Abrasive blasting

The concentration of respirable dust or fumes in the breathing zone of any worker shall be kept below the levels specihed in Sec. 1910.94 of the OSHA standard. 

Blast cleaning enclosures shall provide a continuous inward flow of air at all openings during the blasting operation. 

Air inlets and openings shall be arranged so as to minimize escape of abrasive and dust particles into the adjacent work areas. 

The rate of exhaust shall be sufficient to provide prompt clearance of dustladen air within the enclosures after cessation of blasting 

The exhaust system shall run a sufficient time after the blast is turned off to remove dusty air from within the enclosure. 

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To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

SSPC-VIS-1-89, Visual Standardfor Abrasive Blast Cleaned Steel, Steel Stmctures Painting Council, Pittsburgh, Pa., 1989. 

API Publ 2027, Ignition Hazards Involved in Abrasive Blasting of Atmospheric Storage Tanks in Hydrocarbon Service, 2nd ed., July 1988. 

Release at high velocity into zone of very rapid air morion Grinding, abrasive blasting, rumbling, hot shakeout 2.5 to 10... 

Released at high initial velocity into /.one of very rapid nnotion Grinding, abrasive blasting, tumbling 2..5-10... 

In order to remove the generated contaminants associated with abrasive blasting and to ensure visibility into the box, a high exhaust airflow rate is necessary. High flow rates may also be necessary to maintain a large pressure difference to prevent leaks of highly toxic and radioactive materials. 

When glove boxes are used for abrasive blasting, their design must take into account that the ejector of the abrasive material is driven by compressed air. This influences the chosen flow rate, which should be large enough to generate an air velocity of at least 3 m s" in the openings. The necessary exhaust airflow rate recommended by INRS is then... 

The ACGIH - recommends 20 air changes per minute for a glove box for abrasive blasting. With a volume of 1 m this is equal to 0.33 s k They also recommend an inward air velocity at all openings of at least 2.5 m s"F... 

There are many different combinations of supply inlets and exhaust enclosures, where the system has been designed as a whole. Two of these enclosures are described in some detail abrasive blasting rooms with a person working inside the enclosure, and hospital isolation rooms. 

It should be noted that the primary purpose of the ventilation systems described for abrasive blasting rooms and hospital isolation rooms is to prevent or minimize exposure to hazardous substances in those persons working outside the blasting or isolation room. The ventilation system may also reduce exposure for workers inside these rooms, but often the reduction is not sufficient to eliminate the need for respiratory protection. 

Abrasive Blasting Rooms with Person Inside... 

The ventilation in an abrasive blasting room has three main tunctions. The first is to transport the generated dust to the exhaust during the work in such a w ay that good visibility is achieved. The second is to eliminate, as fast as possible, the dust in the room after the work has ended. 7 he third is to prevent unrestricted dispersal and backwash on the blast operator and the machinery and to keep the dust inside the room, preventing exposure to personnel working outside the room. 

There are very few design recommendations. 7 he following ones are taken from the literature. The NIOSH reference covers nearly all aspects of how to design an abrasive blasting room. ... 

TABLE 10.13 Recommended Air Changes for Abrasive Blasting Rooms ... 

J. L. Goodier, E. Boudreau, G. Coletta, and R. Lueas. Industrial Health and Safety Criteria for Abrasive Blast Cleaning Operations. HEW Publication no. (NIOSH) 75-122. NIOSH (. krthur D. Little), 1974. 

Abrasive blasting The process of product cleaning by the use of an abrasive material. 

Abrasive dusts Dusts used for abrasive blasting, grinding, polishing, and buffing. 

Abrasive blasting is generally the most suitable and reliable method of obtaining a visually clean surface and a... 

Dry abrasive blast cleaning should be used on new steelwork where the main contaminant is mill scale. For heavily rusted and pitted steelwork, increased durability can be obtained by the use of wet abrasive blasting where this is practicable. The water will be more effective in removing the potentially destructive and corrosive soluble iron-corrosion products that form at the bottom of corrosion pits. 

Very high standards of surface preparation are necessary, e.g. abrasive blast cleaning to Sa2y, BS7079 Part Al, 1989 for steel components... 

After major surface contaminants have been removed, e.g. by wet abrasive blasting of hot-rolled structural steel, application of a thin coat of an etch primer greatly reduces the incidence of underfilm corrosion, presumably by eleminating localised areas of poor adhesion. Phosphate pretreatments followed by effective rinsing have a similar effect over cold reduced sheets. 

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