gunfire, a largedrum hit loudly, and firecrackers.Gradually developing NIHL[edit]Gradually developing NIHL refers to permanent cochlear damage from repeated exposure to loud sounds over a period of time. Unlike NIHL from acoustic trauma, this form of NIHL does not occur from a single exposure to a high-intensity sound pressure level. Gradually developing NIHL can be caused by multiple exposures to any source of excessive volume, such as home and vehicle stereos, concerts, nightclubs, excessive noise in the workplace, and personal media players. The U.S. Department of Labor's Occupational Safety and Health Administration (OSHA) states that exposure to 85 dB(A) of noise, known as an exposure action value, for more than eight hours per day can result in permanent hearing loss.[6] Since decibels are based on a logarithmic scale, every increase of 3 decibels SPL results in a doubling of intensity, meaning hearing loss can occur at a faster rate.[7] Therefore, gradually developing NIHL occurs from the combination of sound intensity and duration of exposure.Both NIHL caused by acoustic trauma and gradually developing NIHL can often be characterized by a specific pattern presented in audiological findings. NIHL is generally observed to affect a person's hearing sensitivity in the higher frequencies, especially at 4000 Hz. "Noise-induced impairments are usually associated with a notch-shaped high-frequency sensorineural loss that is worst at 4000 Hz, although the notch often occurs at 3000 or 6000 Hz, as well".[4] Doctoral students at the University of Iowa have termed this notch, specific to a noise-induced etiology, a "muna." The symptoms of NIHL are usually presented equally in both ears.[4]Not all audiological results from patients with NIHL match the above description. Often a decline in hearing sensitivity will occur at frequencies other than at the typical 30006000 Hz range. Variations arise from differences in people's ear canal resonance, the frequency of the harmful acoustic signal, and the length of exposure.[8] As harmful noise exposure continues, the commonly affected frequencies will broaden and worsen in severity.[4] "NIHL usually occurs initially at high frequencies (3, 4, or 6 kHz), and then spreads to the low frequencies (0.5, 1, or 2 kHz)".[9]Prevention[edit]NIHL can easily be prevented through the use of some of the most simple, widely available and economical tools. This includes but is not limited to ear protection (i.e. earplugs and earmuffs), education, and hearing conservation programs. Earplugs and earmuffs can provide the wearer with at least 5 to 10 dB SPL of attenuation.[4] According to a survey by Lass, Woodford, C. Lundeen, D. Lundeen and Everly-Myers, which examined high school student's attitudes and knowledge concerning hearing safety, 66% of the subjects reported a positive response to wearing hearing protection devices if educated about NIHL. Unfortunately, more often than not, individuals will avoid the use of ear protection due to embarrassment, lack of comfort, and reduced sound quality.[10]Hearing protection programs have been hindered by people not wearing the protection for various reasons, including the desire to converse, uncomfortable devices, lack of concern about the need for protection, and social pressure against wearing protection.[11]A systematic review of the effectiveness of interventions to promote the use