Why Fume Hood Performance Audits Are Important

May 4, 2016

 

Fume hoods are used in various applications ranging from research and development, both at an industrial as well as at an educational level such as university and college science laboratories, to government material testing facilities.

 

Generally, chemical and biological experiments are performed within a fume hood and may involve a wide variety of chemical agents that can produce toxic, noxious, or even fatal effects in close proximity. With regards to typical university research laboratories for example, many corrosive or poisonous gases can result in the fume hood from the work performed, which is why safety should be a number one concern for these applications.

 

Specifically, the ability for a fume hood to contain and exhaust these gases and particles within it determines a fume hood’s level of functionality and performance. As seen in the ASHRAE Z9.5 guidelines with regards to laboratory environments, a fume hood must be able to suck in air at the sash opening at approximately 100 fpm during occupied conditions.

 

This means that when the fume hood is being occupied by gases or chemicals within its confined space and there is an operator standing in front of the fume hood sash, the exhaust must be operating at a speed such that the chemicals or gases in the hood do not overflow or flow out of the fume hood sash opening and into the direct breathing space of the operator. Usually, the sash acts as a barrier between what is contained in the fume hood and the breathing space however this is dependent on how far open the sash is and at what velocity the gases are being exhausted. This is why speed of response is critical for laboratory or fume hood applications specifically.

 

Belnor Engineering Inc. provides the controls needed to achieve this through the Phoenix Controls product line. We offer a range of specialized exhaust and supply valves, controllers, and even usage-based devices that can decrease the overall energy consumption of a lab space. By using adequately sized venturi valves for the fume hood and general exhausts, we are able to provide a fast-acting 1- second response time between the sash sensor, which dictates how open the sash is by measuring the vertical displacement and providing a signal to the fume hood exhaust valve controller, and the fume hood controller.

 

This signal causes the controller to adjust the spring-cone assembly within the valve to provide the desired flow set point and face velocity at the sash. If there is a slow acting response time between the sash sensor and the fume hood controller, the contained gases and chemicals would not be exhausted fast enough to achieve the 100 fpm ASHRAE requirement. During unoccupied hours, ASHRAE suggests that the face velocity at the hood opening can fall to 60fpm however if a slow acting response system is in place, such as VAV boxes, for example, then the velocity can fall even lower and the fume hoods can lose containment, which can go beyond the breathing space of an operator and into adjacent corridors and the rest of the building. In most sensitive applications, a spill like this would require decontamination and severe down-time.

 

Belnor Engineering Inc. offers fume hood performance audit services, which aim at determining the containment characteristics of the hood in everyday conditions. Once the fume hood has been confirmed to be in working order, we will go ahead with ASHRAE 110-1995 fume hood test operation procedures which include the Flow Visualization (smoke pencil test) as well as a measurement of the face velocity using an air data multimeter. Following these tests, our site technician would provide a complete report outlining the issues or problems with the system, if any, as well as recommendations to the fume hoods and graphical results of the measurements taken.

 

We currently have contracts with universities, colleges, research facilities and laboratories all across Ontario and have performed these services across the country. It is important to note that performance of fume hoods can deteriorate over time, which is why we encourage annual inspections and verifications of the laboratory space in order to ensure adequate safety as per the widely-adopted ASHRAE guidelines and requirements. All in all, the main safety characteristic of the fume hood is its containment abilities, therefore we highly recommend using VAV systems for a laboratory environment as well as ensuring fume hood exhaust at the specified velocity.

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