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Air Flow.  Air flow of 75 ft per/min or 1.25 ft/sec (22.86 m/min or
0.38 m/sec) across the firing line is recommended, and a minimum acceptableair
flow is 50 ft/min (15.2 m/min).  At a point approximately halfway between the
firing line and the bullet trap, the air flow should be maintained at 2 to 30
ft/min (6.1 to 9.14 m/min).  The flow should be evenly distribute past the
shooter.  It Is important to have the required velocity without it being
excessive at any shooting position.  The design engineer should avoid
excessive entrance air velocity and keep the sonic exposure from the
ventilation system below 85 dBA.  For initial design, the minimum quantity of
total ventilation for a range shall be the greeter of the cross sectional area
at the firing line times the maximum design velocity, 75 ft/min, or the
average range cross-sectional area (downrange of the firing line) times the
maximum downrange velocity of 30 ft/min.  In calculating the cross sectional
area at the firing line, it should be assumed that shooting booth doors are
open. Air Distribution.  A perforated rear wall will provide uniform air
distribution to ensure diffuse, nonturbulent airflow toward the firing line
and laminar airflow downrange to sweep contaminants away from the firing line.
A minimum distance of 15 ft (4.57 m) from the firing line to the perforated
rear wall should be provided.  Ceiling supply systems are permitted in
existing facilities provided the minimum flow of 50 ft/min (15.2 m/min.) at
the firing line is maintained; however, a beck wall supply is preferred. A
minimum of 20 ft/min (6.1 m/min.) must be maintained downrange for
satisfactory visibility.  To maintain the downrange velocity economically
where construction permits, an 8-ft high (2.44 m) cross section (under any
protective baffles) is recommended.  See Figure 1 for indoor range
ventilation.  If separate supply air and exhaust air fans are used, they shall
be interlocked to prevent independent operation.
Exhaust Openings.  An optional set of exhaust openings may be
located approximately 15 ft (4.57 m) forward of the firing line (not over the
firing line) to exhaust not more than 25 percent of the total airflow. The
remainder of the exhaust openings will generally be located at the apex of the
bullet trap area.  Modification of existing ranges to this design is not
required so long as a flow of 50 ft/min is maintained at the firing line. Cross-Contamination.  The exhaust discharge from the range must be
separated from the supply air intake to prevent cross-contamination of lead
fumes unless the exhaust air is filtered prior to discharge.  If range is a
pert of a larger building, exhaust air discharge will not be located where
cross contamination of general building air can occur.  Intake air should be
located to avoid recirculation of exhaust air.
Ventilation Criteria.  For design of the ventilation system, refer
to DM-3.03 and American Conference of Governmental Industrial Hygienists,
Industrial Ventilation Manual Refer to DM-3.03 for criteria for inside
comfort conditions.

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