25 October 2004
of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle
Sequencing. Figure 3-4 illustrates the required sequence of air cleaning
Figure 3-4. Sequence of air cleaning devices for asbestos delagging.
Industrial Vacuum System. Provide a low volume, high velocity (LVHV)
central vacuum system at delagging shops to exhaust fibers and dust from power tools
(e.g., grinders and saws) when they are used, as specified in 29 CFR 1910.1001.
Design a central vacuum cleaning system, which consists of a motor
driven exhauster interconnected with bag type separators.
Connect the separator to rigid tubing, which extends throughout the plant.
Terminate the rigid tubing with inlet valves at the various workstations. Provide flexible
hose connections to allow workers to do shop cleanup and to decontaminate their
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.
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.
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.