OSHA General Industry Standards (29 CFR Part 1910) 1910.94: 1910.94 Ventilation

Sets ventilation and protection duties for three dust and vapor generating operations. (a) Abrasive blasting (any forcible application of an abrasive by pneumatic or hydraulic pressure or centrifugal force; not steam or hydraulic cleaning without abrasives): the employer must consider the composition and toxicity of the dust from abrasives and surface coatings and keep respirable dust or fume in the breathing zone of the operator and other workers below the 1910.1000 limits. Combustible organic abrasives are used only in automatic systems; where explosive dust mixtures may occur, equipment follows ANSI Z33.1-1961 (NFPA 91) and subpart S, nozzles are bonded and grounded, and enclosures, ducts and collectors have explosion venting away from occupied areas. Blast-cleaning enclosures are exhaust ventilated to keep continuous inward airflow at all openings, with baffled inlets, blast shut off and exhaust run before opening, screened safety glass, and slit baffles inspected and replaced. Exhaust systems conform to ANSI Z9.2-1960 and Z33.1-1961; dust leaks are repaired promptly; static pressure drop is checked at completion and periodically; recirculating systems need an abrasive separator; exhaust passes through dust collectors emptied without contaminating other areas. Only NIOSH-approved (42 CFR part 84) respirators are used; abrasive-blasting respirators are worn inside blast rooms, in manual silica sand blasting not separated from the operator, or where toxic dust may exceed 1910.1000 limits; properly fitted dust-filter respirators may be used for short, intermittent or occasional exposures where dust cannot otherwise be controlled, and for outside blasting with nonsilica abrasives on low-toxicity materials, but never for continuous protection with silica sand or toxic materials; a 1910.134 respiratory protection program applies; operators wear gloves and aprons, and safety shoes per 1910.136(b)(1) where heavy pieces are handled, and eye and face protection per 1910.133; respirator air meets 1910.134(i); dust and spilled shot are cleaned up. (b) Grinding, polishing and buffing of metals: where dry operations cause exposure above 1910.1000 or other limits, local exhaust ventilation must be provided and used. Hoods must direct particles into the airflow and meet minimum exhaust volumes in Tables G-4 to G-9 (for example 220 cubic feet per minute for grinding wheels up to 9 inches diameter and 1 1/2 inches wide), with recommended duct velocities of 4,500 feet per minute in branches and 3,500 in mains; cradle and swing-frame enclosures at least 150 feet per minute over the opening; portable grinding in partial enclosures at not less than 200 feet per minute face velocity; bench grinder hood tongues adjusted within one-fourth inch of the wheel; hood strength per 1910.215 Tables O-1 and O-9; systems tested per ANSI Z9.2-1960 and fitted with dust collectors. (c) Spray finishing: all operations enclosed in spray booths or spray rooms built to 1910.107 and NFPA 33-1969 location rules, with noncombustible construction, walkways at least 6 1/2 feet high, exits at least 3 feet wide (2 feet with multiple exits within 25 feet) opening outward, minimum air velocities per Table G-10, total exhaust diluting solvent vapor to at least 25 percent of the lower explosive limit, NIOSH-approved respirators for operators downstream of the object sprayed, filter pressure gauges marked for change-out, make-up air equal to exhaust, heated to not less than 65 F where outdoor temperatures stay below 55 F, and direct gas-fired make-up air limited to 200 ppm carbon monoxide or 2,000 ppm total combustible gases on flame failure. Exteriors of buildings, fixed tanks and small portable sprayers not used repeatedly in one place are excluded.