1.  Chemical fume hood exhaust fans should be connected to an emergency power system in the event of a power failure.

Good Practice per Stanford University EH&S

This backup power source will ensure that chemicals continue to be exhausted. EH&S recognizes that it may not be practical to provide emergency power sufficient to maintain fume hood functioning at normal levels but recommends an emergency supply of at least half of the normal airflow.

2.  Emergency power circuits should be available for fan service so that fans will automatically restart upon restoration after a power outage and supply at least half of the normal airflow. 

Good Practice per Stanford University EH&S 

Continual fan service will ensure that hazardous materials are exhausted continually.

3.  Momentary or extended losses of power shall not change or affect any of the control system’s setpoints, calibration settings, or emergency status. After power returns, the system shall continue operation, exactly as before, without the need for any manual intervention. Alarms shall require manual reset, should they indicate a potentially hazardous condition.

4.  Fume hood ventilating controls should be arranged so that shutting off the ventilation of one fume hood will not reduce the exhaust capacity or create an imbalance between exhaust and supply for any other hood connected to the same system.

NFPA 99, Chapter 5-4.3.4

5.  In installations where services and controls are within the hood, additional electrical disconnects shall be located within 15m (50ft) of the hood and shall be accessible and clearly marked. (Exception: If electrical receptacles are located external to the hood, no additional electrical disconnect shall be required).

NFPA 45, Chapter 6-8.4.1

Locating services, controls, and electrical fixtures external to the hood minimizes the potential hazards of corrosion and arcing.

6.  Hood lighting shall be provided by UL-listed fixtures external to the hood or, if located within the hood interior, the fixtures shall meet the requirements of NFPA 70, (National Electrical Code).

NFPA 45, Chapter 3-6

7.  Light fixtures should be of the fluorescent type, and replaceable from outside the hood. Light fixtures must be displaced or covered by a transparent impact resistant vapor tight shield to prevent vapor contact.

Good Practice per Stanford University EH&S

Fluorescent bulbs radiate less heat than conventional bulbs while maintaining a safe and illuminated work area inside the hood.

8.  The valves, electrical outlets and switches for utilities serving hoods should be placed at readily accessible locations outside the hood. All shutoff valves should be clearly labeled. Plumbing (e.g., vacuum lines) should exit the sides of the fume hood and not the bench top.

NFPA 45, Chapter 6-8.5.1

NFPA 99, Chapter 5-4.3.6 (Health Care) 

Good Practice per Stanford University