Where construction work creates or involves hazardous dusts, fumes, mists, vapors or gases, concentrations must stay within 1926.55(a), and any ventilation used as an engineering control is installed and run as this section requires. Local exhaust must stop harmful dispersion and must not pull contaminants through employees' work area; fans, ducts, hoods and separators are designed, maintained and operated with enough air volume and velocity to capture contaminants and carry them to safe disposal. The system runs throughout the operations it serves and keeps running afterwards while an employee remains in the contaminated zone. Exhaust air and collected contaminants discharge outdoors; recirculation to the work area is allowed only if it causes no harmful exposure, and collected dust is disposed of without exposing employees. Abrasive blasting (f): dust composition and toxicity must be evaluated, breathing-zone levels kept below 1926.55; combustible organic abrasives used only in automatic systems; explosion-venting and bonding and grounding of the nozzle where explosive dust may be present. Blast enclosures maintain continuous inward airflow with baffled openings, the blast is shut off and exhaust run before opening, baffles are inspected regularly, exhaust systems follow ANSI Z9.2-1960 and Z33.1-1961, dust leaks are repaired as soon as possible and static pressure drop is checked at completion and periodically. Recirculating systems need an abrasive separator and exhaust passes through dust collectors. NIOSH-approved (42 CFR part 84) abrasive-blasting respirators are worn inside blast rooms, with silica sand in manual blasting not separated from the operator, or where toxic dust may exceed 1926.55; particulate respirators are allowed for short or occasional exposures such as cleanup; a 1926.103 program is required; operators get gloves, aprons, safety shoes where heavy work is handled, and eye and face protection per 1926.102. Respirator air meets 1910.134(i). Dust may not accumulate outside enclosures and abrasive is kept off walkways. Grinding, polishing and buffing (g): where dry work exceeds 1926.55 limits, local exhaust is required, with hoods placed so particles enter them and minimum exhaust volumes per Tables D-57.1 to D-57.6 (recommended duct velocity 4,500 fpm branch and 3,500 fpm main), 150 fpm over cradle and swing-frame enclosures, 200 fpm face velocity for portable grinding enclosures, adjustable tongues within 1/4 inch of the wheel, hoods meeting ANSI B7.1-1970 strength, systems tested per Z9.2-1960, and dust collectors. Spray finishing (h): operations are confined to booths or rooms built of noncombustible material per 1926.66; walkways at least 6 1/2 feet high, exits at least 3 feet wide (or 2 feet with multiple exits and 25 feet or less travel), doors opening outward; airflow per Table D-57.7 and total exhaust diluting solvent vapor to no more than 25% of the lower explosive limit; make-up air equal to exhaust, not above 200 fpm through self-closing openings unless fan capacity still delivers the required booth airflow, heated so replacement air enters at no less than 65 F where outdoor temperatures may stay below 55 F for appreciable periods (unless radiant heating of the operators or general building heating to 65 F is used instead), with no heater inside the booth; filter pressure gauges; where gas-fired make-up heating mixes combustion products into the supply air of a manual booth, an odorized gas, a burner rate that could not yield over 200 ppm CO or 2,000 ppm combustible gas on flame failure, and a delivery fan. Exterior building spraying and small portable sprayers are outside scope. Open-surface tanks (i): tanks are classed A-1 to D-4 by hazard potential and evolution rate; control velocities follow Tables D-57.11 and D-57.12; airflow is measured at installation, hoods and ducts inspected for corrosion or damage at least every 3 months of operation, make-up air is 90 to 110% of exhaust; employees are instructed on hazards, protective equipment and first aid, given impervious boots, gloves and aprons and goggles or face shields; clean water or deluge showers and eye flushes are provided near harmful liquids, one hot-water basin per 10 employees, chromic acid workers get periodic nostril examinations; tank entry requires atmosphere tests (oxygen below 19.5% is unsafe), ventilation, and in emergencies respirators with a trained standby employee; vapor levels in degreasers stay at least half the tank width or 36 inches below the top, whichever is shorter.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.