RT&L FOCUS AREA(S): General Warfighting Requirements (GWR)
TECHNOLOGY AREA(S): Bio Medical
OBJECTIVE: To develop a personal sampling device that allows novice users to accurately measure and document intermediate-level impulse noise and sub-concussive blast exposures experienced by Service Members in realistic operational environments.
DESCRIPTION: Recently there has been a great deal of concern in the US military about the potential cumulative health effects of repeated exposures to sub-concussive blasts. There is a short-term need to collect information about the frequency and intensity of blast exposures that Service Members are being exposed to when they conduct operational training using high-powered weapon systems and other military equipment. There is also a long-term need to develop enduring monitoring systems that can be used to measure all blast and impulse noise exposures a Service Member experiences over the entirety of his or her military career.
Current impulse-noise measurement systems to measure personal exposures are not well-suited to meet these needs. Typically, impulse noise assessments are conducted on individual weapon systems prior to the fielding of that system. These measurements use laboratory grade equipment that is neither compact enough nor durable enough to be used for exposure measurements during field training events. Additionally, this sort of evaluation may not address real world use scenarios where personnel maneuver around the weapon system during firing according to changes in the tactical environment. Changes in position can significantly change noise exposure. Additionally, evaluations of the individual system rarely, if ever, take into account exposure to multiple noise sources concurrently.
Most current technology for measuring long-term exposures to acoustic noise are focused on continuous noises, like the sounds generated by engines or machinery. This type of noise can be measured with noise dosimeters, which are relatively inexpensive, compact, lightweight, and durable enough to be attached to a Service Member’s uniform and left in place for an entire multiday training exercise.
High-level blast exposures that are potentially concussive (i.e. > 180 dB) are more difficult to measure, but the DoD has made a huge investment in the development of wearable blast gauges that can be attached to the helmet or uniform of a Service Member and maintain a count of the number of exposures that occur over a period lasting multiple weeks or even months.
The current gap in measurement systems is in the intermediate range of impulse noises with peak levels between 140 and 180 dB. These impulses are intense enough to saturate the microphones of conventional noise dosimeters, which are unreliable for measuring peak levels above 140 dB. But those levels are not high enough to trigger most current blast gauges, which cannot register impulse noises below 170 dB. A further complication is that Service Members may potentially be exposed to hundreds or even thousands of mid-level impulse noises in a single training session This means that a mid-level impulse noise monitoring system will require much more sophisticated data handling than a blast gauge that may only need to record the five loudest exposures in a two month period.
At present, mid-level impulse noise exposures can only be recorded with relatively fragile and expensive test measurement equipment that has to be set up and analyzed by expert personnel, who are often researchers rather than occupational hygienists or safety personnel. The immediate need is a test measurement system that is---
a) Portable and rugged enough to be worn on the body by a Service Members in operational training environments;
b) At a minimum, capable of measuring impulses in the range from 140 dB to 174 dB, with a desired dynamic range from 120 dB to 184 dB.
c) Capable of providing an immediate report of the number and intensity of the impulse noise exposures experienced by a Service Member over a single 8-12 hour training exercise;
d) Simple enough to be used by safety personnel who do not have specific expertise in impulse noise exposure.
PHASE I: The contractor will develop and demonstrate a prototype system that is---
a) Rugged and compact enough to be worn on the body during operational training. Mechanical characteristics of acceptable field-tested noise dosimeters are listed below.
1. Dimensions: 5 in. x 2.7 in. x 1.5 in
2. Weight: 14 oz
b) Capable of recording all impulse noise events in the range from 140 dB (minimum-182 dB. Data and settings should be stored in nonvolatile memory.
c) Capable of running continuously for a minimum of an 8 hour period.
d) Capable of downloading data and generating a report to include:
1. The number of impulses
2. The magnitude of each impulse
3. The A and B durations of each impulse
The prototype system should be compared to laboratory grade impulse noise equipment when exposed to controlled impulsive noises from sources such as cold gas shock tubes, arc gap generators, or small arms fired from fixed positions. Ideally, the prototype system should be able to match the gold-standard systems within +/- 2 dB for impulses within the dynamic range of the system.
PHASE II: The contractor will build and deliver 10 prototype systems meeting the Phase I specifications. These prototypes will be evaluated by occupational hygiene professionals to assess their usability and suitability for impulse noise monitoring. Prototypes at this stage should be usable during military training operations by personnel who do not have specific expertise in impulse noise exposure. Criteria evaluated will include size, weight, durability, and user friendliness (both in affixing the system to personnel for monitoring and in downloading/reviewing the resulting exposure data).
In addition to the 10 prototypes, the contractor will provide advanced software which generates a report that includes the following risk analyses, in accordance with requirements laid out in MIL-STD-1474E. The report should include Phase I (d) and,
1. AHAAH unwarned (the warned reflex has been widely repudiated as not reliably protective);
2. LAeq 8 Hr; and,
3. LAeq 100 ms
This software should be evaluated by occupational hygienists and safety personnel without impulse noise measurement experience, and will be judged based on user friendliness in downloading, reviewing, and organizing the resulting data.
PHASE III DUAL USE APPLICATIONS: In Phase III, the contractor will focus on manufacturing, sustaining, and refining the noise dosimeter and software systems. Both the Army and Navy Public Health Centers have requirements to monitor occupational noise exposure and have hearing conservation programs that focus on noise hazard identification, hearing protection, and monitoring audiometry. Thus, these intermediate-level impulse noise dosimeters and its associated software systems would be well suited for Government use. These Public Health Centers, as well as installation safety and occupational hygienists, are examples of potential government customers that are interested in acquiring this type of technology. Additional customers for these products may include police departments to monitor for noise exposure during firearms training, and other occupational hygienists and safety professionals which monitor processes with impact or impulse noise such as mining, hammer forging in manufacturing sector, and jackhammering and pneumatic nail gun use the construction industry as examples.
- Meinke, D., Flamme, G., Murphy, W., Finan, D., Stewart, M., Tasko, S., and Lankford, J. Measuring Gunshots with Commercial Sound Level Meters. 2016. Presented at the National Hearing Conservation Association Conference.
- Smalt, C. Acoustic Measurements for Low Level Blast and Auditory Injury. 2020.
- Department of Defense (US). MIL-STD-1474E—Design criteria standard noise limits. 2015 Apr 15.