Edward L. Zechmann

Noise exposure profiles for small-caliber firearms from 1.5 to 6 meters

Small caliber firearms (rifles, pistols and shotguns) are commonly used at outdoor firing ranges for training in shooting skills, job qualification and for recreation. Firearm noise from fifty-four weapons was measured at an outdoor range in the near field (6 meters and closer) of the weapons using a radial array of 18 microphones centered on the shooter’s head. Each weapon was fired five times and the microphone array was sampled at 200 kHz with at least 16-bit resolution. Peak sound pressure levels and damage risk criteria (e.g. MIL-STD 1474D, 8-hour Equivalent A-weighted Level (LAeq8), and Auditory Hazard Assessment Algorithm for Humans (AHAAH)) were computed for each microphone and compared across weapon type, caliber and load. The acoustic propagation from the muzzle to the microphone was modeled using a simple image source over a reflecting plane. The impedance of the ground was estimated from the observed data and was used to compare the measured waveforms with the estimated waveforms. These data w...

Measurements of bone-conducted impulse noise from weapons using a head simulator

High-intensity impulse sounds are generally considered to be more damaging than continuous sounds, so understanding the attenuation performance of hearing protection devices against impulse noise is key to providing adequate protection for exposed persons. The maximum attenuation of hearing protection devices is limited by bone-conducted sound. Weapon fire noise in the form of short duration impulses can reach peak levels of 170 dB SPL at the shooter’s ear, a sound level for which maximum hearing protection is recommended and for which bone-conducted sound will be a significant factor. However, current acoustic test fixtures do not capture the bone-conducted sound paths. In this study, an anatomically correct head simulator built specifically to measure bone-conducted sound was used to evaluate the effects of impulse noise generated by hand guns and rifles at several peak sound pressure levels ranging between 120 dB SPL and 170 dB SPL. Time histories of the acceleration of the temporal bones and the sound...

Noise source identification and control of a contractor grade table saw

Sponsored by the National Institute for Occupational Safety and Health (NIOSH) as part of their initiative to explore noise reduction strategies for construction equipment, a team of engineering students at Iowa State University studied a contractor grade table saw. Based on standards, published work, and preliminary tests, a repeatable noise measurement procedure was developed for the table saw operation. The wood‐feed rate and force were measured. With the saw operating in a standard and consistent manner, noise sources on the saw were identified using sound intensity measurement techniques and through the application of noise control strategies to individual sources. At this stage, noise control strategies, such as enclosing the motor, are effective for noise source identification but not practical. The effectiveness of both approaches to identifying the noise sources will be discussed. Based on rank ordering the contribution of each noise source to the overall sound levels, permanent noise control strategies are suggested.

Angle dependent effects for impulse noise reduction for hearing protectors.

The proposed U.S. Environmental Protection Agency regulation for labeling hearing protection devices (HPDs) includes an impulsive noise reduction rating. In 2009, the American National Standards Institute Subcommittee for noise approved a revised standard for measuring the impulsive insertion loss of HPDs, ANSI/ASA S12.42‐2009. The exposure at the ear in response to a forward‐propagating wave depends strongly on the orientation of the head with respect to the direction of propagation. Furthermore, the insertion loss varies with the peak sound pressure level. This paper reports the results of tests performed using an acoustic shock tube to produce peak impulses of approximately 160‐dB peak sound pressure level. Two manikins were evaluated: the GRAS KEMAR manikin equipped with 1/2‐ and 1/4‐in. microphone in a GRAS 711 IEC coupler and the Institute de Saint Louis manikin equipped with a Bruel & Kjaer IEC 711 coupler equipped with a 1/4 in. microphone. The manikin heads were rotated through ±90 deg relative t...

Development of an Experimental Method to Estimate the Operating Force of a Hand-Held Power Tool Utilizing Measured Transfer Functions

Hand-arm vibration syndrome (HAVS) collectively refers to diseases caused by prolonged exposure to intensive hand-transmitted vibration, which has been affecting millions of workers who use hand-held power tools. The force interacting between a hand-held power tool and the work-piece is valuable basic information in studying hand-arm vibration problems, however cannot be measured directly. An experimental method is developed to estimate this tool force by utilizing the input point impedance of the hand and measured transfer functions of the tool. The developed method is applied to calculate the tool force of a hand-held grinder and a circular saw to demonstrate and validate the method. Possible applications of the method to study hand-arm vibration or tool design are explained.Copyright

Noise mitigation at the Combat Arms Training Facility, Wright Patterson Air Force Base, Dayton, OH

The Combat Arms Training Facility (CATF) at Wright Patterson Air Force Base in Dayton Ohio was evaluated for the effect of noise treatment to the interior of the firing range. Measurements were conducted in 2009 and 2010 before and after noise treatment. Reverberant energy in the range was reduced through the installation of cementatious shredded fiber board and basalt rock wool to the walls and ceiling of the range. No modifications were made to the windows and doors connecting the range interior to adjacent rooms. Prior to the application of noise treatment, the reverberation times (RT60) ranged from about 3.5 seconds at 100 Hz to about 1.3 seconds at 10 kHz. Following application of the noise treatments, the RT60 was reduced to about 1.6 seconds at 100 Hz to 0.5 seconds at 10 kHz. The critical distance for speech intelligibility increased from about 12 feet to about 22 feet in the speech frequencies 800 to 4000 Hz. The Articulation loss of consonants was improved from 22.5 for the untreated range to 7.2 for the treated range. The noise treatments reduced the reverberation time, increased the critical distance and improved speech intelligibility in the CATF firing range.

Developing a method to assess noise reduction of firearm suppressors for small-caliber weapons

Firearm suppressors have the potential to reduce the muzzle blast by diffusing the initial shock wave of a gunshot. Currently, the American National Standards Institute does not have any standards that specifically address suppressor measurements. A recent NATO standard, AEP 4875 has been proposed to characterize suppressor performance, but the scope of this standard does not include suppressor effects at the shooter’s ear. Additionally, the standard requires firing the weapon from an elevated platform 4 meters above the ground with microphones positioned with regular spacing of about 18 degrees at 5 meters from the muzzle. This study evaluated fourteen different firearms with and without a suppressor. Different loads of ammunition were used to vary the speed of the projectile. For ten of the guns, both supersonic and subsonic conditions were measured. Twelve microphones were positioned at 30-degree spacing in 3-meter ring at 1.5 meters above the ground. One microphone was positioned at 1 meter to the left of the muzzle and two microphones were positioned at 15 centimeters from the right and left ears. The suppressors were effective in reducing the peak sound pressure levels between 3 and 28 dB and 8-hour equivalent energy (LAeq8) between 2 and 24 dB.Firearm suppressors have the potential to reduce the muzzle blast by diffusing the initial shock wave of a gunshot. Currently, the American National Standards Institute does not have any standards that specifically address suppressor measurements. A recent NATO standard, AEP 4875 has been proposed to characterize suppressor performance, but the scope of this standard does not include suppressor effects at the shooter’s ear. Additionally, the standard requires firing the weapon from an elevated platform 4 meters above the ground with microphones positioned with regular spacing of about 18 degrees at 5 meters from the muzzle. This study evaluated fourteen different firearms with and without a suppressor. Different loads of ammunition were used to vary the speed of the projectile. For ten of the guns, both supersonic and subsonic conditions were measured. Twelve microphones were positioned at 30-degree spacing in 3-meter ring at 1.5 meters above the ground. One microphone was positioned at 1 meter to the lef...

The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

Abstract Objective: This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. Design: The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. Results: The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB LAeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. Conclusions: Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.

Evaluation of noise exposures and hearing loss at a hammer forge company

The NIOSH health hazard evaluation program evaluated employees’ exposures to high level continuous and impact noise at a hammer forge company. Personal dosimetry data were collected from 38 employees and noise exposure recordings were collected during two visits to the facility. Extensive audiometric records were reviewed and trends for hearing loss, threshold shifts and risk of hearing loss were assessed. The effectiveness of hearing protection devices for hammer forging was evaluated with an acoustic test fixture. A longitudinal analysis was conducted on the audiometric data set that included 4750 audiograms for 483 employees for the years 1981 to 2006. The analysis of the audiometric history for the employees showed that 82% had experienced a NIOSH-defined hearing threshold shift and 63% had experienced an OSHA-defined standard threshold shift. The mean number of years from a normal baseline audiogram to a threshold shift was about 5 years for a NIOSH threshold shift and was about 9 years for an OSHA t...

Evaluation of high-level noise exposures for non-military personnel

Noise-induced hearing loss is often attributed to exposure to high-level impulsive noise exposures from weapons. However, many workers in industries such as mining, construction, manufacturing, and services are exposed to high-level impulsive noise. For instance, construction workers use pneumatic tools such as framing nailers that can produce impulses at levels of 130 dB peak sound pressure level or greater. Miners have exposures to roof bolters and jack-leg drills that produce more of a continuous, but highly impulsive noise. In some areas of manufacturing the exposures include drop forge processes which can create impacts of more than 140 dB. Finally, in the services sector, law enforcement personnel who maintain proficiency with firearms experience the full gamut of small-caliber firearms during training. This paper will examine the noise exposures from recordings that the NIOSH Hearing Loss Prevention Team have collected. The noises will be evaluated with different damage risk criteria for continuous...