1. New exhaust fans should be oriented in an up-blast orientation.

_{Good Practice per Stanford University EH&S}

Any other type of fan orientation increases the fan work load and increases the risk of exhaust emission re-entrainment.

2.  Hood exhaust stacks shall extend at least 7 feet above the roof. Discharge shall be directed vertically upward.

_{CCR, Title 8, Section 5154.1(e)(4)(D)}

If parapet walls are present, EHS recommends that stacks extend at least 2 feet above the top of a parapet wall or at least 7 feet above the roof, whichever is greater.

Note: The University Architect/Planning Office must be contacted if any building feature, such as exhaust stacks, extend above the roofline.

3.  Hood exhausts shall be located on the roof as far away from air intakes as possible to preclude re-circulation of laboratory hood emissions within a building. For toxic gas applications, the separation distance shall be at least 75 feet from any intake. 

_{CCR, Title 8; Section 5154.1(e)(4)}

_{SCCo Toxic Gas Ordinance No. NS-517.44}

As future gas necessities are difficult to predict, EH&S recommends at least 75 feet for all applications.

4.  Discharge from exhaust stacks must have a velocity of at least 3,000 fpm. Achieving this velocity should not be done by the installation of a cone type reducer. The duct may be reduced, but the duct beyond the reduction should be of sufficient length to allow the air movement to return to a linear pattern.

_{ANSI Z..95-2003, 5.3.5}

_{Good Practice per Stanford University EH&S}

Strobic-type exhaust fans may be used to address exhaust velocity needs.

5.  Rain caps that divert the exhaust toward the roof are prohibited. 

_{CCR, Title 8; Section 5154.1(e)(4)}

6.  Fume hood exhaust is not required to be treated (e.g., filtered or scrubbed) except…

when one of the following substances is used with a content greater than the percent specified by weight or volume: 

_{CCR, Title 8, Section 5209(b)11}

1,2-Dibromo-3-Chloropropane

Asbestos

Vinyl Chloride

Acrylonitrile

Inorganic Arsenic

Ethylene Dibromide

Ethylene Oxide

Methylene Chloride

_{Good Practice} 

or when used for radioisotope work. In this instance, the fume hood exhaust treatment system must be approved by the SU Radiation Safety Officer prior to installation and use.

7.  Laboratory ventilation exhaust fans shall be spark-proof and constructed of materials or coated with corrosion resistant materials for the chemicals being transported. V-belt drives shall be conductive.

_{NFPA 45}

8.  Vibration isolators shall be used to mount fans. Flexible connection sections to ductwork, such as neoprene coated glass fiber cloth, shall be used between the fan and its intake duct when such material is compatible with hood chemical use factors.

_{Good Practice per Stanford University} 

9.  Each exhaust fan assembly shall be individually matched (cfm, static pressure, brake horsepower, etc.) to each laboratory ventilation system.

_{Industrial Ventilation Manual} 

10.  Exhaust fans shall be located outside the building at the point of final discharge. Each fan shall be the last element of the system so that the ductwork through the building is under negative pressure.

_{8 CCR 5154.1(e)(6)}

_{ANSI/AIHA Z9.5,}

An exhaust fan located other than at the final discharge point can pressurize the duct with contaminated air. Fume hood ducts must be maintained under negative pressure.

11.  Fans shall be installed so they are readily accessible for maintenance and inspection without entering the plenum. If exhaust fans are located inside a penthouse, PPE needs for maintenance workers shall be considered.

_{NFPA 45}