hood as air must be drawn through the bypass into the hood. The only time an open bypass is required is if the exhaust volume is based on the sash raised vertically rather the opening through he horizontal panels.
The fan switch requires the installation of a Square D Thermal unit to function. The thermal unit is not supplied with the switch as it must be selected based on the full load amperage of the fan motor.
|SQUARE D THERMAL UNIT SIZING|
|Motor Full-Load Current Amperes||Thermal Unit Number||Motor Full-Load Current Amperes||Thermal Unit Number||Motor Full-Load Current Amperes||Thermal Unit Number|
|0.41 – 0.44||A .49||1.57 – 1.65||A 1.86||5.36 – 5.85||A 7.65|
|0.45 – 0.49||A .54||1.66 – 1.79||A 1.99||5.86 – 6.41||A 8.38|
|0.50 – 0.53||A .59||1.80 – 1.95||A 2.15||6.42 – 6.79||A 9.25|
|0.54 – 0.58||A.65||1.96 – 2.15||A 2.31||6.80 – 7.57||A 9.85|
|0.59 – 0.65||A.71||2.16 – 2.38||A 2.57||7.58 – 8.15||A 11.0|
|0.66 – 0.71||A .78||2.39 – 2.75||A 2.81||8.16 – 8.98||A 11.9|
|0.72 – 0.78||A .86||2.76 – 2.84||A 3.61||8.99 – 9.67||A 13.2|
|0.79 – 0.85||A .95||2.85 – 3.06||A 3.95||9.68 – 9.95||A 14.1|
|0.86 – 0.96||A 1.02||3.07 – 3.45||A 4.32||9.96 – 10.8||A 14.8|
|0.97 – 1.04||A 1.16||3.46 – 3.70||A 4.79||10.9 – 12.1||A 16.2|
|1.05 – 1.16||A 1.25||3.71 – 4.07||A 5.30||12.2 – 13.1||A 17.9|
|1.17 – 1.29||A 1.39||4.08 – 4.32||A 5.78||13.2 – 13.9||A 19.8|
|1.30 – 1.37||A 1.54||4.33 – 4.90||A 6.20||14.0 – 15.0||A 21.3|
|1.38 – 1.47||A 1.63||4.91 – 5.35||A 6.99||15.1 – 16.0||A 25.2|
|1.48 – 1.56||A 1.75|
|THERMAL UNIT SIZING FOR KEWAUNEE FANS|
|Kewaunee Fan||115 Volts||230 Volts|
|Model Number||Horse Power Rating||Full Load Current Amperes||Square D Thermal Unit Number||Full Load Current Amperes||Square D Thermal Unit Number|
|HFS-0902||1/4 HP||5.0||A 6.99||2.5||A 2.81|
|HFS-0903||1/3 HP||6.0||A 8.38||3||A 3.95|
|HFS-0905||1/2 HP||7.4||A 9.85||3.7||A 5.30|
|HFS-1007||3/4 HP||8.2||A 11.9||4.1||A 5.78|
|HFS-1310||1 HP||12.8||A 17.9||6.4||A 9.25|
* Fan switch on Kewaunee fume hoods is rated for 1 HP motors or less
The indented portion of the work top defines the safe working area of the hood where contaminants can be generated without exposing the hood user. This safe working area starts 6″ behind the sash opening. The hood user is likely to be exposed to any contaminants generated in front of this safe working area due to the eddies in front of the use’s body.
They are located on the right vertical facia behind the top front panel.
Normally the hood face velocity is measured with the sash fully open. However, if the hood has a gravity sash stop (Option 8) or a sash label (F-4803-00) to indicate the safe sash height, the face velocity should be measured with the sash at the stop or label.
No, the face velocity on an open bypass hood will increase as the sash is closed. The bypass limits the increase in face velocity to no more than three and a half times the velocity with the sash closed. This allows the hood to maintain a constant exhaust volume flow rate.
No, according to NFPA 45 Fire Protection for Laboratories Using Chemicals, laboratories and hoods are unclassified electrically with respect to Article 500 of the National Electrical Code. Where there is an extraordinary hazard, the user may wish to use explosion-proof electrical fixtures for added safety.
The most widely used standard for testing hoods is the ASHRAE 110 Method of Testing Performance of Laboratory Fume Hoods. This standard has sections for visualization of flow patterns, measuring face velocity, and measuring containment using a tracer gas. In addition the SEFA 1.1 Laboratory Fume Hoods Recommended Practices has sections on visualizatio n of flow patterns and measuring face velocity.
OSHA does not have specific requirements for fume hood face velocity. The most widely accepted references on this subject ANSI/AIHA Z9.5 American National Standard for Laboratory Ventilation and the National Research Council’s Prudent Practices in the Laboratory recommend face velocities of 80 to 120 feet per minute (FPM).
Usually the hood is connected to a single 120 volt, 20 amp circuit. 12 gage THHN solid strand wires in flexible metallic conduit is generally acceptable.
For a typical wiring diagram for a hood:
Yes, in most instances it is preferable to have the alarm deactivated when the hood exhaust fan is off. If the hood fan is off and the alarm is powered, the air currents created by people walking past the hood may cause the alarm to momentarily go to “NORM”. When the air current subsides the audible alarm will activate again. Many people find this annoying.
The fan should be remote from the hood, either on the roof or a penthouse. In facilities with many hoods, several hoods may be connected to a one exhaust fan.
The most often used material for exhaust ducting is stainless steel. It has good chemical resistance and is noncombustible. For highly corrosive applications PVC is often used. PVC is combustible and should be used in such a manner that it does not compromise the fire protection of the lab. For noncorrosive applications, galvanized steel may be used.
Kewaunee hoods that are wired at the factory and contain only the following devices are listed under the UL 61010A-1 standard. These devices are: 120 volt, 20 amp GFCI receptacles, 240 volt, 20 amp duplex receptacles, light switches, fan switches and the Kewaunee Air Alert Alarm. Hoods that contain other devices or hoods that are not wired at the factory are not UL listed. All devices provided on Kewaunee hoods are UL listed.
In addition, fume hoods with Kemglass or Stainless Steel liners are listed under the UL 1805 standard.
An acid storage cabinet vented through the hood work top will have an exhaust flow rate of approximately five to ten cubic feet per minute (CFM).
As a general rule, no. The NFPA 30 Flammable and Combustible Liquids Code discourages the venting of flammable storage cabinets. The purpose of the cabinet is to protect the contents of the cabinet from a fire in the lab. It is difficult to vent a cabinet without compromising its fire protection.
For more information consult one of the following publications or organizations.