Use local exhaust hoods and high velocity exhaust takeoffs for each hand tool。 Table 3-1 and the ACGIH IV Manual provide examples of tools and exhaust system for specific operations。

3-5。7。4 Ensure proper capture velocity is produced at each local exhaust hood。 Design vacuum systems to reach within 12。7 mm (1/2 inch) of the contaminant source。

3-5。7。5 Design the pickup air-stream to have a velocity of two to three times the generation velocity for particle sizes from 20 to 30 micrometers (20 to 30 micron。) Design for an additional velocity of: (1) four to five times the generation velocity to pull the particles up through 300 U。S。 standard mesh, or (2) six to eight times the generation velocity to pull the particles up through a 20 U。S。 standard mesh。

 TABLE 3-1。  Minimum Volumes and Vacuum Hose Size for Asbestos Operations

Hand Tool Flow rate m3/s (cfm) Hose Size mm (in。)

Pneumatic chisel 0。06 (125) 38 (1。5)

Radial wheel grinder 0。07 (150) 38 (1。5)

Cone wheel grinder, 2 inch 0。07 (150) 38 (1。5)

Cup stone grinder, 4 inch 0。09 (200) 51 (2。0)

Cup type brush, 6 inch 0。12 (250) 51 (2。0)

Radial wire brush, 6 inch 0。08 (175) 38 (1。5)

Hand wire brush, 3 x 7 inches 0。06 (125) 38 (1。5)

Rip out knife 0。08 (175) 38 (1。5)

Rip out cast cutter 0。07 (150) 38 (1。5)

Saber saw 0。07 (150) 38 (1。5)

Saw abrasive, 3 inch 0。07 (150) 38 (1。5)

General vacuum 0。09 (200) 51 (2。0)

3-5。7。6 Design the air volume for no less than two parts of air to one part of asbestos to be captured by weight。

3-5。7。7 Design the vacuum hose length less than 7。6 m (25 ft)。  Locate inlet  valves 9 to 10。7 meters (30 to 35 feet) apart when a 7。6-m (25-ft) length of hose is used。 Locate tool vacuum hose connection on the ends of the workbench underneath the stands。 Size the hose based on:  (1) air volume per hose, (2) number of hoses to be used simultaneously, and (3) air velocity required to convey the material to the separators。

3-5。7。8 Use single-ply, lightweight thermoplastic or polyvinyl chloride (PVC) flexible hose, but limit the usage whenever possible。

3-5。7。9 中央空调系统设计英文文献和参考文献(16):http://www.youerw.com/fanyi/lunwen_87300.html