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Lessons Learned At DOD Indoor Firing Ranges. Chuck Jokel Noise Control Engineer, Army Hearing Program Office. National Hearing Conservation Association Annual Conference 25 February 2011. UNCLASSIFED.

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Lessons learned at dod indoor firing ranges

Lessons Learned At DOD Indoor Firing Ranges

Chuck Jokel

Noise Control Engineer, Army Hearing Program Office

National Hearing Conservation Association Annual Conference

25 February 2011

UNCLASSIFED


PURPOSE: To share information about the challenges of assessing the noise hazard of indoor firing ranges and optimizing solutions for noise control.

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Items covered
Items Covered

  • Indoor ranges and their noise hazard in general

  • Special Operations Command (SOCOM) ranges in particular

  • Special challenges dealing with impulsive noise and complex noise exposures

  • Project Approach; comparison and modeling

  • Modeling details

  • Noise criteria

  • Resulting weapon restrictions for untreated spaces

  • Potential benefit of different kinds of treatments

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED




Narrower multi lane indoor firing range
Narrower Multi-lane Indoor Firing Range

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Socom indoor ranges
SOCOM Indoor Ranges

  • Multiple locations are in various stages of construction

  • All exposed surfaces are acoustically “hard;” either steel or concrete (except behind the most distant firing position, where there is acoustical treatment in the ceiling)

  • Are multi-shooter tactical ranges: weapons may be fired from any point up to about 50 m distance across an approximate 30 m width

  • For these ranges, the control room has a view of the range and the bulletproof glass window faces the range

  • Other occupied spaces in the buildings housing the range are physically isolated

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges with indoor weapon noise
Special Challenges with Indoor Weapon Noise

  • Reflections

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


The reflected ceiling level is incorrect
The Reflected Ceiling Level is Incorrect

Ceiling reflections

Primary blast and wall reflection

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges with indoor weapon noise1
Special Challenges with Indoor Weapon Noise

  • Reflections

  • Clipping

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges a case in point
Special Challenges; a case in point

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges a case in point1
Special Challenges; a case in point

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges a case in point2
Special Challenges; a case in point

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Special challenges with indoor weapon noise2
Special Challenges with Indoor Weapon Noise

  • Reflections

  • Clipping

  • Standard design tools used to control continuous noise do not apply to impulsive noise:

    • Cannot predict sound field using standard equations

    • Cannot predict hazard reduction resulting from using different acoustical materials, making it hard to

      • Determine which material is best to use

      • How much material is needed

      • Where the material should be applied

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Indoor ranges and their noise hazard
Indoor Ranges and Their Noise Hazard

  • Historically, noise studies have shown the firing of any small arms weapon indoors (or outdoors) is hazardous

  • These findings have led to generalized recommendations:

    • Wear hearing protection

    • Line wall and ceiling surfaces with acoustically absorbent materials

    • Double-glaze windows for control rooms

    • Watch out for flanking paths that could conduct noise to other noise-sensitive areas

  • No distinction in treatment of tactical range vs fixed point range

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Project approach
Project Approach

  • Measure levels in physically similarly sized ranges, but one treated, one not treated, to gain some data on treatment benefit

  • Model the situation to enable treatment optimization, and verify the model. Base it on the following assumptions:

    • Each impulse contributes a quantifiable “dose” of noise that depends on the assigned hazard

    • Actual exposures consist of individually identifiable impulses

    • Each impulse either comes directly from the expanding pressure wave originating at the muzzle or from a reflection of that wave, both of which can be calculated from a few close-in measurements

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED



Noise dose
Noise “Dose”

  • The dose concept follows from the MIL-STD 1474D method of accounting for what is a just safe noise exposure

  • For pure impulse noise, the “just safe” noise exposure depends on peak level and B-duration

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Typical exposure does in fact consist of individually identifiable impulses
Typical Exposure Does, In Fact, Consist of Individually Identifiable Impulses

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Putting it all together
Putting it All Together Identifiable Impulses

Table 5. Multiple shooter Doses and Daily ANR for the Untreated Range (All Lanes Occupied),

Based on Impulse Noise Criterion (and Worst Case Measured Levels).

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Treatment comparisons
Treatment Comparisons Identifiable Impulses

  • Tables similar to the one shown on the previous slide were developed for:

    • Measured firing under a steel ceiling covered with plywood bullet traps

    • Measured firing under a steel ceiling covered with plywood bullet traps having 1 inch thick acoustical foam as a surface treatment

    • Predicted firing under a steel ceiling covered with an “ideal” acoustical treatment

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Example of a narrow multi lane treated range
Example of a Narrow Multi-lane, Treated Range Identifiable Impulses

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Another example of range surface treatment
Another Example of Range Surface Treatment Identifiable Impulses

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Treatment comparison effect of surface treatment extends only to reflected sounds
Treatment Comparison (Effect of Surface Treatment Extends only to Reflected Sounds)

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Treatment comparison effect on anor
Treatment Comparison, Effect on ANOR only to Reflected Sounds)

Allowed Number of Rounds per Day (or Bursts for Automatic Weapon Fire) when using Double Hearing Protection, for Indoor Ranges with Three Degrees of Acoustic Treatment

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Conclusions
Conclusions only to Reflected Sounds)

  • The acoustic environment of indoor firing ranges can be modeled with basic input about the noise of weapons involved, physical dimensions of the range, and ordinary descriptors about acoustical performance of room treatments (absorption coefficients)

  • Surface treatments can moderate the effects of reflected sound, altering B-durations and overall energy content of received noise, thus modestly increasing ANR. Audible effects are more pronounced.

  • Improvement is limited by exposure to direct sounds

  • Broadband absorption is needed to provide optimum effect of the surface treatments. 2-inch thick material is better than 1-inch thick

  • In a tactical range, it is necessary to treat the entire ceiling surface area. Not so with a fixed position range. Ceiling treatment should be given first priority; side and rear wall surfaces are of lesser importance

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


Conclusions1
Conclusions only to Reflected Sounds)

  • Spread shooters out whenever possible, but avoid shooting from end lanes if possible

  • Unlike SOCOM ranges, other indoor ranges may cause noise issues outside the range proper

Chuck Jokel MCHB-IP-MHC

[email protected]

UNCLASSIFIED


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