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NFPA 45 and the ASPS

NFPA-45 - 2000 Edition*

NFPA45-6.4.6 Laboratory hood face velocities and exhaust volumes shall be sufficient to contain contaminants generated within the hood and exhaust them outside of the laboratory building. The hood shall provide containment of the possible hazards and protection for personnel at all times when chemicals are present in the hood.

NFPA45-A6.4.6 - Laboratory fume hood containment can be evaluated using the procedures contained in ASHRAE 110, Method of Testing Performance of Laboratory Fume Hoods. Face velocities of 0.4 m/sec to 0.6 m/sec (80 ft/min to 120 ft/min) generally provide containment if the hood location requirements and laboratory ventilation criteria of this standard are met.

In addition to maintaining proper fume hood face velocity, fume hoods that reduce the exhaust volume as the sash opening is reduced should maintain a minimum exhaust volume to ensure that contaminants are diluted and exhausted from a hood. The hood exhaust airflow should not be reduced to less than 127 L/sec/m2 (25 cu. ft /min/ft2) of internal hood work surface even when the sash is fully closed.

When using fume hoods the face velocity is typically controlled at 100 fpm over the travel of the sash for open sash containment. When the hood is fully closed a minimum 25 CFM/ sq. ft. of work surface (or 50 CFM/ft of sash for a 24-inch deep work surface) is required. The minimum airflow equates to about 20% of the maximum airflow when the fume hood sash is fully open. This minimum ensures that when the fume hood sash is closed the fumes do not build up inside the hood.

NFPA 45-6.8.3 - Laboratory Hood Sash Closure. Laboratory hood sashes shall be kept closed whenever possible. When a fume hood is unattended, its sash shall remain fully closed.

NFPA 45-A.6.8.3 - Users should be instructed and periodically reminded not to open sashes rapidly and to allow hood sashes to be open only when needed and only as much as necessary.

Typically, during the day, fume hoods are only attended 5% of the working hours yet left open 100% of the time. This 5% equates to less than 30 minutes a day that a person needs to have there hands inside a fume hood. For this reason the New-Tech Automatic Sash Positioning System™ (ASPS™) was developed to improve safety and save energy.

Note that face velocity set back approaches have been employed to reduce the 100 fpm to 60 fpm (a 40% reduction in airflow) when the fume hood is unattended. However, this reduction cannot reduce the minimum airflow of 50 CFM/ft of sash when the hood is closed. Therefore, the only time the setback is functional, the sash is open and unattended, which is contrary to NFPA 45 6.8.3.

The New-Tech ASPS™ closes the fume hood sash when the fume hood is unattended thus the minimum airflow of 50 CFM/ft is achieved with any VAV fume hood airflow control system (a 80% reduction in airflow). Ensuring that the fume hood sash is closed when the fume hood is unattended complies with NFPA-45 6.8.3, provides maximum containment and energy savings.

The ASPS™ complies with the NFPA 45 6.8.3 code without the need for periodically reminding and instructing the users of fume hoods to shut the sash. The ASPS also opens the fume hood sash and controls the opening and closing speed to optimize containment.

* Copyright © 2000 Edition, National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02269-9101 USA

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