★ Auditory Hazard Assessment Algorithm for Humans
The Auditory Hazard Assessment Algorithm for Humans is a mathematical model of the human auditory system that calculates the risk to human hearing caused by exposure to impulse sounds, such as gunfire and airbag deployment. It was developed by the U.S. Army Research Laboratory to assess the effectiveness of hearing protection devices and aid the design of machinery and weapons to make them safer for the user.
In 2015 ahaah I was one of two metrics used by the Department of defense to approve military standard MIL-STD-1474E in to regulate the maximum impact of noise from military systems. It is also used by the society of automotive and aviation engineers for the calculation of hazard from the noise of the air cushion and by the Israeli defense forces, analysis of impulse noise.
1. Overview. (Обзор)
Noise-induced hearing loss Nile usually occurs when the auditory system is an increase in hearing thresholds due to exposure to high noise levels, a phenomenon known as temporary threshold shift TTS, and will not return to normal levels. Damage to the auditory system may vary depending on the type of noise exposure. In contrast to the constant background noise often found in industrial environments, transients, produce and firearms demonstrates a very high level of pressure for a very short period of time, usually about several milliseconds. As a result, near-field peak levels measured objects the barrel of the weapon can range from 150 dB for handheld weapons, and over 180 dB for heavy artillery. For comparison, the noise from industrial installations has been measured below the peak levels of 113 to 120 dB.
In order to protect soldiers from hearing loss, the U.S. army joined the military standard MIL-STD 1474, which defines the maximum noise levels allowed for the production of military systems. However, volunteer studies person demonstrated that the standard used since 1997, Mil-std-1474D, overstated the risks associated with impulse noise exposure. Subsequent Hyper ears, based on imprecise estimates of risk of hearing loss is believed to potentially impede verbal communication between soldiers on the battlefield and reduce situational awareness. At ahaah I was specially developed for more accurate evaluation of the risk to human ear from impulse noise by incorporating the acoustic and physiological characteristics of the ear in its analysis, which were not considered in the previous figures. Ahaah I eventually was used in 2015 to completely revise mil-STD-1474E and the development of a new standard known as Mil-std-1474E.
2. Development. (Развитие)
At ahaah I was first developed in 1987, the us army human engineering laboratory Hel, which later became part of the U.S. army research laboratory ARL to investigate the complex interactions between the external, middle and inner ears, and understand the process for hearing loss at the level of the cochlea. Originally designed to work as an electro-acoustic model of the ear, ahaah I is the product of many noise experiment, which, in turn, guided the direction of future research. The first version ahaah I was modeled after existing, available information about cat ear, since most of the physiological and acoustic characteristics and values for the cat was more famous at that time in comparison with humans and can be studied directly. In addition, the ears of mammals were similar enough that you want to adjust the anatomy of the human ear only minor changes to the model. By 1997 ahaah I was modified in the human model, which takes into account the structure of the human ear. In subsequent years ahaah I passed several inspections, including the study of Albuquerque, who was one of the largest in the beginning of the study pulse of human exposure to noise has led to the establishment of a systematic database that documented the impact of impulse noise on man. The results of these studies showed that the ahaah I was correct on 95% of tests with protective ear and 96 percent for all tests. Unlike Mil-std-1474D is a method of forecasting risk, it was recognized that only required 38% of the time in protected hearing.
3. Operation. (Операция)
At ahaah I calculated the auditory hazard of impulse sounds by simulating their transmission based on how he interacted with the electroacoustic model of the basilar membrane in the cochlea. The analysis of wave motion was based on the Wentzel-Kramers-Brillouin method, the WKB wave dynamics. According to estimates by the computer program of the movement of the stapes footplate and uses the WKB approximation for the evaluation of basilar membrane movements. In ahaah I represented the release in the auditory Arus units of risk that are associated with the damage caused by the displacement of the basilar membrane in the inner ear in 23 different places. According to the model, the recommended limit for daily occupational exposure was 200 Arus, any dose in excess of 500 Arus, according to forecasts, will produce permanent hearing loss.
At ahaah I model consisted of a set of proven algorithms which account for different exposure conditions that influenced the risk of permanent risk threshold, such as noise induced hearing protection devices and reflexive middle ear muscle MEM contractions that occur before the onset of stimulus were obtained, which reduces damage to the hearing in the preparation of sound. Unlike the previous energy model damage ahaah I can also accurately predict the extent of damage by analyzing the pressure-time dependence of the sound wave. Using this method, the model was able to determine why a low level of energy, at the entrance of the ear canal was far more dangerous, the higher the energy level, at the entrance to the ear canal headphones protected. The model found that the former were distinguished by the pressure-time dependence than the last, which was able to more effectively transmit energy via the middle ear.
Depending on the availability of hearing protection on different devices, whether the sound came unexpectedly, and where the sound originated - whether in the eld and in the ear canal entrance, or at the eardrum position - ahaah I the model can predict movements in the inner ear, because it was conformal with the structure of the human ear. For free field, the model assumes that the sound arrives directly to the ear canal and calculated the dynamics of the pressure change at the eardrum, taking in the energy transmitted to the stapes as the entrance to the inner ear. For waves recorded at the entrance of the ear canal or the eardrum, the model considers each source in the schema. The displacement of the basilar membrane is computed from the displacement of the stapes and the unit is determined by measuring the total displacement of the waves in 23 different locations on the organ of Corti in the inner ear. The effect of the pulse sound can be mapped to create a visual representation of the process of damage.
4. The Albuquerque Studies. (Исследования Альбукерке)
Held in 1990 and sponsored by the U.S. army command medical research and material research Albuquerque was a series of volunteer human study that aimed to set new limits on the acceptable level of exposure to impulse noise produced by heavy weapons. Classes were held at an air force base Kirkland in Albuquerque, new Mexico where the participants were presented with four different pressure-time signatures on seven different levels of intensity on different sequences, and sequence. The data obtained in these studies formed a large database used to evaluate the effectiveness ahaah I model. In the experiment, the participants sat at the end of the 3-meter pipe, where at the other end, was blown up by various explosives. Various conditions are taken into account, for example, the distance from the participants ear from the tube, the acoustics of the environment, level of hearing protection and the number of pulses, establishing a matrix of possible risks. The audiogram was used before and after each exposure to measure the threshold and the switching threshold. Pressure-time signatures were measured using the bare sensors for all exposure conditions. According to the data obtained from the Albuquerque research, ahaah I model correctly predicted the acoustic hazards in 95% of cases, while Mil-std-1474D was correct only 38% of cases and the weighted energy method was correct only 25% of the time. For all three approaches, the error mainly derives from the ways to re-predicts the values of danger danger.
5. Controversy. (Споры)
In ahaah I was the subject of controversy in relation to its use as a universal metric for acoustic hazards. In 2003 a study in the framework of NATO on impulse noise found that the ahaah I leads to unsatisfactory results for some conditions of exposure, and the resulting report provides conflicting opinions from several specialists. The review for 2010 by the American Institute aibs biological Sciences also concluded that although ahaah I model is a step in the right direction from the point of view of the consideration to such factors as the average muscle contractions the ear in his analysis, he has not yet been fully developed and approved. At ALIS, there were concerns about ahaah I models, able to simulate the acoustic of the dangers in a complex military environment with constant noise from the various machines and weapons are produced at the same time. In 2012, conducted by the National Institute of occupational safety and health claimed that the fight mAam, what was ahaah I used to justify increasing the recommended maximum noise levels were not present in enough people to be used as forms of analysis. The report also notes that the ahaah I do not adequately consider the consequences of secondary effects such as neighboring shooters and staff for security. As of 2015 model ahaah I was not accepted by the community of NATO.
As niosh and the U.S. army aeromedical research laboratory-funded study of classical conditioning, which was an integral part of the warned ahaah I model. In warn mode, the middle ear muscles is assumed to be already contracted. Mode unwarned middle ear muscles contract after a loud sound exceeds the threshold of about 134 dB SPL peak. Several studies conducted in the period between 2014 and 2020 has studied the prevalence and reliability of MEMC. According to a representative national survey of more than 15.000 people, the Prevalence of the acoustic reflex is measured in persons from 18 to 30 years was less than 90%. Subsequent studies that carefully evaluated 285 people with normal hearing to the conclusion that "acoustic reflexes are not universal and should not be included in the criteria for damage risk and health assessment for impulse noise". Early reduction is an integral part warned the answer is not reliable people with normal hearing.
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