Document qdKbZRBdjpwELjddN9Y69g6J5

1010 CHAPTER 46 if: 1954 Guide M{TO . 2. Induced air flow caused by the thermal or stack effect'from sources of ex- treme heat. -_ . / 3. Exhaust volumes insufficient to dilute mixtures of combustible vapor and ~f~ air to less than 20 percent of the lower explosive limit of the combustible. 4. Room air currents caused by cross drafts, spot cooling, motion of machinery , or operators. 5. Local or State regulations may specify larger exhaust volumes for specific opera- , tions. Exhaust volume requirements for many specific operations have been listed in Tables 2, 3, 4, and 5. Table 3.. Exhaust Requirements*7 fob Grinding, Polishing, Buffing, Scratch Brushing Abrasive Cut-Off Wheels, Grinding and Polishing Belts (Air Volume: 4500 fpm in all branches.) (S in. water suction at average hood) Grinding or Cut-Off Wheels Buffing, Polishing, and Scratch Brushing In. -g 10-16 17-19 20-24 25-30 31-36 Branch Width*, In. Diam, In. li 2 3 4 5 .6 3 4 41 5 6 7 .225 390 500 610 .880 1200 Wheel Diam, Max. Branch In. Width*, In. Diam, In. -9 10-16 17-19 20-24 25-30 2 3) 3 41 45 5 5* 6 61 300 " 500 -- 610 . 740 1040 - Horizontal Single Spindle Disc Grinders Horizontal .Double. Spindle Disc Grinders Vertical Single Spindle Dih Grinders . Wheel Branch Diam, In. Diam, In. -12 13-19 31-36 3 4 5 6 CFM 225 390 610 880 Wheel Branch Diam, In. Diam, In. -19 20-25 26-30 31-53 54-72 1-5 1-6 1-7 2-6 4-8. CFM 610 880 1200 1760 6240 Wheel Branch , Diam, In., Diam, In. CFM-i, -20 21-30 31-53 54-72 v l-4i 2-4 2-6 2-8 500 ~ 1760 ^ Grinding or Polishing Beltb: `. To 3 in. wide--3 in. branch, add 1 in. to branch diameter for each 2 in. or fraction increase in belt width over 3 in. . 'j * Increase branch diameter 0.3 in., but not less than i in., for each 1 in. increase in width over dimehsioj noted. ' y- Duct System Design (f The duct system will consist of branch ducts connected to a main du^, which will convey the air from the hoods to the exhaust fan and the;airiu cleaning equipment, if used. Round ducts should be used wherever pos sible. Their gage size and construction differ from air supply practice due to the rougher usage encountered, and in the case of. dusts, to the abrasive effect. . (See later section on Exhaust System Design and Construction Fea tures.) Usual conveying velocities are shown in Table 6. Where solid con taminants are handled, recommended velocities must be maintained through'-^ out the system to prevent material from settling in the ducts and obstructing . the air flow. For conveying of solid, particles, velocities shown in Table n_ Industrial Exhaust Systems 1011 include a reasonable factor of safety, and design velocities may therefore be adjusted to use commercial pipe sizes which are available generally in i-in. diameter steps through 6-in. diameter and 1-in. steps through 16-ini diameter or larger with 2-in. diameter steps for large diameters. For con taminants that are not solids, conveying velocities are based on a balance between the higher resistance and lower first cost of smaller diameter ducts against higher first cost and lower resistance of larger diameter ducts. Table 4. Ventilation Rates for Open Surface Tanks Process Minimum Ventilation Rate Minimum Ventilation Rate CFM CFM Per Sq Ft Hood Opening Per Sq Ft Tank Area Lateral Exhaust (Note 1) Enclosing Hood Canopy Hood' W/L = ratio Tank Length One Open Side Two Three Open Open Open Sides Sides Sides W/L 0-0.24 AB W/L 0.25-0.49 AB W/L 0.50-1.0 AB Plating Chromium (Chromic 'Acid1 - Mist)..:.'. __ .......................... Arsenio (Arsine) ... ................ Hydrogen Cyanide.................. Cadmium.................................. aodising....... ................ .......... Metal Cleaning (Pickling) 75 65 75 75 75 Cold Acid......................... ........ Hot Acid........................... Nitric and Sulphuric Acid... 65 75 75 Nitric and Hydrofluoric Acid. . Metal Cleaning (Degreasing) 75 Trichloroethylene...... 75 Ethyleue_ Dichloride.. Carbon Tetrachloride.. 75 75 trolytic) Not Boiling........................ Boiling................................ Bright Dip (Nitric Acid)... Stripping Concentrated Nitric Acid........ Cone.. Nitric and Sulphuric Acid....................................... Salt Baths (Molten Salt).......... Salt .Solution (Parkeme, Bonderize, etc.) Not Boiling................................. Boiling.......................... .............. Hot Water (if vent, desired) Not Boiling............... ................. Boiling......................................... 65 75 75 75 75 50 90 75 50 75 100 90 100 125 100 125 175 125 175 150 200 175 225 150 90 130 HO 150 130 170 175 125 175 150 200 175 225 100 125 175 125 175 150 200 .175 225 100 125 175 125 175 150 200 175 225 90: 100 150 90 130 110 150 130 170 100 125 175 125 176 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 90 100 150 90 130 110 150 130 170 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 100 125 175 125 175 150 200 175 225 75 75 125 60 90 75 100 90 110 90 100 150 90 130 110 150 130 170 100 125 175 125 175 150 200 175 225 75 75 125 60 90 75 100 90 110 100 125 175 125 175 150 200 175 225 Note 1--Column A refers to tank with, hood along one aide or two parallel sides when one hood is against a . '*all or a baffle running length of tank and as high as tank is wide; also to tanks with exhaust manifold along center line with ^ becoming tank width in W/L Ratio. Column B refers to free standing tank with hood along one side or two parallel sides. Main ducts connecting two or more branches are sized by the same pro cedure. The main should be designed for the total exhaust volume to be handled through all branch ducts. Where exhaust systems handling solids are to provide for a substantial iknvcr.ease of future capacity, required conveying velocities can be maintained jn*!,' Priding open end stub branches in main through which air will be admitted u system until future connection is made. The volume admitted into the main