Top 5 Commonly Asked Questions When Buying a New Fume Hood

Hey folks!

Admit it, buying a new fume hood is not an easy task. It requires lots and lots of research since it involves a huge amount of money. Just like buying a new car, you bid your time to get to know the product first before you give your big YES.

Listed below are the most commonly asked questions most buyers asked before they buy a new hood.

How definite are you that you really need a fume hood? There are different enclosures available and a lot of these looks similar but functionality wise, nah, they're different. I've already tackled this on a separate blog so you might want to check it out first, then come back here later.

Photo below will summarize. A fume hood only provides operator protection from hazardous and toxic chemicals. A laminar flow offers sample protection but not for the operator. Biosafety cabinets offer protection for both the user and the samples, however, it cannot function what a typical fume hood does!

If you're certain that you need a fume hood, then you have to identify whether you need a general purpose fume hood or a specialized one. For a more detailed discussion on the different hoods available, click this link. Enumerated below is a quick summary:

• General Purpose Fume Hood - used for applications that involves the ff: dilution, mixing of acids, slight (mild) evaporation, precipitation reaction, extraction, sample preparation, titration, filtration,e tc.
• Specialized Hoods
• Acid Digestion - for applications that involve using acids such as hydrcohloric, sulphuricm phosphoric and nitric.
• Perchloric Hood - if application involves using perchloric acid. Has a wash-down system to clean up the surface from any perchloric salts.
• Radioisotope hoods - for applications that involve radioactive materials such as alpha and beta particles
• Floor-mounted fume hood - provides comfortable space when users have to deal with large apparatus and hazardous containers

It pays to know. Again, be definite with what you need. It's surprising how many different fume hood exists, so you better be sure you select the right fume hood for your needs. If in doubt, reach out to your distributor or to a company's product expert/ specialist to confirm the right fume hood for your intended application.

Good question! First, what's the difference? A ducted fume hood requires complex ducting system to vent out air towards the atmosphere. Otherwise, a ductless hood recirculates air back to the laboratory, hence, no need for an expensive ducting system.

Having the liberty to choose between the two often causes confusion among laboratory planners. Worry not, listed below are important points to consider when choosing between a ductless or a ducted fume hood.

Important Points to Consider:

a.  Do you have an existing ducting system? If yes, then you might want to use a ducted fume hood. If outside ventilation is not possible, then go ductless!

b. Do you intend to heat solvents/ reagents/ acids inside the hood? If yes, then a ducted fume hood is more suitable. A ductless fume hood uses carbon filters to filter contaminated air. If force evaporation is involved, it will shorten the life of the carbon filter. Practicality wise, it's better to have a ducted hood.

c. Does your application involves using lots of chemicals? If yes, preferably a ducted fume hood is a better option. Carbon filters for ductless fume hoods are impregnated to absorb a specific group of chemicals only. Hence, choosing a ductless hood will only limit you to a list of chemicals approved by your distributor/ fume hood provider.

Depending on your budget, there's a list of features you would probably want your hood to have. Here's a few to name:

 

Source: Photo courtesy of Esco

• Airflow Monitoring Device/ microprocessor controller - an airflow monitoring device provides an alarm if the hood's face velocity falls below the recommended range. It will also alarm if it goes higher than the set range. A too high face velocity causes air turbulence inside the hood and you wouldn't want that to happen since it would mean there's a tendency for contaminated air to leak out towards the operator.
• Worktop - choosing the wrong worktop spells disaster. A stainless steel worktop is suitable for perchloric acid applications but no longer the perfect choice if in addition to perchloric acid, if it would also entail the usage of both hydrochloric and nitric. 
• Auto-sash sensor/ motorized sash - with the cost of electricity not going down, what better way to save energy is to have a sensor that automatically closes the sash once it detects that nobody is working in front of the hood. 
• Circuit Protection Board - this serves to protect the fume hood unit whenever there are sudden fluctuation of current.

 

 Figuring out where to locate the hood inside the laboratory is sometimes painstakingly the most difficult. Location impacts the nature and extent of external airflow disturbances, which may affect fume hood's performance. 

When installing the hood, it should be located as far away as possible from sources of airflow disturbance and in an orientation which optimally shields the hood's airflow from all external airflow disturbances. Any of the following will cause airflow disturbance:

• Opening of a door
• A person walking by or if located near any pedestrian traffic routes, thoroughfares or walkways
• or placing near an air-conditioning unit

 Position requirements should be discussed thoroughly with your supplier when in doubt. 

There are numerous other things you can add to your fume hood to ensure a safe and reliable performance. If you're using a ducted fume hood and if you're heavy on the use of acids, you might consider buying a wet scrubber. A scrubber works like a neutralizer -- it neutralizes the fume generated before it leaves the exhaust system. It helps save the environment and reduces air pollution.

 

 Source: Photo courtesy of Esco

If you are using a ductless fume hood, you might want to consider buying a Volatile Organic Compound (VOC) sensor. What it does is that it helps you monitor if your carbon filters are already scheduled to be change. Extra cost but it's worth the buck if it let you know this important information of knowing.