Questions and Answers on... Fume Hoods

You need a fume hood... now what?

The purpose of a fume hood is to contain contaminants and prevent their escape into the laboratory. This is accomplished by drawing contaminates within the hood’s work area away from the user, so that inhalation and contact are minimized. Here are a few commonly asked questions about fume hood systems.

1: Where should the hood be placed in the lab?
Whether adding one or 100 fume hoods to a laboratory, planning is critical. Each hood is affected by the room’s ventilation and traffic flow. When selecting a fume hood location, operator convenience, work flow, and exhaust duct locations should all be considered. It is both inconvenient and dangerous to install a fume hood so that the operator is forced to work in the line of traffic movement. The presence of cross drafts will adversely affect the performance of the fume hood so it is a good idea not to locate the fume hood near open doors and windows.

2: Do I need an explosion-proof fume hood?
Don’t believe that any fume hood is truly explosion proof. As a common practice, manufacturers use that term to mean they have modified their standard hood to help eliminate the likelihood of explosions. Such modifications include eliminating electrical switches and moving outlets away from the fume hood cavity. Other changes can include retrofitting the hood with an explosion-proof remote blower.

3: Do I need a specialty hood?
You may want to consider a specialty hood type if you are using  radioactive, explosive, extremely corrosive, or toxic materials in your lab processes. ADA hoods address the specific needs of wheelchair operators and walk-in hoods will accommodate large apparatus or complex set-ups.

4: What about a fume hood alarm?
Hood alarms should be considered with any fume hood system. An alarm will notify the user immediately of a malfunction in the exhaust system. Alarms are required when medium to heavy use of solvents and acids are present and any use of chemicals that could produce a volatile condition.

5: Is a fire extinguisher really necessary?
You may want to consider a fire extinguisher if you are operating your system with potentially dangerous applications that could produce a fire in your hood cavity. Some manufacturers offer automatic fire extinguishers that mount inside or adjacent to the hood and discharge at predetermined temperature set points. Fume hoods that are 72” and wider require the use of two fire extinguishers for adequate protection.

6. Do I need a filter or scrubber?
Depending on the hazard level associated with your laboratory operation, as well as the degree of pollution abatement required, treatment for your system’s effluents may be necessary. Types of treatment include charcoal, HEPA filters, and wet scrubbers.

7: What is an add air hood?
The add air hood is also known as an auxiliary air, make-up air, induced air, or balanced air. The add air hood was initially seen as a simple and dramatic way to conserve energy and reduce energy costs since the hood provides up to 70% of the hood exhaust requirements. With a bypass similar to the bypass hood, outside air is introduced through the add air plenum, thus minimizing the amount of conditioned room air required. Caution should be used when considering this type of hood due to the balancing of the air coming in from the outside.

8: What is a low-flow hood?
The low-flow hood operates with a simple constant volume operation offering “zero risk” energy savings that is not dependent on the operator. Clean room air flows into the operator breathing zone and eliminates potential hazards from fumes, vapors, and particles. The configuration increases net usable space versus gross space and decreases duct chase sizes, floor to floor clearances, mechanical space, and roof loads.

Questions 9-20 are available in the article: More Questions and Answers on Fume Hoods

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