Fume Hood
A fume hood is a necessary part of any laboratory that deals with toxic fumes and/or chemicals. A fume hood (also known as a chemical fume hood, fume closet, or fume cupboard) is a piece of equipment designed to keep lab personnel safe by capturing airborne pollutants and directing them away from the user.
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Types of Fume Hoods
Ductless Fume Hoods
A ductless fume hood relies on a carbon filter to remove toxic fumes from the workspace. Also, it’s a more eco-friendly version of the fume hood. Rather than directing the fumes outside of the building, the carbon filter removes the chemicals from the air and redirects it back into the lab. Industry experts consider ductless fume hoods the most energy and cost-efficient.
Chemical Fume Hood
These are for labs that regularly handle dangerous chemicals. They feature the clear sash so that workers can have a complete view of the substances they’re working with without coming into direct contact with them.
ADA Fume Hoods
Manufacturers engineer these to comply with the A.D.A. (Americans with Disabilities Act) standards to ensure any employee can have access to and operate it.
Canopy Fume Hood
Interestingly, you won’t find these hoods exclusively in labs. They are ventilation systems in use in many professional kitchens, as well. For instance, you can always locate them directly above stoves or ovens. Using a fan, they remove excessive heat or steam from the work area.
Perchloric Acid Fume Hood
This fume hood is exclusively for labs working with perchloric acid. The essential function is to prevent the formation of perchloric salt. They use a specific grade of steel to prevent any damage from the acid and maintain sterile conditions.
Variable Air Fume Hood
A variable air fume hood is a device with a greater deal of control over the air which the unit exhausts. They feature luminous, ultra-modern interior lighting systems. And, they’re generally more cost-efficient.
Walk-In Fume Hoods
These fume hoods are generally used in labs that handle larger materials. Since fumes are filtered out, workers can handle substances with harmful vapors while standing in the unit.
A fume hood is a ventilated enclosure in which gases, vapors and fumes are captured and removed from the work area. An exhaust fan situated on the top of the laboratory building pulls air and airborne contaminants through connected ductwork and exhausts them to the atmosphere.
The typical fume hood found in Princeton University laboratories is equipped with a movable front sash and an interior baffle. Depending on its design, the sash may move vertically, horizontally or a combination of the two and provides some protection to the hood user by acting as a barrier between the worker and the experiment.
The slots and baffles within the hood direct the air and, in many hoods, can be adjusted to allow the most even flow. It is important to prevent the baffles from becoming blocked, by excessive material storage or equipment, since this significantly affects the exhaust path within the hood and as a result, the efficiency of hood capture.
The beveled frame around the hood face, called the airfoil, allows for even air flow into the hood by eliminating sharp curves to reduce turbulence.
Constant volume – where the exhaust flowrate or quantity of air pulled through the hood is constant. In this configuration, when the sash is lowered and the cross-sectional area of the hood opening decreases, the velocity of airflow (face velocity) through the hood increases proportionally. Thus, the velocity of air at the hood face is increased with the lowering of the sash.
Variable air volume (VAV) - where the exhaust flowrate or quantity of air pulled through the hood varies as the sash is raised or lowered in order to maintain a constant face velocity. Therefore, when the sash is lowered and the cross-sectional area of the hood opening decreases, the velocity of air flow (face velocity) through the hood remains constant, reducing the total air volume exhausted.
Parts Of The Fume Hood
Hood body: This is the part of the fume hood that is clearly visible and serves to trap hazardous fumes.
Fume hood sash: The sash is the adjustable portion of the front opening that users can raise or lower to access the interior workspace. Every fume hood will state the optimal configuration required for properly containing the chemicals. For the fume hood to work efficiently, it is important to follow the sash guidelines. When not in use, the sash should be closed. A fume hood is not meant for storage, so remember to remove all chemicals before closing the sash.
Baffles: Baffles are movable partitions. They are used to create slotted openings along the back of the hood to equally direct the air that is being exhausted out. When adjusted properly, baffles will eliminate any dead spots and optimize the efficiency of the fume hood in capturing the contaminated air.
Work surface: The work surface is the area below the hood where the laboratory work is performed. This could be a bench top or alternatively, the floor of a walk-in fume hood.
Airfoil: The airfoil is located along the bottom and side edges of the fume hood. Airfoils help to simplify the airflow and prevent whirls of air known as eddies from carrying contaminants out of the hood and into the work area. There is also an open space below the bottom airfoil that works as a place for the hood to exhaust when the sash is completely closed.
Face: The face of the fume hood is the plane that exists between the bottom of the sash to the work surface. The hood pulls air from the laboratory into the fume hood through this opening. It also serves as the entry point to the work area. This is where face velocity is measured.
Exhaust plenum: The exhaust plenum helps to equalize airflow across the fume hood face.
How To Work Safely With Fume Hoods
Always use a fume hood for applications, experiments, and procedures where chemicals are handled. In cases of spillage, explosion or fire, a fume hood can temporarily serve as shield and containment. Ensure that the fume hood is durable and compatible with your application.
Do not use a fume hood for handling pathogens or biological samples. Fume hoods are not designed to handle biohazards, they do not provide sample protection and are not suitable for UV decontamination.
Minimize external airflow disturbances. Fume hood must be placed away from foot traffic, windows, and doors. External airflow may cause turbulence and affect containment. Also, fume hoods are advised to be placed side by side rather than facing each other.
Know and check your airflow! For fume hoods, air always goes into the hood, away from the operator and upwards through the carbon filters or directly into the ducting. As per ASHRAE 110-2016 a properly working fume hood should have a face velocity between 0.3-0.6 m/s at proper sash height level. For ducted fume hoods, ensure that the exhaust system has been turned on before starting work.
Mind the sash. When working, keep the sash at the recommended height level. Only go beyond the maximum opening when loading tall apparatus. Remember that the lower the sash, the safer you are. If the fume hood is not operational, make sure to fully close the sash. In cases of power outage, and active alarms, immediately cease experiment, and then close the sash.
Wipe chemical spills immediately. Avoid cleaning spills with incompatible solvents as this may result in worktop deterioration. Do not use bleach to clean stains as this may damage the fume hood unit further.
Declutter and keep things organized. A Fume hood should not be used for chemical storage. Do not keep reagent bottles, beakers, flasks, and test tubes in the work area. Storing chemicals and overcrowding will cause airflow disruption and will affect containment. Only place the reagents and equipment that you need for the current procedure. Always keep your work area clean to prevent accidents and contamination.
Dispose of chemical waste properly. Do not at all cause, throw chemicals into the hood's sink or let it evaporate as a form of disposal. Chemicals should be properly placed in their respective waste bottles and must be disposed of according to the facility’s guidelines.
Perform routine maintenance and certification! To help your fume hood last longer and to ensure superior fume containment, have it checked once a year. Proper maintenance procedures should include face velocity and smoke visualization tests. It is a fume hood's job to remove the risk of chemical exposure but it's our responsibility to have it maintained.
Installation & Maintenance Of Fume Hood
Proper Hood Placement
The location of the fume hood within the laboratory should be carefully chosen to optimize airflow patterns and minimize potential interferences. It should also allow for easy access and operation.
Connection to Exhaust System & Ductwork
For ducted fume hoods, the connection to the external exhaust system and ductwork must be expertly configured to ensure the efficient removal of contaminants. Proper sealing and airflow balancing are crucial aspects of this installation process.
Periodic Inspections & Testing
Regular inspections and testing of the fume hood are essential to promptly identify and address any potential issues. This includes checking for leaks, verifying airflow, and ensuring safety features function correctly.
Maintenance Best Practices
Following manufacturer-recommended maintenance schedules and practices is essential for prolonging the lifespan of the fume hood and preserving its safety features. This may include filter replacements, sash repairs, and airflow adjustments.
Efficiency Of Fume Hood
The efficiency of a fume hood is measured by its hood face velocity and required air flow.
Hood face velocity is a measurement of air flow speed across the imaginary plane running between the bottom of the sash to the work surface. Generally measured in feet per minute (fpm), the greater the hood face velocity, the more quickly toxins and other vapors can be flushed from the system.
Required airflow is related to hood face velocity in that it is a measurement of the amount of air flow required to achieve a laminar flow velocity of 100 feet per minute.
General purpose fume hoods usually function with a hood face velocity of 100 fpm. Stronger fume hoods are available to work with specific chemicals and technologies. Two commonly sought-out types include radioisotope and perchloric acid hoods.
Radioisotope hood systems are ideally made from welded stainless steel to ensure against absorption of radioactive materials. In order to comply with licensing requirements, radioisotope hoods require a face velocity of 125 fpm.
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FAQ
Q: What is the purpose of a fume hood?
Q: When should I use a fume hood?
Q: How safe is a fume hood?
Q: What should you do immediately before using a fume hood?
Before using a fume hood, make sure your work area is clean and uncluttered.
Never use the fume hood to store chemicals and equipment between procedures.
Verify the date on the inspection sticker on the fume hood. ...
The fume hood average face velocity should be between 80-150 feet per minute.
Q: What precautions should be taken during fume hood?
Q: What is the life expectancy of a fume hood?
Q: What should be checked prior to using a fume hood?
Q: What to do if you don't have a fume hood?
Q: How often should you clean a fume hood?
Typical ducted fume hoods used for the same process with low-risk chemicals can go months without a deep clean. Specialized fume hoods used for dangerous or varied processes and chemicals may require cleaning after every use.
Q: How do you disinfect a fume hood?
Q: What should you check for before using a fume hood?
Ensure users are properly trained.
Know the chemicals.
Ensure sash is opened to proper height.
Check the air gauge.
Ensure exhaust fan is working.
Keep spark sources away.
Check the air filters.
Q: What rules should be followed to properly use a fume hood?
Q: How safe are fume hoods?
Q: Why would someone use a fume hood?
Q: What precautions should be taken during fume hood?
Q: How long does a fume hood last?
Q: What should be checked prior to using a fume hood?
Q: When would you be required to use a fume hood?
Q: What is the main reason for using a fume hood?
Q: How to properly use a fume hood?
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stainless steel fume hood