The proposed work would identify the exposure conditions that facilitate the potentiation of noise induced hearing loss (NIHL) by the chemical asphyxiants carbon monoxide and cyanide. A strong likelihood exists that these combined exposures produce greater risk of hearing loss than noise alone at permissible exposure levels in humans, based upon positive laboratory animal data, and a preliminary understanding of the mechanisms by which chemical asphyxiants disrupt hearing. Rats will be exposed to various types of noise alone or to noise in combination with carbon monoxide and cyanide to assess both temporary and permanent impairments of auditory function. The principal objective of this investigation is to prevent human hearing loss by determining the exposure conditions that facilitate a synergistic interaction chemical asphyxiants such as cyanide and carbon monoxide and noise. The investigators will determine the relationship between exposure duration, concentration of chemical asphyxiants and noise intensity in promoting a synergistic (greater than additive) interaction as indexed by functional impairment of the cochlea and histopathological investigation. The investigators will also determine the relationship between the noise frequency spectrum and interactions with chemical asphyxiants so that accurate predictions can be applied to work place settings where band limited noise may be present.