Noise-induced hearing lossFrom Wikipedia, the free encyclopedia"NIHL" redirects here. For for the National Ice Hockey League, see English National Ice Hockey League.This article's introduction section may not adequately summarize its contents. To comply with Wikipedia's lead section guidelines, please consider modifying the lead toprovide an accessible overview of the article's key points in such a way that it can stand on its own as a concise version of the article. (discuss). (March 2014)Noise-induced hearing loss (NIHL) is hearing decrease caused by loud sound. Evidences of NIHL include a history of exposure to loud sound and a hearing loss in a narrow range of frequencies, such as those from gunfire, power tools, explosions and night club music. The best, first option for protecting hearing is lowering the volume at the source of the sound.[1]Currently, hearing loss in mammals is permanent. While frogs, fish, and birds with hearing loss regain their hearing naturally, mammals lost that ability as much as 300 million years ago, and so far scientists have been unsuccessful in solving that problem.[2]Contents [hide] 1 Mechanism2 Types2.1 Acoustic trauma2.2 Gradually developing NIHL3 Prevention4 In the workplace4.1 Among musicians4.2 Workplace standards5 Mitigation6 See also7 References8 External linksMechanism[edit]NIHL occurs when too much sound intensity is transmitted into and through the auditory system. An acoustic signal from an energy source, such as a radio, enters into the external auditory canal, and is funneled through to the tympanic membrane(eardrum). The tympanic membrane acts as an elastic diaphragm and drives the ossicular chain of the middle ear system into motion. Then the middle ear ossicles transfer mechanical energy to the cochlea by way of the stapes footplate hammering against the oval window of the cochlea. This hammering causes the fluid within the cochlea (perilymph and endolymph) to push against the stereocilia of the hair cells, which then transmit a signal to the central auditory system within the brain. When the ear is exposed to excessive sound levels or loud sounds over time, the overstimulation of the hair cells leads to heavy production of reactive oxygen species, leading to oxidative cell death. In animal experiments, antioxidant vitamins have been found to reduce hearing loss even when administered the day after noise exposure.[3] They were not able to fully prevent it.Damage ranges from exhaustion of the "hair" (hearing) cells in the ear to loss of those cells[4]NIHL is therefore the consequence of overstimulation of the hair cells and supporting structures. Structural damage to hair cells (primarily the outer hair cells) will result in hearing loss that can be characterized by an attenuation and distortion of incoming auditory stimuli.Types[edit]The ear can be exposed to short periods in excess of 120 dB without permanent harm albeit with discomfort and possibly pain; but long term exposure to sound levels over 80 dB can cause permanent hearing loss.[5]There are two basic types of NIHL:NIHL caused by acoustic trauma andgradually developing NIHL.Acoustic trauma[edit]NIHL caused by acoustic trauma refers to permanent cochlear damage from a one-time exposure to excessive sound pressure. This form of NIHL commonly results from exposure to high-intensity sounds such as explosions,