5-7 SAFETY AND HEALTH CONSIDERATIONS。 See paragraph 2-7。 Provide combination emergency eyewash and deluge showers in the workspace。 See UFC 3- 420-01 for performance requirements on combination units。

CHAPTER 6 ABRASIVE BLASTING FACILITIES

6-1 FUNCTION。 Workers prepare the surface of aircraft, shipboard, mechanical, utility, and other equipment in abrasive blasting facilities for surface coating, welding, and other operations。 This Chapter does not apply to temporary blasting enclosures。

6-2 OPERATIONAL CONSIDERATIONS。 Silica sand is prohibited from use in fixed location enclosures。 Avoid using agricultural media (e。g。 peach pits, rice hulls, walnut shells)。 They are particularly susceptible to explosions。

6-3 DESIGN CRITERIA。 Apply the general technical requirements of Chapter 2 and the specific requirements of this Chapter to ensure the proper function, operation and maintenance of an abrasive blasting facility。 Use this information when assembling a specification package for an enclosure manufacturer or inspecting an enclosure already in place。

6-3。1 Exhaust Air。  Determine the type of dust hazard and the minimum average air velocity through the blasting enclosure in accordance with 29 CFR 1910。94(a), Abrasive Blasting; ANSI Z9。4, Abrasive Blasting – Ventilation & Safe Practices for Fixed Location Enclosures, sections 4, 5, 6 and A7; NFPA 68, Standard for the Processing and Finishing of Aluminum; NFPA 69, Standard on Explosion Prevention; NFPA  70;  NFPA  91;  and  NFPA  654。   Refer  to  NFPA  65;  NFPA  480,                    Storage, Handling, and Processing of Magnesium; NFPA 481, Storage Handling and Processing of Titanium; NFPA 482, Storage, Handling, and Processing of Zinc; and NFPA 485, Storage, Handling, and Processing of Lithium when blasting on materials containing aluminum, magnesium, titanium, zirconium and lithium, respectively。

6-3。2 Blasting Cabinets。  Install baffles around air inlets to prevent abrasive material from escaping from the cabinet。 Use a minimum inward air velocity of 2。54 m/s (500 fpm) at all operating openings。 Discharge the exhaust air outside the building。

6-3。3 Walk-in Blasting Enclosures。  Design the enclosure so that the air flows from either the ceiling to the floor (downdraft), Figure 6-1, or from one wall to the opposite wall (crossdraft), Figure 6-2, and the following:

a。 Consider the geometry of the room and how work pieces are positioned within the room, and the number of workers and their locations when selecting a downdraft or a crossdraft design。

b。 Minimize the area of a blasting room to reduce the volumetric airflow rate。 Allow at least 1。22 m (4 ft) of clearance between the work piece and the ceiling, walls, and doors of the room。 Add extra clearance to accommodate internal fixtures such as tables and hoists。

c。 Isolate the abrasive blasting rooms from other processes, functions and activities, whenever possible。 Place blasting rooms outside, away from administration and other spaces。 Protect the blasting room and related equipment from rainwater and moisture intrusion。 As a minimum, put a roof or cover over the blasting room。

6-3。3。1 Downdraft。 The downdraft design provides superior visibility。 In  addition, a downdraft design is preferred since contaminated air is usually drawn away from the worker's breathing zone。 When more than one operator works in an enclosure, contaminated air generated from one operation is less likely to migrate into the other operator's breathing zone。 Use a perforated plate with 9。53-mm (3/8-in) diameter holes, as shown in Figure 6-1, to uniformly distribute the airflow over the entire cross-section of the enclosure。 Use a perforated duct inside the plenum to help evenly pressurize the plenum。