11 50 00 EDUCATIONAL AND SCIENTIFIC EQUIPMENT

11 53 13 Laboratory Fume Hoods

.01 General Purpose Constant Volume Fume Hoods

General purpose fume hoods shall have double wall end panels with the front of the panel of the hood opening radiused, providing a streamlined section which will insure a smooth, even flow of air into the hood. The hood interior and panels shall be flush with the entrance shape to prevent eddy currents and backflow of air. The area between the double wall ends shall be closed to house the sash counterbalance weight and such plumbing lines and remote control valves as are required. The overall depth of the hoods shall be approximately 37 inches and the working surface shall be approximately one (1) foot less than the overall width of the hood.
At the bottom of the hood opening shall be installed an air foil which presents a streamlined appearance similar to the sides. This foil shall be mounted with a one inch open space between the foil and the bottom front edge of the hood to prevent any backflow of air at this point. The air foil shall extend back under the sash so that the sash closes on top of the foil.
Hoods shall be equipped with an automatic air bypass at the top of the sash opening. The bypass shall limit the maximum air velocity through the face of the hood and provide a relatively constant volume/velocity of air through the sash opening (regardless of sash position) when hood exhaust fan is in operation. The hood bypass shall not be dependent on mechanical or electrical linkage and shall be completely positive in operation. Arrangement shall be generally as shown schematically on the drawings.
The working surface of the hood shall have a six inch wide raised ledge conforming to the interior liner of the hood to confine spillage away from the face of the hood. Working surface to be 1 1/4" cast epoxy resin.
The hoods shall be equipped with a vertical sliding sash, glazed with 3/16" tempered safety sheet. The glass shall be mounted in a polyvinyl chloride extruded frame to eliminate corrosion potential.
The sash shall be counterbalanced with a single sash weight and sash cable system to prevent any tilting of the sash during operation and shall work smoothly and freely in the sash guides when operated from either end of the sash. The sash cables shall be of stainless steel and shall operate on ball bearing sheaves. Spring type counterbalance will not be acceptable.
Hood services shall consist of a cup sink and plumbing and electrical services as shown on the drawings or other type sink as may be shown on the drawings. Plumbing services are to be composed of remote-controlled valves located within the end panels and controlled by handles projecting through the vertical facia panels of the hood. Valves shall be connected to flanges and hose connectors located on the end panels within the hood. The portions of the fixtures exposed within the hood shall be brass and given a chemical resistant metallic bronze finish, or a highly chemical resistant, inert plastic finish, and the portions of the fixtures exposed on the hood exterior shall be high impact plastic. The valve handles are to be identified with index plates, with the service indicated by symbol and proper color code. The fixture services shall be pre-plumbed to the exterior of the hood for easy access.
A two-tube fluorescent light fixture including cool white lamps of the longest practical length shall be provided at the top of the hoods. The light fixture shall be shielded from the hood interior by a 1/8" polycarbonate safety panel sealed into the hood body with chemical resistant rubber channels.

Hoods shall be prewired to National Electric Code standards for 20 amp services. Duplex receptacles shall be 115 volt, 20 amps on separate circuits. (See Detail 11 xx xx.xx) Details are not yet available in WEB-based manual.

Exterior of the hoods shall be constructed of cold rolled steel and shall have the component parts screwed together to allow the removal of the end panels, front end facia pieces, top facia panel, and air foil strips to allow replacement due to damage or to afford access to the plumbing lines and fixtures. Spacers or reinforcements shall be welded to their main parts. All welding shall be completed and the component parts bonderized and painted on both exterior and interior surfaces prior to assembly on the hood. All parts shall be of heavy gauges and have adequate strength for the extremes of operation to which a fume hood may be subjected and the entire structure shall be rigid and strong. The unit shall have its own frame and the exterior metal parts shall not be hung on the liner.
All surfaces exposed in the interior of the hood shall be fiberglass reinforced polyester, 3/16" to 1/4" thick.
Hoods shall be equipped with a removable baffle at the rear of the hood with non-adjustable openings at top and bottom and open down both sides to allow the flow of air through the hood to compensate for type of gases, apparatus or heat source used in the hoods. The baffle shall be free-floating design and removable to allow for cleaning and decontamination of the area behind the baffle and shall be held in place with stainless steel nuts.
A thermal formed, highly chemical resistant, plastic, belled entry cone with female socket for duct attachment shall be provided at top rear of liner. This device shall contain a condensate collection ring at liner roof level with drain capability.
The hood facia panels and the end of the hoods shall be punched to receive four remote controlled service fixtures at each side of the hood. Holes not used for specified fixtures shall have removal plug buttons which can be removed for later addition to service fixtures.
Head exterior panels shall be no less than 18 gauge steel, except that top front panel shall be 16 gauge, and air foil member 12 gauge.

.02 Auxiliary Air Hoods

Auxiliary air hoods shall be constructed the same as general purpose constant volume hoods. Provisions shall be made for the introduction by a separate blower furnished under the Heating and Ventilating contract. Auxiliary air shall be introduced into a plenum dampered by movement of the sash to accomplish the following results and shall be generally as shown schematically on the drawings. The amount of auxiliary air introduced to the hood shall not exceed 50% of the total required for exhaust.
When the sash is open more than 18 inches, all the auxiliary air shall enter the sash face through horizontal and vertical grill around the exterior face of the door in a peripheral direction and mix with the room air entering the hood at a capture efficiency of no less than 85 percent. When the sash is closed, the auxiliary air shall pass into the hood through a bypass at the upper front interior of the hood but shall be unobstructed by any dampering from leaving the hood plenum through the auxiliary air fan system. When the sash is down, some room air shall enter the hood through the bypass discharge grill and the balance under the one-inch high sash airfoil. Exhaust volume and hood static resistance shall be approximately the same with sash in any position.
The add-air system shall be an integral part of the hood as supplied from the factory and not a separate part added on at the project site.

.03 Isotope Hoods

Professional Note: The construction and performance specification for isotope hoods is the same as for General Purpose Constant Volume Hoods, with the following changes which shall be inserted where applicable, also refer to Paragraph 13B.5:

Surfaces exposed in the interior of the hood shall be type 304 stainless steel. The stainless steel, except the work top, shall be 16 gauge with a #2B finish. The work top shall be 14 gauge stainless with a #4 satin finish and is to be made in the form of a watertight pan, 1/2" deep, with a retaining ledge across the front edge. It shall be reinforced with a 10 gauge steel channel at the front and adequate reinforcement at the enter and rear to support a maximum uniform loading of 200 pounds per square foot. The joints of the liner shall be welded continuously and ground smooth. All corners shall be coved with a smooth radius. Interior shall be crevice free.
The entire stainless steel hood interior shall be reinforced with angles and plug-hats to provide a completely rigid assembly and shall be welded together to form a self-supporting hood assembly.
The collar for the exhaust duct attachment shall be of the same size as the exhaust duct and shall be butt welded to the duct.

.04 Perchloric Acid Hoods

Perchloric fume hoods are to be of the same basic construction and to meet the same test requirements as conventional fume hoods specified by the University with exceptions as hereinafter specified.
The hood interior shall be free of all crevices and corners. Vertical intersecting corners shall form a 1/2 inch radius cove. The lining shall be type 316-L stainless steel of 14 gauge thickness. All seams shall be butt welded, ground smooth and polished to a maximum surface roughness of 20 microinches RMS as measured by a Brush Surface Analyzer or a Profilometer. The lining shall be watertight. The work surface shall be dished 1/2 inch and shall have an integral trough at the rear to collect wash-down water and to serve as a sink.
A full-length perforated spray pipe or a series of nozzles, located behind the top baffle, shall be provided. The spray pipe, fittings, nozzles and supports shall be 316-L stainless steel.
All baffles, supports and components in contact with perchloric acid fumes shall be constructed of 316-L stainless steel.
The collar for the exhaust duct attachment shall be of the same size as the exhaust duct and shall be butt welded to the duct.
Accessories shall include five (5) remove controlled fixtures (two (2) gas, one (1) cold water, one (1) hood wash down water, one (1) duct wash down water), four (4) 120 volt AC and two (2) 208 volt AC electric outlets, blower switch with pilot light (of suitable rating to operate the exhaust fan). A face velocity, air flow monitor audio/visual alarm system shall be provided.
All fan components in contact with the perchloric acid fumes shall be 316 stainless steel or Type I, unplasticized PVC. A stainless steel or PVC nozzle system shall be installed in the exhaust duct to wash down the fan and duct work.

.05 Fume Hood Testing

Fume hoods shall be tested for air flow characteristics at the factory in the presence of designated representatives of the Professional and University. The hoods tested shall be those of each type first assembled, and all hoods shall be modified as may be deemed necessary as a result of the tests. The test room shall provide all equipment and test facilities, including variable calibrated, hood exhaust air, room make-up air, and auxiliary air. Air quantities shall be set to reproduce those shown on the Heating and Ventilating drawings for compliance testing, although demonstration tests at other cfm valves may be called for to observe hood flexibility. General purpose and constant volume fume hoods shall have a minimum face velocity of 100 feet per minute. Perchloric and Isotope fume hoods shall have a minimum face velocity of 125 feet per minute.
Test Procedures

Check construction details, materials, finish, sash operation, etc. Adjust hood exhaust quantity. Adjust room inlet air quantity. Adjust auxiliary inlet air quantity (where applicable)

(NOTE: Hood should exhaust slightly more air than that which is supplied to the room to maintain negative pressure in the room.)
Hood to be operated with sash full open, at 0", and 24" open.

Instrumentation and Apparatus Required for Hood Test:

"Alnor" Thermo-Anemometer with probe, scale graduated to read from 0-350 FPM maximum, or equivalent.

NOTE: Instrument shall have factory tested and recalibrated no longer than six months prior to the date of the test.

One (1) to two (2) gallon pan type container with pan sides not over 4" high.
Four (4) to five (5) pounds of dry ice.
Four (4) ounce bottle of Titanium Tetrachloride.
Ten (10) to twenty (20) cotton-tipped swab sticks.
Roll of masking tape.

Face velocity - Average face velocity equals exhaust cfm divided by sq. ft. sash opening. Face velocities taken at nine (9) points shall not vary by more than plus or minus 10 percent from average velocity.
Procedure:

Make a complete traverse of the hood face with a cotton swab dipped in titanium tetrachloride to demonstrate that a positive flow of air is maintained into the hood over the entire hood face. No reverse air flows or dead air spaces will be permitted.
Paint a strip of titanium tetrachloride along each end and across the working surface of the hood in a line parallel with the hood face and six (6) inches back into the hood to demonstrate that no back flows of air exist at these points. The flow of smoke shall be directly to the rear of the hood without swirling turbulence or reverse flows.
Hold a cotton-tipped stick that has been immersed in titantium tetrachloride at the hood room air inlet and raise the hood sash slowly. Observe that the automatic air bypass is open when sash is in 0" to 6" position and closed when sash is open 8" or more.
A smoke bomb (one minute size) shall be discharged within the hood area to show the exhaust capability of the hood and its design efficiency. No reverse air flows will be permitted. Place lighted bomb in the hood area and move it to various places, checking end panels and working surface to verify that no reverse air flows exist at any point. Lower the sash to closed position to verify that a sufficient air volume is flowing through the hood working area to carry away fumes from a massive fume source. Immediately after the smoke bomb stops discharging smoke, the hood area should be purged of smoke.
Place a pan of dry ice in hot water in the hood and observe flow of the heavy, white vapors generated. The flow of fumes shall be carried away to the back of the hood. No reverse flows of fumes along the work surface toward the front of the hood shall occur.
With the sash open, walk past the hood and observe action of the heavy fumes produced by the dry ice in hot water. Fumes should not gather at front edge of working surface of the hood but should sweep readily toward the rear lower baffle opening.

For Auxiliary Air Hoods, add the following tests:

A smoke bomb (one minute size) shall be discharged into the auxiliary air duct ahead of the blower and the flow of auxiliary air down the front of the hood shall be observed. At least 85 percent of the auxiliary air shall be drawn into the hood along with the room air.
With sash closed, check for room air being drawn into hood through bypass and under sash air foil.
With dry ice in hood, stop exhaust fan with auxiliary air fan operating and with sash closed. Check for any expulsion of fumes into room caused by hood positive pressure. Repeat with sash open.

Evaluation of Hood Tests

The purpose of the foregoing tests is to demonstrate that fumes do not escape from the hood under simulated operating conditions. If any fumes did escape during the test, corrective measures must be taken prior to approval of the hood. After design modifications have been made, the entire test is to be repeated until satisfactory performance is attained.

.06 Hood Adjustment and Balancing

After hoods are fabricated, delivered, and installed in the building and prior to the use of the hoods by operating personnel, it shall be the responsibility of the hood supplier to perform final adjustments on hood adjustable baffles, to measure hood face velocities and make recommendations to the Professional should deficiencies be found in the performance of any hoods manufactured by the supplier.
The expenses incurred by the inspection and adjustments of hood dampers shall be borne by the hood supplier who will promptly execute this work upon request by the Professional and the University.

.07 Hood Maintenance Instructions

Maintenance instructions for the hoods shall be provided by the hood supplier in the form of a printed, permanent metal plate affixed to each hood in an easily-readable position.
The plate shall be approximately 5" x 6" and shall list preventive maintenance procedures, appropriate cleaning materials for exposed metal surfaces, and other recommendations or precautionary measures for proper maintenance of the fume hood structure and parts.

.08 Manufacturer's Recommended Safety Procedures

For the benefit of operating personnel, the hood supplier shall provide a separate, printed, permanent, metal plate, approximately 5" x 6" with cautionary operating suggestions, including at least the following:

Maximum sash opening of 24" for safer working conditions.
Check of hood exhaust for proper functioning before use of the hood.
Avoidance of unnecessary exposure of personnel to fumes inside hood.
Safe limits and confines for placement of work inside hood.
Proper location of hot plates inside hood and compensatory measures to combat excessive heat loads.
Establish maximum heat loads inside hoods for safe operation and maximum temperature operating limit of glass in hood sash.
Most desirable sash location for safest hood operation.
Avoidance of overloading hood with equipment/apparatus and blocking air flow.
Corrective measures after spillage inside hood.
Instructions regarding day-to-day storage of corrosive or volatile materials inside hood.
Avoidance of certain explosive materials for which the hood is not designed.

.09 Differential Pressure Switch

Furnish and install a differential pressure switch to measure the differential pressure across each fume hood exhaust system. Should the system fail to exhaust as measured by the differential pressure switch, when the local switch is indexed to "Operational" or "Emergency," an audible alarm shall be sounded locally along with a red light. Provide a time delay to eliminate nuisance alarms at start-up. The audible alarm shall be provided with concealed volume adjustment. Furnish and install a local "silence" switch for the local alarm. The audible alarm and silence switch shall be mounted on or near the fume hood as indicated on the detail on the drawings.

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