Every existing or dust-producing room and every grinding or dust-producing room hereafter constructed shall have mechanical means of collecting and disposing of the lint, dust, shavings or other fine particles of matter produced therein, and the heating of such room shall be by steam or hot water pipes, equipped with guards as provided under Section 15-24-880 for a drying room. Every such means of collecting dust shall be provided with a dust arrester, collector or precipitator, which will prevent the exhausting of particles of matter heavier than air into the atmosphere.
1. General.
(a) Where grinding, polishing, buffing, scratch brushing or abrasive cutting-off wheels, grinding and polishing straps or belts are used in operation producing metallic dust, there shall be provided in the area where dusts vapors, gases or fumes are generated, hoods that are connected to exhaust systems which will remove such dusts, vapors, gases or fumes, and such exhaust systems shall be operated continuously during any such operations on aforesaid equipment and such exhaust systems shall be provided with dust arresters, collectors, separators or precipitators to collect the dust before the air or gases from such exhaust systems are discharged therefrom.
(b) All exhaust systems used to collect metallic dust as aluminum, magnesium or zinc shall be provided with an interlocking electrical control connected to the exhaust fan motor and the electric power source for running polishing, buffing and grinding machines. The interlock shall be so designed that in the event of a power failure in connection with the exhaust fan, it will cut out the power source controlling the polishing, buffing and grinding equipment. In the event a wet-type dust collector is made use of, additional interlocking electrical controls should be provided in connection with the water supply, and should be so designed and installed that in the event of a waterflow failure or inadequate liquid level, there will be an automatic cut-out of the power sources controlling the exhaust fan and the polishing, buffing and grinding equipment.
(c) All exhaust systems intended for the removal of potentially explosive dusts, other than those containing magnesium shall be provided with either a wet-type dust or a dry-type separator.
(d) In instances where the dusts consist principally of magnesium or its alloys, a wet-type collector shall be provided. The exhaust fan shall be on the clean air side of the collector.
(e) All dry-type separators shall be located on the outside of the building. The exhaust duct leading to the separators shall be of the shortest possible length.
(f) The exhaust discharge from all dust arresters, collectors, separators or precipitators shall be direct to out-of-doors and at such a point to preclude the possibility of the reentry of the exhaust air into the building or adjacent buildings.
(g) The dust removed in dry-type separators shall be discharged into enclosures, bins or receptacles, located on the outside of the building. Their construction shall be of noncombustible materials; cleanout doors shall be provided. Explosion relief vents shall be provided having a net open area of not less than one square inch for each 0.7 cubic foot or fraction thereof. Such vent flue shall be located not less than ten feet measured horizontally or vertically from any wall, roof, or opening.
(h) Exhaust carrier duct systems shall be cleaned at least once a week. Dust collector enclosures or bins and wet-type collector sludge tanks shall be cleaned daily. The deposits shall be removed from the premises and disposed of in a safe manner. Under no circumstances shall dry particles and/or sludge be discharged into the sewer. Written records of cleaning operations shall be maintained on the premises and shall be open for examination at all times.
2. Exhaust System Design Requirements.
(a) All branch pipes shall enter the header pipe at an angle of 45 degrees or less. All bends, turns, or elbows used in exhaust pipes shall be made with a throat radius of two pipe diameters except greater or smaller throat radii may be used to clear obstructions.
(b) All branch pipes shall connect with a header pipe. The area of the header pipe at any point shall not be less than the combined areas of the branch pipes joining it between such point and the small end of the header. Such header pipes shall be connected to an exhaust fan to produce a minimum air velocity in the branch pipes of 4,500 feet per minute or such greater air velocity reasonably required to remove dusts, vapors, gases or fumes generated. Where cradles are used for handling the parts to be ground, polished or buffed, or where swing grinders are used, and large partial enclosures to house the complete operation are required, the opening in such enclosures shall have a minimum average air velocity of 200 feet per minute and shall be connected to branch pipes of an exhaust system of such area as to produce a minimum air velocity of 4,500 feet per minute in the branch pipes.
(c) Dust shall be removed by means of suitable mechanically exhausted hoods or enclosures at each operation. Such hoods shall be so designed, located and placed that the dust or dirt particles will fall or be projected or drawn into the hoods in the direction of the air flow. No wheels, discs, straps or belts, shall be operated in such manner and in such direction that will cause the dust and dirt particles to be thrown into the operator's breathing zone.
(d) The exhaust outlet of the hoods and the branch pipes connected thereto, of grinding wheels on floor stands, pedestals, benches, swing framed are special purpose grinding machines and abrasive cutting- off wheels shall have not less than the following minimum inside diameter. (See Table 15-28-1210(d).)
(e) The exhaust outlet in the hood and branch pipes connected thereto of brush wheels over six inches diameter and all buffing and polishing wheels mounted on floor stands, pedestals, benches or special purpose machines shall have not less than the following minimum inside diameter. (See Table 15-28-1210(e).)
Size of Grinding or Abrasive Cutting-off Wheel – Inches | Minimum Inside Diameter of Hood Outlet and Branch Pipe – Inches | Maximum Wheel Surface (Sq. In.) |
Up to 9" dia. incl. not over 1 1/2" thick | 3 | 43 |
Over 9" dia. to 16" dia. incl. not over 2" thick | 4 | 101 |
Over 16" dia. to 19" dia. incl. not over 3" thick | 4-1/2 | 180 |
Over 19" dia. to 24" dia. incl. not over 4" thick | 5 | 302 |
Over 24" dia. to 30" dia. incl. not over 5" thick | 6 | 472 |
Over 30" dia. to 36" dia. incl. not over 6" thick | 7 | 679 |
Size of Buffing, Polishing and Scratch Brush Wheel – Inches | Minimum Inside Diameter of Hood Outlet and Branch Pipe – Inches | Maximum Wheel Surface (Sq. In.) |
Up to 9" dia. incl. not over 2" thick | 3-1/2 | 57 |
Over 9" dia. to 16" dia. incl. not over 3" thick | 4-1/2 | 151 |
Over 16" dia. to 19" dia. incl. not over 4" thick | 5 | 239 |
Over 19" dia. to 24" dia. incl. not over 5" thick | 5-1/2 | 377 |
Over 24" dia. to 30" dia. incl. not over 6" thick | 6-1/2 | 565 |
(f) In case a grinding, polishing, buffing or scratch brushing wheel is thicker than given in the tables set out herein, the diameter of the hood outlet and branch pipe connected thereto shall not be less than called for by its wheel surface.
When the grinding, polishing, buffing or scratch brushing wheel surface exceeds 679 square inches, the inside area of the hood outlet and branch pipe connected thereto shall be increased in size in the ratio of one square inch of opening to 17 square inches of wheel surface.
(g) Grinding wheels or discs for horizontal single- spindle disc grinders shall be hooded to collect the dust or dirt generated by the grinding operation and the hoods shall be connected to branch pipes of the following minimum diameters:
Size of Wheel or Disc – Inches | Minimum Inside Diameter of Hood Outlet and Branch Pipe (Inches) |
Up to 12" diameter | 3 |
Over 12" to 19" dia. incl. | 4 |
Over 19" to 30" dia. incl. | 5 |
Over 30" to 36" dia. incl. | 6 |
(h) Grinding wheels or discs for double-spindle disc grinders shall have a hood enclosing the grinding chamber and such hood shall be connected to one or more branch pipes of the following minimum diameters:
Size of Wheel or Disc – Inches | Minimum Number and Inside Diameter of Hood Outlet and Branch Pipe (Inches) |
Up to 19" dia. incl. | 1 pipe – 5" |
Over 19" dia. to 25" dia. incl. | 1 pipe – 6" |
Over 25" dia. to 30" dia. incl. | 1 pipe – 7" |
Over 30" dia. to 53" dia. incl. | 2 pipes – 6" |
Over 53" dia. to 72" dia. incl. | 4 pipes – 8" |
(i) Grinding wheels or discs for vertical single- spindle disc grinders shall be encircled with a hood to remove the dust generated in the operation and such hoods shall be connected to one or more branch pipes of the following minimum inside diameters:
Size of Disc – Inches | Minimum Number and Inside Diameter of Hood Outlet and Branch Pipe (Inches) |
Up to 20" dia. | 1 pipe – 4 1/2" |
Over 20" dia. to 30" dia. incl. | 2 pipes – 4" |
Over 30" dia. to 53" dia. incl. | 2 pipes – 6" |
Over 53" dia. to 72" dia. incl. | 2 pipes – 8" |
(j) Grinding and polishing straps and belts shall be provided with hoods to remove dust or dirt generated in the operation and such hoods shall be connected to branch pipes of the following minimum inside diameters:
Strap or Belt Size – Inches | Minimum Inside Diameter of Hood Outlet and Branch Pipe (Inches) |
Up to 2" wide | 3" |
Over 3" wide | For each 2" or fraction thereof increase in strap or belt width, add 1/2" or fraction thereof to the hood outlet and branch pipe size. |
In instances where potentially explosive dusts are removed, an additional branch pipe connection shall be provided at each point of rotational direction change.
(k) Cleanout openings shall be provided in all horizontal runs of ducts, at ten-foot intervals, at such other points as will permit proper cleaning, and wherever dust settlement is likely to occur, such as near bends, pipe junctions and vertical duct risers.
Cleanout openings shall be of a size that will permit ready access to the duct interior. Wherever practical, cleanout openings should be located on the underside of the ducts. Removable caps shall be provided at all horizontal duct tail-ends.
(l) 1. Branch pipe junctions to main pipe shall be made at an angle not greater than 45 degrees and should, for least resistance and best practice, be 30 degrees or less, measured on the centerline of the two pipes.
2. Junctions shall be made at the side or top of the larger end of a transformation piece, except that for specific reasons of balancing the flow, junction may be made with the main pipe section of uniform pipe diameter.
3. Transformation Pieces. Transformation pieces shall be tapered at an included angle not greater than 30 degrees. Transformation pieces shall increase in area by an amount necessary to maintain the air velocity required in the system, and shall be constructed of material equal in gauge to the material of the connecting pipe at the large end.
(m) 1. Materials of Construction. All pipes shall be constructed of not less than the following gauges of metal, or other noncombustible and moisture-resisting material of equivalent strength:
Diameter of Pipe – Inches | U.S. Standard Gauge |
Up to 8" inclusive | 20 |
Over 8" to 18" incl. | 18 |
Over 18" to 30" incl. | 16 |
Over 30" | 14 |
2. Elbows and Bends. All elbows and bends shall be made from material at least two gauges heavier than is required for straight piping of the same diameter, except that for No. 14 gauge and heavier, the elbows and straight pipe may be of the same gauge.
3. Material. Exhaust piping shall be of galvanized or painted black sheet iron or other noncombustible materials of required strength, corrosion and abrasion-resisting properties.
4. Compliance with mechanical exhaust test requirements shall be determined in accordance with Title 14M.
5. Precleaning Metallic Surfaces. All metallic parts, prior to being subjected to grinding, polishing or buffing processes, shall be thoroughly cleansed of all adhering oils, greases and corrosion- protective materials. All parts surfaces shall be free of solvents before being subjected to grinding, polishing or buffing operations. Every tank or vat containing a volatile flammable cleaning solvent shall be provided with an automatically closing close-fitting cover.
(Prior code § 92-110; Amend Coun. J. 9-6-17, p. 55278, Art. II, § 61; Amend Coun. J. 10-7-20, p. 21791, Art. VI, § 100)