Lessons Learned At DOD Indoor Firing Ranges

1. 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

2. 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 charles.jokel@us.army.mil UNCLASSIFIED

3. 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 charles.jokel@us.army.mil UNCLASSIFIED

4. First Example of Multi-lane Indoor Firing Range Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

5. Second Example of Multi-lane Indoor Firing Range Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

6. Narrower Multi-lane Indoor Firing Range Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

7. 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 charles.jokel@us.army.mil UNCLASSIFIED

8. Special Challenges with Indoor Weapon Noise • Reflections Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

9. The Reflected Ceiling Level is Incorrect Ceiling reflections Primary blast and wall reflection Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

10. Special Challenges with Indoor Weapon Noise • Reflections • Clipping Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

11. Special Challenges; a case in point Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

12. Special Challenges; a case in point Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

13. Special Challenges; a case in point Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

14. 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 charles.jokel@us.army.mil UNCLASSIFIED

15. 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 charles.jokel@us.army.mil UNCLASSIFIED

16. 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 charles.jokel@us.army.mil UNCLASSIFIED

17. Impulse Noise Hazard Depends on: Peak Level and B-duration Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

18. 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 charles.jokel@us.army.mil UNCLASSIFIED

19. Typical Exposure Does, In Fact, Consist of Individually Identifiable Impulses Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

20. Putting it All Together 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 charles.jokel@us.army.mil UNCLASSIFIED

21. Treatment Comparisons • 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 charles.jokel@us.army.mil UNCLASSIFIED

22. Example of a Narrow Multi-lane, Treated Range Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

23. Another Example of Range Surface Treatment Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

24. Treatment Comparison (Effect of Surface Treatment Extends only to Reflected Sounds) Chuck Jokel MCHB-IP-MHC charles.jokel@us.army.mil UNCLASSIFIED

25. Treatment Comparison, Effect on ANOR 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 charles.jokel@us.army.mil UNCLASSIFIED

26. Conclusions • 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 charles.jokel@us.army.mil UNCLASSIFIED

27. Conclusions • 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 charles.jokel@us.army.mil UNCLASSIFIED