b。 Use mechanical recovery systems such as rotary screw conveyors for heavy media (steel shot)。

c。 Consider using pneumatic recovery system instead of mechanical recovery system for plastic media。

6-3。8 Ductwork。  See paragraph 2-4。1。  Do not use spiral lock seam duct。 Size the exhaust ductwork to maintain a minimum transport velocity of 17。8 m/s (3,500 fpm)。 Specify flat backed elbows per the ACGIH IV Manual, Chapter 5, Figure 5-25。

6-3。9 Fans。  See paragraph 2-4。2。  Use centrifugal fans with backward curved blades, whenever possible。 Centrifugal fans with radial blades are less efficient, but still acceptable。 Place the exhaust fan and the outlet ductwork outside of the building。

6-3。10 Weather Stack Design and Location。  See paragraph 2-4。3 for design guidance。

6-3。11 Replacement Air Ventilation Systems。  See paragraph 2-4。5。  Design dedicated mechanically supplied replacement air systems to maintain room static pressures (relative to the atmosphere) ranging from -4。98 to -14。9 Pa (-0。02 to -0。06 in wg)。

Blast booths often do not have mechanical replacement air。 In this case, there is no control over the room static pressure for non-mechanical replacement air systems。 The extra negative pressure reduces exhaust fan performance。 If mechanically supplied replacement air is not feasible, ensure that the room static pressure and the resistance through filters and louvers are included when sizing the exhaust fan。

6-3。12 Heating and Air Conditioning。  See paragraph 2-6。2

6-3。13 System Controls。  Design system controls in accordance with paragraph 2-5 and the following。

a。 Install static pressure sensors at locations that represent the average static pressure in each blasting room。 This will enhance monitoring and maintenance of desired blasting room pressures。

b。 Interlock the blasting tool power supply with the ventilation system's on-off switch。 This will prevent the use of blasting tools without ventilation controls。

6-4 SAFETY AND HEALTH CONSIDERATIONS。  See paragraph 2-7, 29

CFR1910。94(a)(5), and ANSI Z9。4, section 7, for general requirements。 Consider the following。

6-4。1 Respiratory Protection。  Follow the guidelines in 29 CFR 1910。94(a)(5) for respiratory protection requirements。 The operator must wear a continuous-flow, air- line respirator that covers the head, neck, and shoulders。 Consider providing each respirator hood with an adjustable, vortex-type climate control system。

6-4。2 Air Supply and Air Compressors。 For large booths, consider providing multiple air hose connection points along the perimeter of the enclosure to accommodate work in various parts of the booth。

6-4。3 Noise。  See paragraph 2-7。2。  Carefully select the blast nozzle。 Nozzle noise generation depends greatly on the discharge velocity。 Consider using sound barriers or dampening materials on enclosure walls。 Protect the dampening material

from abrasive blast as much as possible。 Isolate the air compressor, media recirculation, and air pollution equipment to minimize noise exposure。

6-4。4 Hygiene Facilities。  Provide change rooms and shower following guidelines such as OSHA regulations, DOD, or Branch Service requirements。