The requirements of this Guide apply to all UNC laboratory buildings, laboratory units, and laboratory work areas in which hazardous materials are used, handled, or stored.
Fume hoods should not be located adjacent to a single means of access to an exit. Recommend that hoods be located more than 10 feet from any door or doorway.
Fume hoods must not have large equipment located in front.
Hoods should not be located in room corners, near windows or near very cold equipment.
Fume hood openings should not be located opposite workstations where personnel will spend much of their working day, such as desks or microscope benches.
Fume hoods should not face each other across narrow aisles.
An emergency eyewash/shower station shall be within 10 seconds of each fume hood.
Per 8 CCR 5162, the requirement for an eyewash/shower is triggered when an employee may be exposed to substances, which are “corrosive or severely irritating to the skin or which are toxic by skin absorption” during normal operations or foreseeable emergencies. Fume hoods are assumed to contain such substances; hence, UNC interprets this regulation to mean that emergency eyewash/shower station shall be within 10 seconds of fume hoods.
An ADA emergency eyewash/shower shall be within 10 seconds of an ADA fume hood (minimally one ADA hood per laboratory floor).
The location of at least one ADA hood per floor will enable disabled individuals to conduct their research without having to transport chemicals, etc. in elevators.
Consider the following factors when selecting a fume hood:
- Room size (length x width x height)
- Number of room air changes
- Lab heat load
- Types of materials used
- Linear feet of hood needed based on
- Number of users/hood
- Frequency of use
- % of time working at hood
- Size of apparatus to be used in hood, etc.
Constant Volume Hoods
These hoods permit a stable air balance between the ventilation supply and exhaust by incorporating a bypass feature. A restricted bypass is recommended to reduce the opportunity for hood leakage through the bypass caused by convection currents established when a heat source is used in a hood.
Variable Air Volume (VAV) fume hoods
These hoods maintain constant face velocities by varying exhaust volumes in response to changes in sash position. Because only the amount of air needed to maintain the specified face velocity is pulled from the room, energy savings are possible when the sash is closed.
Supply or auxiliary air hoods
These hoods are not permitted for new construction.
It is very difficult to keep the air supply and exhaust of supply hoods properly balanced. In addition, the supply air is intemperate, causing discomfort for those working in the hot or cold air stream. As a result, the supply vent is often either shut or blocked off, which eliminates any potential benefit of this type of hood. Finally, the presence and movement of the user’s body in the stream of supply air creates turbulence that degrades the performance of the hood.
Ductless Fume Hoods
Portable, non-ducted fume hoods are generally not permitted; however, a portable hood may be used for limited applications (e.g., used inside of an existing hood for a special application, such as odor control or to enclose a microbalance). Such applications must be reviewed and approved by EHS on a case-by-case basis.
Perchloric Acid Hoods
Heated perchloric acid shall only be used in a laboratory hood specifically designed for its use and identified as “For Perchloric Acid Operations.” (Exception: Hoods not specifically designed for use with perchloric acid shall be permitted to be used where the vapors are trapped and scrubbed before they are released into the hood.)
Perchloric acid hoods and exhaust duct work shall be constructed of materials that are acid resistant, non-reactive, and impervious to perchloric acid.
The exhaust fan should be acid resistant and spark-resistant. The exhaust fan motor should not be located within the duct work. Drive belts should not be located within the duct work.
Ductwork for perchloric acid hoods and exhaust systems shall take the shortest and straightest path to the outside of the building and shall not be manifold with other exhaust systems. Horizontal runs shall be as short as possible, with no sharp turns or bends. The ductwork shall provide a positive drainage slope back into the hood. Duct shall consist of sealed sections. Flexible connectors shall not be used.
Sealants, gaskets, and lubricants used with perchloric acid hoods, duct work, and exhaust systems shall be acid resistant and non-reactive with perchloric acid.
A water spray system shall be provided for washing down the hood interior behind the baffle and the entire exhaust system. The hood work surface shall be watertight with a minimum depression of 13 mm (½ inch) at the front and sides. An integral trough shall be provided at the rear of the hood to collect wash-down water.
The hood surface should have an all-welded construction and have accessible rounded corners for cleaning ease.
The hood baffle shall be removable for inspection and cleaning.
Each perchloric acid hood must have an individually designated duct and exhaust system.
Radioactive Material Use
- Fume hoods intended for use with radioactive isotopes must be constructed of stainless steel or other materials that will not be corroded by the chemicals used in the hood.
- The interior of all radioisotope hoods must have coved corners to facilitate decontamination.
- The hood exhaust may require filtration by HEPA or Charcoal/HEPA filters. Where such is the likelihood, the hood must have a bag-out plenum for mounting such filters and fan capacity for proper operation of the hood with the filter installed. The most appropriate location for the plenum is near the exhaust port of the fume hood (i.e., proximal to the hood).
- The cabinet on which the hood is installed shall be adequate to support shielding for the radioactive materials to be used therein.
- In general, glove boxes with HEPA filtered exhausts shall be provided for operations involving unsealed radioactive material that emit alpha particles. Consult with the Radiation Safety Section of EHS for specific requirements.
American with Disabilities Act (ADA) Hoods
Must consult with UNC Chapel Hill’s ADA Compliance Office regarding the number lab hoods to install in facilities, which are accessible to and usable by individuals with disabilities – recommend minimally one ADA hood per laboratory floor. These hoods must provide appropriate work surface heights, knee clearances, reach to controls, etc. to individuals in wheelchairs.
The location of at least one ADA hood per floor will enable disabled individuals to conduct their research without having to transport chemicals, etc. in elevators.
Glove boxes (positive and negative) must meet the type, design and construction of requirements ANSI/AIHA Z9.5
Floor-mounted (walk-in) Fume Hoods
These hoods must meet the type, design and construction requirements of ANSI/AIHA Z9.5
Special Purpose Hoods
These hoods include enclosures for operations for which other types of hoods are not suitable (e.g., enclosures for analytical balances, histology processing machines, special mixing stations, evaporation racks). These hoods must be designed per ANSI Z9.5 and the Industrial Ventilation manual.
Type 316 stainless steel should be used for all parts of the fume hood system ventilation duct as long as compatibility is maintained.
Fume hood interior surfaces shall be constructed of corrosion resistant, non-porous, noncombustible materials such as type 316 stainless steel. These materials shall have a flame spread index of 25 or less when tested in accordance with NFPA method 255, Standard Method of Test of Surface Burning Characteristics of Building Materials. New hoods must not contain asbestos materials. Hoods used for perchloric acid digestion shall have interiors constructed of stainless steel and be equipped with perforated spray pipes behind the top of the baffles for periodic wash downs.
Hood inserts are only permitted for radioactive iodination procedures specifically approved by the UNC Radiation Safety Officer.
Laboratory hoods shall be provided with a means of containing minor spills.
The means of containing minor spills might consist of a 6.4-mm (¼ in.) recess in the work surface, use of pans or trays, or creation of a recess by installing a curb across the front of the hood and sealing the joints between the work surface and the sides, back, and curb of the hood.
There must be a horizontal bottom airfoil inlet at the front of the hood.
Adjustable baffles with horizontal slots must be present in the fume hood interior at the back and top.
Before a new fume hood is put into operation, an adequate supply of makeup air must be provided to the lab.
- The average face velocity of the fume hood is between 100-120 fpm at an 18-in sash height or, for the combination sash, 100-120 fpm with the vertical sash closed and two horizontal sashes open.
- All single-point velocity measurements are 90 fpm or greater at the specified minimum openings.
- Fume hood containment is shown using the ASHRAE 110 smoke test and tracer gas tests in 3 test conditions:
- Two horizontal sashes open (vertical sash lowered)
- Vertical sash at 18 inches
- The sash fully open.
Fume hoods with a vertical sash only must pass the ASHRAE 110 testing for the 18 inch and full open sash positions.
Where the required velocity can be obtained by partly closing the sash, the sash and/or jamb shall be marked to show the maximum opening at which the hood face velocity will meet the face velocity requirements.
An airflow indicator and alarm shall be provided and located so that it is visible from the front of the fume hood. In addition, a magnehelic gauge mounted on the front of the hood and connected to the hood throat shall be installed to monitor hood suction.
Hood alarms will sound locally.
Baffles shall be constructed so that they may not be adjusted to restrict the volume of air exhausted through the laboratory hood. Manual dampers shall be locked in position as soon as the system is balanced.
Fans should run continuously without local control from hood locations and independently of any time clocks unless specifically exempted by the UNC EHS Department.
For new installations or modifications of existing installations, controls for laboratory hood services (e.g., gas, air, and water) should be located external to the hood and within easy reach.
Shutoff valves for services, including gas, air, vacuum, and electricity shall be outside of the hood enclosure in a location where they will be readily accessible in the event of fire in the hood. The location of such a shut-off shall be legibly lettered in a related location on the exterior of the hood.
Each exhaust hood shall be permanently labeled with the unique identification number and the fan ID to which it is attached. Each fan on the roof shall be permanently labeled with its unique ID and a permanent listing of all room numbers, hoods and or general exhausts to which it is attached.
Emergency power circuits should be available for fan service so that fans will automatically restart in proper sequence upon restoration after a power outage.
Fume hood ventilating controls should be arranged so that shutting off the ventilation of one fume hood will not reduce the exhaust capacity or create an imbalance between exhaust and supply for any other hood connected to the same system.
In installations where services and controls are within the hood, additional electrical disconnects shall be located within 15m (50ft) of the hood and shall be accessible and clearly marked. (Exception: If electrical receptacles are located external to the hood, no additional electrical disconnect shall be required).
Hood lighting shall be provided by UL-listed fixtures external to the hood or, if located within the hood interior, the fixtures shall meet the requirements of NFPA 70, (National Electrical Code) and NFPA 45.
The light fixtures must be of the fluorescent type and replaceable from outside the hood. Light fixtures must be displaced or covered by a transparent impact resistant vapor tight shield to prevent vapor contact.
Sash panels (horizontal sliding) must be 12 to 14 inches in width.
Sashes shall be made of safety glass.
Use laminated safety glass when internal temperature is anticipated to be less than 160 °F.
Use tempered safety glass when high internal temperatures are anticipated that will result in sash surface temperatures greater than 160 °F.
- Perchloric acid hoods
- Hoods with wash down equipment
- Hoods that could deposit highly hazardous residues on the ductwork
- Hoods requiring HEPA filtration or other special air cleaning
- Situations where the mixing of exhausted materials may result in a fire, explosion, or chemical reaction hazard in the duct system
Manifold fume hood exhaust ducts shall be joined inside a fire rated shaft or mechanical room, or outside of the building at the roofline.
Horizontal ducts must slope at least 1 inch per 10 feet downward in direction of airflow to a suitable drain or sump.
Ducts exhausting air from fume hoods should be constructed entirely of noncombustible material. Gaskets should be resistant to degradation by the chemicals involved and fire resistant.
Automatic fire dampers shall not be used in laboratory hood exhaust systems. Fire detection and alarm systems shall not be interlocked to automatically shut down laboratory hood exhaust fans.
Duct linings shall have a flame spread index of 25 or less when tested in accordance with NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Materials. Test specimens shall be of the minimum thickness used in the construction of the duct or duct lining.
Duct linings are not recommended. If they are installed then they must meet the above requirement.
Air exhausted from laboratory work areas shall not pass unducted through other areas.
Hood exhaust stacks shall extend at least 10 feet above the roof. Discharge shall be directed vertically upward.
If parapet walls are present, EHS recommends that stacks extend at least 2 feet above the top of a parapet wall or at least 10 feet above the roof, whichever is greater.
Note: The University Architect/Planning Office must be contacted if any building features, such as exhaust stacks, extend above the roofline.
Hood exhausts shall be located on the roof as far away from air intakes as possible to preclude recirculation of laboratory hood emissions within a building. For toxic gas applications, the separation distance shall be at least 75 feet from any intake.
As future gas necessities are difficult to predict, EHS recommends at least 75 feet for all applications.
All building exhaust and air intakes must be modeled to demonstrate that the exhaust air (including generator exhaust) will not be recirculated within the building being constructed nor in nearby buildings. Wind tunnel modeling should be used for complex building and terrain interactions.
Discharge from exhaust stacks must have a velocity of at least 3,000 fpm. Achieving this velocity should not be done by the installation of a cone type reducer. The duct may be reduced, but the duct beyond the reduction should be of sufficient length to allow the air movement to return to a linear pattern.
Rain caps that divert the exhaust toward the roof are prohibited.
Fume hood exhaust is not required to be treated (e.g., filtered or scrubbed) except when one of the following substances is used with content greater than the percent specified by weight or volume:
|Chemical||CAS Reg #||Percent|
|Benzedrine (and its salts)||92875||0.1|
|Methyl chloromethyl ether||107302||0.1|
When used for radioisotope work. In this instance, the fume hood exhaust treatment system must be approved by the UNC Radiation Safety Officer prior to installation and use.
Air exhausted from laboratory hoods and other special local exhaust systems shall not be recirculated.
Exhaust fans shall be located outside the building housing the laboratory or in a separate room that is maintained at negative pressure to the rest of the building and provides direct access to outside for fan discharge ducts.
The minimum penthouse exhaust flow rate is 1 air change per hour.
The preferred method of exhaust noise control is with low static loss air valves and reduced exhaust fan speeds.
Noise attenuators may be used as a last resort if constructed of 304 stainless steel and no packing material is used.