In 1958, Dan graduated from the United States Military Academy, West Point, and was commissioned a 2nd Lieutenant in the U.S. Air Force, where he served with distinction for 26 years. It was not until the mid-point of his military career that Dan became involved with hearing conservation. Few people in our field realize that Dan is actually a "rocket scientist", and that credit for launching Dan's acoustics pursuits can be attributed to a parking lot. In 1971, armed with a new Ph.D. in aerospace engineering from the University of Colorado, Major Dan Johnson reported for duty to the Aerospace Medical Research Laboratory at Wright-Patterson AFB, Ohio. The lab Commander invited Dan to look around and see where he felt his abilities could best be put to use. Dan dutifully visited each of the lab's buildings. Using the finely-honed analytical skills he acquired in his engineering program, he astutely concluded that parking was a real problem at the lab - a problem, that is, everywhere except at the Building 441/824 complex of the Biodynamics and Bionics Division. Thus, Dan concluded that this location was where his skills could best be put to use. Fortunately for the field of hearing conservation, this was the home of the lab's Biological Acoustics Branch.
Recognition of Dan's potential was immediate. Dr. Henning von Gierke, Director of the Biodynamics and Bionics Division, and Dr. Charles Nixon, Chief of the Biological Acoustics Branch assigned Dan as the project officer and liaison with the U.S. Environmental Protection Agency, tasked to work with the Office of Noise Abatement and Control to develop recommendations for national guidelines on noise levels and criteria for protecting people from noise-induced hearing loss. Dan immediately immersed himself in a broad array of efforts: he directed studies with the Fels Research Institute to understand the effects of recreational, environmental, and occupational noise on human auditory development; he undertook landmark research on the auditory and physiological effects of infrasound; he worked with the National Institute for Occupational Safety and Health to develop methods for calculating the effectiveness of hearing protectors; he conducted and directed research that defined the effects of long-duration (>24 hours) noise on temporary threshold shift growth and recovery, and he developed mathematical models for predicting permanent threshold shifts due to continuous noise exposure and for calculating corrections to account for the influences of intermittency and impulses in sound exposures. Dan integrated the results of this research to develop numerous hearing conservation documents for the Air Force and the Environmental Protection Agency. Dan's analyses explained cause and effect relationships for noise-induced hearing loss, and have since become the basis for the international and ANSI standards on predicting noise-induced hearing damage. For his efforts, in 1977, Dan received from the Air Force the Harry G. Armstrong Award for Scientific Excellence, which acknowledged him as having made the most significant research contribution among the 300 investigators at the Armstrong Medical Research Laboratory. In 1984, after rising to the rank of colonel, Dan retired from the Air Force. At the time of his retirement, Dan was awarded the Legion of Merit - the second-highest non-combat award given on behalf of the United States Air Force.
Upon entering civilian life, Dan promptly grew a beard (which he has since shaved), and found a parking space at Larson-Davis Laboratories. While at Larson-Davis Labs, Dan served as Chief Scientist, and provided technical oversight for the development of a large variety of acoustic and laboratory instruments. He also continued and expanded his advisory role with numerous scientific and professional organizations. Because of his unbiased insight and scientific acumen, Dan was asked to serve first as an advisor and then as a member on the National Academy of Science/National Research Council Committee on Hearing, Bioacoustics and Biomechanics (CHABA). He was active in CHABA working groups that studied hazardous exposure limits to both intermittent as well as steady-state noise, that evaluated human responses to impulsive noise (especially sonic booms), and that developed guidelines for evaluating the environmental impact of noise.
In 1989, Dan's preeminence in the field of impulsive noise exposures led him to answer a call to become the Director of EG&G's Biophysics Operations at Kirtland Air Force Base, Albuquerque, NM. Working with Dr. Jim Patterson and the U.S. Army Aeromedical Research Laboratory, Dan and his colleagues studied the human auditory effects of exposure to free field blast overpressures. Dan was instrumental in developing a unique facility for producing high level blast overpressures and for designing a research protocol to enable his team to safely study the effects of impulsive sounds on humans. This research documented previously unknown interactions between blast overpressures and hearing protector performance. Utilizing these results, Dan and Jim proposed new criteria for protecting humans from high-level impulse noises.
With the completion of his work at EG&G, in 1998 Dan became president of Interactive Acoustics, Inc., in Provo, UT. He also continues to consult in many professional activities. Having served on the editorial boards of Noise Control Engineering and the Journal of Low Frequency Noise and Vibration, he is currently on the editorial board of the Journal of Occupational Hearing Loss. Dan has served on numerous American National Standards Institute working groups, and has chaired ANSI working groups on impulse noise and hearing conservation criteria. Previously the chair of the Accredited Standards Committees S1, Acoustics and S12, Noise, he currently chairs the Acoustical Society of America Committee on Standards. A Fellow of the Acoustical Society of America, he is a past chair of ASA's Technical Committee on Noise. In addition to his membership in the National Hearing Conservation Association, Dan's other society affiliations include the American Industrial Hygiene Association, and the Institute of Noise Control Engineering. As a member of the American Conference of Governmental Industrial Hygienists, he serves on their Physical Agents Threshold Limit Value Committee, and was a key participant in developing current guidelines recommending a daily 85-dBA TLV using a 3-dB exchange rate.
Dan's theoretical and applied research and his work on acoustic standards and committees have created a remarkable scientific legacy. In reviewing these accomplishments, one is struck by the fact that his investigations involved safe human exposure research to the lowest frequencies, the highest intensities, and the longest durations on record! He has distilled the results of his research into practical advice through over 80 scientific and technical publications that continue to benefit everyone interested in preventing noise-induced hearing loss. It doesn't take a rocket scientist to appreciate Dan's contribution to our field, or to recognize how richly he deserves this tribute. However, to those of us who know him, he will always be, first and foremost, an officer and a gentleman. Dan, we salute you.
Mark Stephenson
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