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Design Criteria for Laboratories

  1. Fume Hoods

    1. Fume Hood Selection

      1. Hood design.

        1. Laboratory hoods are to be considered an integral part of the overall building HVAC system, should provide adequate safety for all users and be included in overall energy efficiency planning.

        2. Designers shall do a pre-project analysis of fume hood safety and energy conservation strategies and present recommendations during the initial project-planning phase. Strategies to be considered should include such things as: modes of hood operation during work activity and after hours; use of heat recovery loops; use of horizontal sliding sashes, etc.

        3. Recirculation of any laboratory fume hood exhaust air is prohibited.

        4. Consideration shall be given to installing combination high efficiency particulate air (HEPA) and/or organic vapor (OV) filters for laboratory fume hoods or individual exhaust duct systems where compliance with the National Emission Standards for Hazardous Air Pollutants (NESHAP) may be an issue.

        5. Designers shall specify fume hood exhaust ductwork based on good safety and engineering principles.

        6. During schematic design, the institution user group(s) shall provide the designer with a complete list of chemicals anticipated for use to assist in the selection of appropriate exhaust duct materials.

        7. The exhaust ductwork materials shall be selected based on code compliance and compatibility with the chemicals and agents planned for use.

        8. Ductless fume hoods are prohibited.

        9. Low airflow safety alarm consoles shall be factory and field-tested and furnished with each fume hood. Airflow measuring devices shall be capable of indicating design flow-rates and +/- 20% of design flow rates.

        10. Locations of plumbing and electrical service connections shall be determined from the supplier’s rough-in drawings.

      2. Fume hood size.

        1. Fume hood sizes shall be selected according to intended use and available space.

        2. Three-foot and four-foot width hoods shall be selected when the intended use is for one person and when large apparatus set-ups are not anticipated.

        3. Five-foot width hoods shall be selected when the intended use is for one or two people and where large apparatus may be set up some of the time. Hoods greater than five-foot width shall not be used for any radiation or perchloric acid activities.

        4. Six-foot width general-purpose hoods shall be selected when the intended use is for two or more people, in teaching labs, or when unusually large apparatus may be set up a majority of the time.

        5. Fume hoods longer than six-feet are not permitted in any laboratory, since the hoods cannot exhaust effectively into a single duct chamber. Variances to this requirement may be considered on a case-by-case basis with proper justification and should be submitted to the Board of Regents Vice Chancellor for Facilities prior to beginning the project.

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    2. Fume Hood Airflow Requirements

      1. Airflow rate.

        Standard bypass, constant volume fume hoods and variable air volume (VAV) hoods shall be designed to maintain a face velocity of 100 feet per minute (fpm), +/- 20%, with the sash open 18 inches. This requirement applies to general purpose, special purpose, radiation, and perchloric acid hoods. In addition, alternative fume hood design strategies which may be capable of maintaining the required level of safety and capture efficiency at lower face velocities may be considered on a project-by-project basis. Documentation verifying safety and capture efficiency performance of the proposed alternative fume hood design strategy shall be provided by the project designer in advance to the engineering and environmental health and safety departments at the institution for use in their decision-making process. If the institution decides to employ such an alternative fume hood design strategy, written justification – including a summary statement of the institutions preference and capability to maintain the system – must be provided as part of the preliminary design documents and must be specifically presented at the preliminary design meeting at the Board of Regents Office of Facilities.

      2. Air passage.

        1. Non-bypass constant volume fume hoods are prohibited.

        2. Variable air volume (VAV) fume hoods may be considered for general or special purpose hood applications only. They must be capable of maintaining the required hood face velocity (100 fpm =/-20%) and have a low airflow alarm installed as noted under parts V-B-1 / V-G-5.

        3. Auxiliary-air hoods are not permitted in new laboratory construction or renovation projects, but may be considered on a case-by case basis for general-purpose and special-use hood activities only if special energy conditions or design circumstances exist. If approved, they must distribute in-flow air uniformly at the air supply opening at 70% or less of total exhaust volume. Down-flow velocity should not exceed 30 feet fpm at the plane of the down-flow air opening.

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    3. Fume Hood Types

      Laboratory fume hoods shall be either standard bypass constant volume or variable air volume (VAV). High performance low volume (HPLV) fume hoods or auxiliary air hoods may be considered for approval on a case by case basis.

      1. Standard bypass hoods.

        Standard by-pass fume hoods provide bypass air when the sash is closed to maintain exhaust air continuously at the same volume and may be selected for desired applications. Note: Non-bypass constant volume fume hoods are prohibited.

      2. Variable air volume (VAV) hoods.

        VAV fume hoods have an air control that varies the exhaust air volume in proportion to the hood face opening by either changing the speed of the exhaust fan or adjusting an exhaust duct damper and may be selected for desired applications.

      3. High performance / low-flow hoods.

        High performance / low-flow hoods are specially designed hoods which are premised on an internal articulating baffle to create greater hood containment efficiency at lower flow rates such as 50-70 lfpm. These hoods may be considered for USG projects on a case-by-case basis as determined via thorough analysis by the project designer, the institution and the Board of Regents Office of Facilities.

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    4. Fume Hood Applications

      1. General-purpose use.

        A bypass type hood with an airfoil and sash is often the hood of choice used to remove vapors, fumes, particulates, or gases generated by chemical reactions in teaching and research laboratories involving acids, organic solvents, and radioactive materials. A stainless steel interior may be specified for radiation work in this type hood. Excluded operations from this type of hood include use of perchloric acid, highly toxic and unstable explosive materials. Note: General-purpose auxiliary-air hoods, designed to furnish up to 70% outside air to be drawn into the hood from a point outside the sash, may be considered on a case-by-case basis for installation on renovation projects only (no new construction).

      2. Radiation use.

        This hood category is used for radioisotope work. Use of perchloric acid, highly toxic, and unstable explosive materials is excluded. Radiation auxiliary-air hoods are prohibited.

      3. Perchloric acid use.

        A bypass hood with a duct and canopy wash-down system is used for laboratory experiments with perchloric acid compounds. These hoods shall not be used for work with sulfuric acid, acetic acid, organic solvents, or any combustible or water-reactive materials. Perchloric acid auxiliary-air hoods are prohibited.

      4. Special-purpose use.

        A uniquely configured hood may be designed and used for a special laboratory purpose, such as enclosing analytical instrumentation or as a canopy device uniquely configured for exhausting nuisance odors, steam, heat or other physical stressors. These type hoods may also be used for hazardous materials (highly toxic, unstable, explosive, corrosive, or reactive), provided they are constructed of materials compatible with the intended use and have appropriate filtration and other control measures in place to effectively capture contaminants.

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    5. Fume Hood Location

      Fume hoods shall be located per the requirements of ANSI/AIHA Z9.5 (most recent version) to minimize excessive airflow cross-drafts in the laboratory, in accordance with sound engineering principals.

      The addition of a new fume hood (or hoods) to an existing laboratory shall require design review and approval by the campus engineering and environmental health and safety departments. This is necessary to determine the adequacy of the existing heating, ventilation and air conditioning system to handle the additional exhaust hood capacity load.

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    6. Submittals

      Shop drawings (required in 1-D-2 above) shall be coordinated with other work involved and submitted for fume hoods showing:

      1. Plans: to include elevation, ends, cross sections, service run spaces, service fixtures (type and location), location and details of anchorages and fitting to floors, walls, and bases.

      2. Layout: units with respect to surrounding walls, windows and doors, lighting fixtures, HVAC registers and other building components, connection to hood exhaust system, location of access doors, cut-off valves and junction boxes, with rough-in drawings provided for mechanical and electrical services.

        Equipment manufacturer’s installation instructions shall be provided, along with their recommended duct connection method(s).

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    7. Fume Hood Components

      1. Approvals.

        Fume hoods shall have UL approval. Approved manufacturers include those who have or may demonstrate through written certification, approved submittals, and performance data (including ASHRAE 110 test) that their fume hoods are capable of maintaining a sustained safe working environment for laboratory personnel.

      2. Base cabinet size.

        The hood base cabinet shall be as wide as the hood superstructure. Base cabinets shall be compatible with and strong enough to support the hood superstructure and countertop.

      3. Supporting countertops.

        Hood working surface countertops shall be as wide as the hood superstructure, strong enough to support it, and be compatible with designated hood service. Countertops shall be provided with a 1/4th to ½-inch raised edge around the interior periphery of the fume hood for spill containment.

      4. Service fixtures

        Service fixtures shall be provided as required in this DC (Section IV-C-1) and specified in the drawings.

        1. All plumbing service fixtures shall be located inside the hood within 12 inches of the hood sash on a common vertical center line and have remote activation handles on the outside of the sash post.

          • Unless otherwise specified, one set of service fixtures, located on one interior side, is sufficient for 3-foot and 4-foot width hoods.

          • 5-foot and 6-foot width hoods shall have two sets of service fixtures inside the hood, one set on each side.

        2. Gas, air, vacuum service fixtures shall be located inside the hood within 12 inches of the hood sash.

          • Unless otherwise specified, one set of each located on one interior side is sufficient for 3-foot and 4-foot width hoods.
          • 5-foot and 6-foot width hoods require two sets of these supply fixtures, one set on each side.

          • Recommended vertical order of installation: gas at lowest position, air at mid-position, vacuum at highest position.

        3. Vertical-discharge water service fixture(s), with vacuum breaker, shall be provided for each cupsink, positioned above to drain directly into it.

        4. Cupsinks shall be provided mounted in the countertop:

          • Unless otherwise specified, 1 cupsink for each water fixture on one interior side of 3-foot and 4-foot width hoods.

          • 5-foot and 6-foot width hoods shall have 2 cupsinks, one for each water fixture, inside the hood on each side.

        5. Electrical service fixtures shall be combination type, mounted at the lowest point on a hood sash post:

          • 2 120-volt A.C., GFCI-protected outlets.

          • 1 or more 240-volt A.C., GFCI-protected outlets.

        6. GFCI circuits provided within the power panel shall be identified as such on the panel facing.

        7. A light switch for interior fixture lamps mounted on an exterior sash post.

        8. Interior lamp fixture having twin fluorescent lamps capable of providing at least 60 foot-candles (f.c.) of illumination as measured across the interior base of the hood.

        9. Perchloric acid and special-purpose hoods provided with an explosion-proof lamp fixture (lamp not to exceed 150-watts unless specified by the manufacturer).

      5. Low airflow alarm console.

        New fume hoods shall be provided with a low airflow alarm console to warn of hood exhaust average airflow velocity falling below 80 fpm or, in the case of approved alternative fume hood designs, more than 20% below the lowest full-open sash face velocity at which the fume hood is approved.

        1. A factory-mounted safety alarm console shall be recess mounted into the hood facing according to alarm console manufacturer’s instructions.

        2. Air velocity sensors, if external, shall be installed and identified per the manufacturer’s instructions, and be easily accessible.

        3. Console shall have plate-mounted or plastic-adhering operating instructions applied on or next to the console. Digital instructions displayed from the console are also acceptable.

        4. Console shall have a digital device calibrated to read average face velocity.

        5. Console shall have an audible alert with sound pressure intensity of at least 65 decibels.

        6. Console shall have an audible and visual indicator to indicate low airflow. The visual indicator shall remain activated if the audible alarm is silenced and until the alarm is reset.

        7. Console shall have a circuit test button to verify operation of the audible and visual alarm components.

        8. A means of disabling the console alerts shall be provided for maintenance, apparatus assembly, etc.

        9. A 6-second delay circuit shall be provided to prevent false alarms when exhaust system is reactivated.

        10. If the hood is connected to an energy management system (EMS), the safety alarm function shall be integrated with and monitored by the EMS system. Also, for hoods having power switches on the hood face, or for hoods having a set-back operating mode, the alarm function shall not activate when power is intentionally turned off or set back.

        11. A contact closure or local area network device capable of indicating a low airflow condition shall be provided as a means to interface with the building airflow control system.

      6. Hood access panels.

        1. Hood interior side wall access panels shall be furnished and properly installed.

        2. No positive pressure ventilation shall be introduced into the hood behind the plane of the sash.

      7. Hood sash.

        1. The front face of the hood shall have a sash frame constructed of the same material as the fume hood with its window made of flame and shatter-resistant (and non-splintering) transparent material.

        2. The sash shall be capable of vertical or horizontal movement to close off the entire front opening.

        3. Vertical sashes shall move throughout their travel by applying no more than 5 lbs. of force. They must remain stationary when force is removed.

        4. Horizontal sashes shall consist of at least two panels, movable throughout their travel by applying no more than 5 lbs. of force. They must remain stationary when force is removed.

        5. Combination sashes (vertical and horizontal) shall meet the requirements for each as noted above.

        6. Factory-installed sash stops shall be provided and installed 18 inches above the working surface, with easy release to open the sash further for set-up work.

      8. Hood airfoil.

        1. Hood airfoil shall be located approximately 1 inch above the hood working surface, securely connected per manufacturer’s instructions.

        2. Airfoil shall provide the bottom stop for the hood sash.

      9. Hood baffle openings.

        1. Interior exhaust openings shall be provided nearly full width across the bottom, center, and top rear of the hood.

        2. Opening size shall range from 1 ½- to 4-inches.

        3. Baffles may be installed over the openings to close them off as desired. If installed, baffles must be mechanically or electrically activated to open or close from the exterior hood face. Interior adjustment knobs or levers are not permitted.

      10. Hood identification nameplates.

        1. Nameplates are required for perchoric acid hoods, reading: “Only reactions with perchloric acid are permitted in this fume hood.”

          Note: Perchloric acid hoods should not be used for non-perchloric acid reactions, because organic material may violently react with perchloric acid if not routinely washed down.

        2. Nameplates are recommended for General Purpose, Radiation, and Special Purpose hoods, reading: “Use no perchloric acid within hood”.

        3. Sign lettering size recommended for hood type is at least 1/2-inch height, with text lettering at least ¼-inch height.

      11. Operating instructions. Manufacturer’s hood operating instructions shall be provided.

      12. Hood filter units.

        1. When hood duct filtration is required for specific contaminants, filtration units shall be located on the building roof or in an otherwise safe and easily accessible area for filter changes.

        2. Inclined manometers, or equivalent devices, shall be provided to indicate filter loading and resulting pressure increases within the duct so filters may be changed as needed.

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    8. Fume Hood Work Surface Materials

      Recommended fume hood interior and work surfaces shall be either:

      General or special-purpose and radiation hoods:

      • Solid-resin (chemical resistant).

      Perchloric acid hoods (and optional for Radiation hoods):

      • Stainless steel.

      Exterior surfaces should be chemical-resistant and color-compatible with lab walls and furnishings.

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    9. Fume Hood Installation

      1. Hood superstructure.

        Fume hoods shall be installed in accordance with requirements in this section, with hood superstructures secured to countertops.

      2. Equipment.

        1. Factory-installed permanent sash stops shall be incorporated into all new laboratory fume hoods, incorporated with a low airflow alarm system as detailed elsewhere in this document.

        2. Lighting fixtures within the hood shall be furnished and installed. General and special purpose and radiation hoods shall have fluorescent lamp fixtures (2 lamps per fixture) rated to provide at least 60 foot-candles lighting intensity measured across the base of the hood. Perchloric acid hoods shall have an explosion-proof rated incandescent lamp fixture provided with a 150-watt bulb (or equivalent lower wattage providing specified illumination).

        3. Static pressure sensors for the low airflow safety alarm console (if used), shall be provided, attached to the alarm console and pre-set into the interface connection.

      3. Fume hood exhaust ducts.

        1. Exhaust duct materials shall be selected and installed based on sound engineering principles. Selected duct materials shall be compatible with the intended uses for the hoods, compliant with existing building/fire code, and appropriately durable.

        2. Roof penetrations for ductwork shall be water-proof and weather-tight.

        3. Exhaust duct seams shall be welded and ground smooth, or otherwise joined using methods and materials providing equivalent leak-proof containment. If duct seams are not to be welded, submittals shall be provided explaining the method and materials to be used.

        4. A minimum of two (2) duct diameters (length) of straight ductwork shall be provided ahead of the exhaust fan inlet to minimize system air turbulence.

        5. Ducting from individual fume hoods shall be installed vertically up with no branch duct tie-ins.

          1. One permitted exception to vertical-up ducting is for duct turns not to exceed 45° from vertical in renovation project installations (not new construction) to avoid building structural members.

          2. Another permitted exception is for horizontal ducting if connected to a manifolded exhaust system.

        6. Duct turns from fume hood to exhaust fan may be smooth radius or gored, limited to 3 turns. Sharp-angle changes of direction are prohibited.

        7. For hoods installed on exterior laboratory walls, offsets are permitted at the smallest angle possible (not to exceed 45°) to connect the duct to the roof fan or manifold system.

        8. Duct damper and valve units shall be located for safe access, in accordance with regulatory standards, for adjustments and maintenance.

        9. The duct interface section furnished as an extension above the hood outlet, shall be made of approved material having smooth connection joints between the hood and exhaust duct. The interface and all flanged gaskets, shall be installed, braced, and properly connected.

        10. Exhaust duct (above interface connection) shall be furnished and properly connected to the exhaust fan.

        11. Perchloric acid hoods shall have a duct and interface wash-down system furnished, installed, labeled, properly connected to drain, and tested to be operational. An isometric drawing showing the piping installation, including stop and drain valves, shall be provided. Proper plumbing connections include connecting the system wash-down lines to the activation handle.

        12. Perchloric acid and special-purpose fume hoods shall be separately exhausted, and not combined with other fume hood exhaust systems.

        13. Hood outlet exhaust flanges shall be of the size needed to provide required airflow through the duct. They shall be pre-drilled for bolting to the ductwork.

        14. Outlet exhaust flanges shall be made of materials deemed appropriate for intended use and installed to minimize turbulence in the outlet or duct.

        15. Ductwork and exhaust stacks shall be sized for acceptable exhaust velocity, measured at the top of the exhaust stack.

        16. Exhaust stacks shall be designed and located in accordance with ANSI / AIHA Z9.5-5.3.5 to prevent re-entrainment of contaminants back into the building.

        17. Exhaust stack height shall be higher than the top of the nearest intake and at least 10 feet above the roof or architectural barrier where located. Aesthetic considerations are not grounds for variances from this requirement. Architectural barriers placed to conceal the stack for aesthetic reasons may be acceptable, provided the exhaust flow is not impeded.

        18. Stacks shall be braced or guy-wired for stability.

        19. Rain caps and other fixtures that may impede exhaust stack airflow are prohibited.

        20. Each duct shall be permanently labeled, where accessible, above the laboratory ceiling, in a penthouse or on the roof, as to the location of the fume hood it serves (listing room number) for maintenance efficiency and to assure the correct hood is selected. Labels must be easily read from the access point.

        21. Exhaust fan units shall be permanently labeled to identify the fume hood they serve.

          1. Exhaust fans and motors for each hood system shall be designed to accommodate at least 10% extra capacity to compensate for normal system loss.

          2. Fan motors shall not operate at design capacity exceeding 90% of motor nameplate horsepower.

      4. Hood exhaust fan system (non-manifold).

        1. Fume hood exhaust fan and motor drive unit shall be located on the building rooftop or in a dedicated mechanical system penthouse, have a weather-protected exterior, and be designed and placed to be readily accessible for visual inspection and maintenance.

        2. All moving parts shall be properly guarded.

      5. Special controls for VAV hoods.

        1. Airflow sensors and pressure independent b (less than 3 seconds) shall be installed in the exhaust duct, desirably at roof level, to maintain face velocity and to prevent backflow or air volume fluctuations.

        2. A closed-loop feedback control shall be provided to directly measure exhaust air volume.

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    10. Fume Hood Performance

      1. Design performance.

        Fume hoods shall be designed to be an integral part of the building HVAC system so that, when connected to an exhaust system, will operate in a safe, efficient manner, within acceptable airflow tolerances as specified in Section V- B-1 (Fume Hood Airflow Requirements).

      2. Hood performance documentation.

        Documentation of hood performance, capture efficiency, and containment effectiveness shall be provided to the institution prior to acceptance of the proposed design strategy. This documentation shall attest that hood performance is adequate for owner’s intended use. The fume hood certifier shall affix a label to face of hood attesting to hood performance.

      3. Hood sound level.

        Hood sound level, when measured at approximately ear level within one foot of the front of the hood, with sash open 18 inches, shall not exceed 63 decibels (dBA). Fan speed shall not exceed 900 rpm, and design-specified noise level for dedicated fan units shall not exceed 60 dBA in the duct at more than 5 feet from the fan inlet.

      4. Low airflow alarm activation.

        Low airflow alarm console shall activate and read out according to the design criteria specified above in this document.

      5. Control valve technology performance documentation.

        VAV hood installations shall have documentation certifying the performance of control valve technology. Note: Plans for use of this technology shall be included as part of the preliminary design documents. This shall be a successful, proven technology with a demonstrated track record of 3 years or more. The performance of these valves shall also be checked after installation to verify performance.

      6. Hood exhaust discharge velocity.

        Hood exhaust for both constant volume and VAV hoods shall meet the discharge velocity requirements of ANSI/AIHA Z9.5 (most current version).

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    11. Laboratory HVAC and Fume Hood System Test & Balance

      1. Installation coordination.

        Designers are responsible to coordinate required installation and testing of air handling equipment and fume hood systems.

      2. Test and balance requirements.

        1. Each hood system shall be carefully checked to assure it was installed in accordance with manufacturer instructions and DC requirements.

        2. While in operation, each hood system shall be tested and balanced to provide specified airflow rates and volumes, with all single air measurements testing to within 20% of the average. Final adjustments needed shall be made before occupancy.

        3. Airflow testing, with fume hood sash set at sash stops (18 inches open), shall be verified as set at 100 feet per minute (fpm). NOTE: Alternative fume hood designs which maintain safety and appropriate capture efficiency at lower face velocities may be considered on a project-by-project basis.

        4. Low airflow alarm console, properly set, shall be verified as activating when airflow drops below 80 fpm or (for alternative fume hood designs) more than 20% below the lowest full-open sash face velocity at which the fume hood is approved.

        5. All control and operating equipment shall be verified as performing within required specifications.

        6. Fume hood operating and maintenance instructions (from the manufacturer) shall be provided and/or affixed to the fume hood.

        7. A copy of the T&B test report shall be furnished as part of final project documentation.

        8. All installation and performance deficiencies shall be addressed and corrected by the contractor before occupancy. Note: Airflow performance shall be verified according to the laboratory HVAC system test and balance report.

      3. Hood certification.

        Upon installation, and before building acceptance, a fume hood certification test, such as the Scientific Equipment & Furniture Association (SEFA) protocol, or equivalent, including face velocity and smoke performance tests, shall verify acceptable hood performance.

        1. Hood exhaust airflow shall be continuous at a rate of 100 fpm when vertical sash is positioned 18 inches open (constant volume and VAV hoods). Single airflow measurements, taken at the plane of the sash, should be within 20% of the average. NOTE: Alternative fume hood designs that maintain safety and appropriate capture efficiency at lower face velocities may also be considered on a project-by-project basis, but in any case shall be within 20% of the established flow rate.

        2. Hoods with horizontal sliding sash shall be tested with sash wide open. Single airflow measurements should be within 20% of the average reading.

        3. Smoke should not escape the hood during the smoke capture test. There should be no dead air pockets or reverse air currents noted within the hood.

        4. Low airflow alarm shall activate when sash stops are over-ridden (sash opened more than 18 inches).

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    12. Exhaust Manifold Systems

      1. Design requirements.

        1. Exhaust manifold systems shall be designed to minimize the number of required fan units needed. Manifold fan systems shall be designed with N+1 redundancy.

        2. Exhaust manifold systems shall be provided with fan systems capable of powering up within 3 seconds and continue exhausting air through the system at the prescribed rate, should one fan motor fail.

        3. All moving parts shall be properly guarded.

        4. Manifold system dampers and control valves shall be accessible for routine maintenance and adjustment.

        5. Individual duct connectors into a manifold plenum shall be permanently labeled as to the fume hood they serve so service and airflow adjustments are made to the right hood.

        6. Ducts exhausting highly hazardous materials shall be appropriately labeled.

        7. Exhaust fans and motors shall be designed to accommodate at least 10% extra capacity to compensate for normal system loss and for possible future expansion. Their maximum design load shall not exceed 90% of motor nameplate horsepower.

      2. Manifold exhaust ducts.

        1. Manifold duct systems must be designed and properly sized to accommodate all duct connections, minimizing internal air turbulence throughout the system.

        2. Branch connections to a manifold duct system shall be limited to 3 turns (smooth radius or gored elbows are acceptable), each not exceeding a 90° angle.

        3. 45° take-off connectors shall connect branch ducts to a manifold to minimize air entry turbulence at the manifold.

        4. Branch connections to a larger size duct shall be offset from one another and appropriately spaced to minimize air turbulence.

        5. Extra manifold connections shall be provided based on anticipated program needs.

        6. Exhaust duct manifolds may be routed horizontally above ceilings to provide appropriate connection points for fume hoods in different locations on the same floor prior to connecting to a vertical duct riser.

          NOTE: Exhaust ducts from other equipment or laboratory apparatus shall only be permitted to connect to the manifold duct if the institution engineering and environmental health and safety departments approve, and if pre-design analysis demonstrates that the system will function properly and safely.

      3. Exhaust manifold system considerations.

        1. Fume hood exhaust manifold systems are approved for use when the design professional deems this as the best method.

        2. Perchloric acid and special-purpose hoods must have their own duct/fan system, or dedicated and labeled manifold system.

        3. Manifold systems shall include sufficient redundancy to maintain continuous negative pressure in lab fume hoods and ducts, as well as provide sufficient exhaust velocity from exhaust ducts. This will include, as a minimum:

          1. A reliable back-up emergency power source linked directly to the manifold exhaust fans.

          2. Airflow sensors and quick-response valves (less than 3 seconds) or through-the-wall airflow/sash position sensitive valves in each hood exhaust duct to prevent back-flow or significant air volume fluctuations.

        4. One or more spare exhaust fan units (N+1) shall be provided, capable of handling continuous required exhaust volume if one fan unit fails or is down for repair.

        5. Manifolded fume hood exhaust ductwork shall be designed to withstand the maximum pressure that can be generated by the fan. Duct reinforcement and construction methods must exceed the fan ’s capability or a negative pressure release device calibrated for the maximum fan pressure shall be provided.

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