Chemical Fume Hoods

Chemical fume hoods are intended to remove vapors, gases and dusts of toxic, flammable, corrosive or otherwise dangerous materials. They are one of the most important engineering controls in a lab. If you have reason to believe that a fume hood in your lab is not functioning properly, please call (392-1591) or email jramsey@ehs.ufl.edu (on-campus laboratories) to set an appointment for a hood profile. If it is an obvious malfunction, see Fume Hood Repairs. If your lab is located off-campus please contact your building maintenance staff.

Chemical Fume Hood Profile

Types of Chemical Fume Hoods

Fume Hood Materials and Design

Fume Hood Operating Guidelines

Fume Hood Repairs

Fume Hood Safety Instructions for posting on hoods

Chemical Fume Hood Profile

Chemical fume hoods utilized by the University of Florida students, faculty and staff are profiled annually by EH&S trained staff. The reason for certification is two fold: first, to assure that hoods are functioning within specifications to protect the workers using them; and second, to comply with fire codes. Fume hoods are normally profiled during the annual laboratory safety survey. If there is concern that the hood is not functioning properly or if the certification date on the EH&S fume hood profile sticker is more than a year old call Laboratory Safety (392-1591) to have the hood re-profiled.

Types of Chemical Fume Hoods

The following is a brief description of the types of fume hoods in UF laboratories:

Full Sash - Face velocity increases as sash is lowered and decreases as sash is raised. Therefore lab staff can regulate airflow. For the hood to have the required airflow it is imperative that the lab staff follows sash heights documented on the profile sticker.

A small bypass chamber above the sash provides airflow through the hood when the sash is down. Most hoods have an airfoil across the bottom and this also provides airflow across the floor of the hood when the sash is fully closed.

Bypass hood - A bypass opening above the sash and the airfoil provides relatively constant face velocity regardless of sash position. The EH&S profile sticker will have a slash mark through the lines where sash height positions should be.

Walk-in hood - Designed so that lab personnel can walk into the hood to set up large and bulky equipment. (It is not intended that personnel stay in the hood when equipment is operating.) Profile sticker sash height settings must be followed when using this type of hood.

Auxiliary Air hood - This may be either a full sash of bypass hood where a percentage of the air to be exhausted comes from a source other than the room (usually outside air). The auxiliary air is directed from a grille above the workers head and in front of the hood sash. This air flows down the front of the sash and is captured through the sash opening. The engineering design of this type of hood is to reduce the amount of conditioned air (either cooled or heated air) to be exhausted from the room through the hood.

Perchloric acid hood - This may be either a full sash of bypass hood with a wash down system in the hood's baffles and duct work to prevent or wash away build up of explosive perchlorate crystals in the duct work. Perchloric acid hood have dedicated ducting and motor (ductwork is not manifolded with other fume hoods). Profile sticker sash height settings must be followed when using this type of hood.

Radioisotope hood - Some radioisotope work requires a dedicated ducting and motor (which is not manifolded to other fume hood ducting). The interior of the hood is rolled stainless steel so there are no joints or cracks and any spills are contained within the hood. Profile sticker sash height settings must be followed when using this type of hood.

Fume Hood Materials and Design

Sash Glass - This is made of multi-paned safety glass. It will withstand impacts and small explosions by "spidering" but not shattering.

Interior Linings - This is made from a number of different types of materials, depending on designed use. Radioactive use hoods are usually made of rolled and seamless stainless steel. Chemical use hoods are made of chemical resistant materials. Some older hoods on campus have a transite liner. This material contains asbestos. This transite liner is safe for use but must not be drilled, broken or removed by lab staff. If there are any concerns about the hood lining, please contact EH&S Laboratory Safety at 392-1591.

Ductwork - Chemically compatible duct has been installed for all hoods when the hood was installed or the building was built. It is understood that over time, the lab's functions and focus changes, which may mean different chemicals are being used than the original designed use. If there is any concern about the use of chemicals in the hood and their compatibility with the hood and duct materials, please contact EH&S Laboratory Safety at 392-1591 to have the hood and duct materials assessed.

Sash Counterweight System- These are designed to aid in the movement of the sash. Lead or steel weights are attached by cables to the sash to counter the weight of the sash. If these break, please see Fume Hood Repairs to have these repaired.

Utilities- Air, gas, water, vacuum, etc. may be supplied to the hood for lab staff use. If these need to be repaired, do not attempt to repair or alter these utility hook-ups. Please contact the appropriate PPD unit (Fume Hood Repairs) to have them repaired.

AirFlow Monitors- These alarm units are required for all new or renovated hoods and labs. These monitor airflow and will alarm (both audibly and visually) when airflow falls below a safe setting. This reduced airflow will not have the capture velocity to collect and remove chemical vapors. These may flow out of the hood and be hazardous to staff. Older hoods are not required to have these monitors, but they may be installed at the lab's expense. Please contact EH&S Laboratory Safety (392-1591) for information on inexpensive airflow alarms to retrofit onto hoods.

Hood Exhaust Systems- Hood exhaust systems are different from building to building. Some exhaust systems are manifolded so that numerous fume hoods and room exhausts are tied together and exhausted collectively. These systems must run continually and lab staff has no control over the system. Older hoods and buildings may have hoods that may be turned off when not in use. This will save conditioned air, but may reduce the lab's capacity to remove vapors generated in the lab. Lab staff will need to decide if it may be advantageous to have the hood working while the lab is occupied.

Fume Hood Operating Guidelines

To maximize hood effectiveness and minimize personal exposure to toxic vapors or gases, use fume hoods in accordance with these operational guidelines:

Operate the hood at the proper sash height, as indicted on the EH&S profile sticker located on the front of the hood. For variable air volume or bypass hoods sash heights will not be posted. These hoods should maintain the velocity (indicated on the label) at any sash height, but sashes should be lowered to a position where they can provide additional protection from splashes, sprays, and fires. Minimize release of contaminants into the work area by reducing pedestrian traffic in front of hoods, particularly during hazardous experiments. Also minimize nearby disturbances, such as doors opening or closing, people walking by, and any quick motion in order to prevent cross drafts. Do not position fans or air conditioners so as to direct airflow across the face of the hood. This can interfere with airflow and containment of hazardous chemicals.

• Do not block airfoil: Many labs place absorbent paper on the floor of the hood and over the airfoil to catch spills. The airfoil provides airflow across the floor of the hood, especially when the sash is closed. If you use absorbent paper in the hood, please do not block the airfoil.
• Side panels must not be removed. Doing so will interfere with airflow and containment, as air will be brought into the hood from these openings. It is dangerous to use the hood in this condition. If side panels are found missing, EH&S will remove the hood from service until they are installed.
• Place bulky equipment away from sidewalls to allow airflow around the equipment.
• Place any bulky equipment towards the rear of the hood and raise it about 2 inches off the surface with blocks or bricks. This will allow airflow around and under the equipment. Equipment placed near the hood face will cause great variation in airflow. This equipment must be moved towards the rear of the hood, but do not place this equipment against the rear wall of the hood, as it will block airflow to the rear baffles. The use of riser blocks will prevent obstruction of back exhaust slots.
• Work as far inside the hood as possible, at least 4 to 6 inches from the front edge with the sash face between you and task at hand. All equipment should be a minimum of 9-12 inches away from the hood face.
• Keep sash face clean and clear. To encourage use of sash as added protection against splashes, sprays, etc. keep sash face clean. If sash face must be blocked with paper for certain experiments, please take it down after the experiment is complete.
• Do not use the hood as a storage cabinet for chemicals or equipment. Materials stored in fume hoods should be kept to a minimum and stored in a manner that will not interfere with airflow. This can be accomplished by equipping the hood with perforated shelves on the side walls and/or allowing at least 3 inch spaces between containers or equipment so air can flow around them to the back exhaust slot.
• Place any heat-generating equipment in the rear of the hood. Heating devices in the hood produce convection currents that can disrupt airflow.
• Do not use a hood for any function it was not designed for, such as perchloric acid, radioisotopes, etc. The generation of perchloric acid vapors requires specially designed fume hoods with wash-down systems. Failure to use a wash-down system will result in the deposit of explosive perchloric acid crystals that may detonate in the hood ductwork. Hoods used for radioisotopes must be approved by Radiation Control.
• Wear protective equipment! Fume hoods do not prevent accidents or chemical splashes. Personnel protective equipment (safety glasses, gloves, aprons, etc.) appropriate to the conditions must always be worn.
• Close sash when finished with hood work or when leaving experiments or chemicals unattended! This simple procedure has contained many fires and explosions within a hood.

Fume Hood Repairs

Staff or PI should initiate repairs to a fume hood if:

• EH&S determines that a fume hood is not functioning properly and requires adjustment or repairs
• Obvious repairs are necessary (light bulb replacement, leaks from sink or duct work, loud or unusual noises from motor or fan, etc.)
• Reduced or no air flow or when hood monitor or alarm indicates no airflow. If you do not have a monitor, a simple test is to place a tissue above the opening of the hood. Initiate repairs if the tissue does not draw towards the back of the hood.

The following procedures should be implemented to ensure that repairs are completed in a safe and timely fashion.

• Hoods located in IFAS Buildings
• Hoods located in the Health Center
• Hoods located in all other campus buildings serviced by PPD
• Hoods located in non-IFAS off campus buildings please contact your building maintenance staff.

IFAS Buildings

1. Contact IFAS Facilities Services (392-1984) to arrange for the necessary repairs and request the work order number for tracking purposes.
2. Clean out all chemicals, equipment, etc. from inside the hood.
3. Once repairs are completed by IFAS Facilities Services, contact EH&S Laboratory Safety (392-1591) to arrange for final hood profile.

Health Center

1. Contact Health Center Physical Plant (392-4411) to arrange for the necessary repairs and request the work order number for tracking purposes.
2. Call EH&S Laboratory Safety (392-1591) for clearance. You will need the work order number.
3. Clean out all chemicals, equipment, etc. from inside the hood.
4. Once repairs are completed, contact EH&S Laboratory Safety (392-1591) to arrange for final hood profile.

Other campus buildings

1. Contact Work Management Center (392-1121) to arrange for the necessary repairs and request the work order number for tracking purposes.
2. Call EH&S Laboratory Safety (392-1591) for clearance. You will need the work order number.
3. Clean out all chemicals, equipment, etc. from inside the hood.
4. Once repairs are completed by PPD, contact EH&S Laboratory Safety (392-1591) to arrange for final hood profile.