exposed to hazardous noise to help prevent noise-induced hearing loss. hpds reduce (not eliminate) the level of the noise entering the ear. hpds can also protect against other effects of noise exposure such as tinnitus and hyperacusis. proper hygiene and care of hpds may reduce chances of outer ear infections. there are many different types of hpds available for use, including earmuffs, earplugs, electronic hearing protection devices, and semi-insert devices. one can measure the personal attenuation rating through a hearing protection fit-testing system. earmuff style hearing protection devices are designed to fit over the outer ear, or pinna. earmuff hpds typically consist of two ear cups and a head band. earplug style hearing protection devices are designed to fit in the ear canal. earplugs come in a variety of different subtypes. some hpds reduce the sound reaching the eardrum through a combination of electronic and structural components. electronic hpds are available in both earmuff and custom earplug styles. electronic microphones, circuitry, and receivers perform active noise reduction, also known as noise-cancelling, in which a signal that is 180-degrees out-of-phase of the noise is presented, which in theory cancels the noise. canal caps are similar to earplugs in that they consists of soft tip that is inserted into the opening of the ear canal. osha requires the use of hearing protection. but the hpd (without individual selection, training and fit testing) does not significantly reduce the risk of hearing loss. for example, one study covered more than 19 thousand workers, some of whom usually used hearing protective devices, and some did not use them at all. there was no statistically significant difference in the risk of noise-induced hearing loss. regulations environmental noise regulations usually specify a maximum outdoor noise level of 60 to 65 db(a), while occupational safety organizations recommend that the maximum exposure to noise is 40 hours per week at 85 to 90 db(a). for every additional 3 db(a), the maximum exposure time is reduced by a factor 2, e.g. 20 hours per week at 88 db(a). sometimes, a factor of two per additional 5 db(a) is used, however, these occupational regulations are acknowledged by the health literature as inadequate to protect against hearing loss and other health effects. in an effort to prevent noise-induced hearing loss, many programs and initiative have been created, like the buy quiet program, which encourages employers to purchase quieter tools and equipment, and the safe-in-sound award, which recognizes organizations with successful hearing loss prevention strategies. with regard to indoor noise pollution in residences, the u.s. environmental protection agency (epa) has not set any restrictions on limits to the level of noise. rather, it has provided a list of recommended levels in its model community noise control ordinance, which was published in 1975. for instance, the recommended noise level for indoor residences is less than or equal to 45 db. noise pollution control in residences is not funded by the federal government in part because of the disagreements in establishing causal links between sounds and health risks, since the effect of noise is often psychological and also, because it leaves no singular tangible trace of damage on the human body. for instance, hearing loss could be attributed to a variety of factors including age, rather than solely due to excessive exposure to noise. a state or local government is able to regulate indoor residential noise, however, such as when excessive noise from within a home causes disturbances to nearby residences. effects on dogs while people are often educated on the effects of noise exposure in humans, there are also different noise exposure effects in animals as well. an example of this would be in dogs, and the noise exposure levels occurring within kennels. dogs experience this noise exposure whether it be a long stay at an animal shelter, or a weekend stay at a boarding facility. organizations like niosh and osha have different regulations when it comes to the noise exposure levels in industrial workers. currently there are no regulations related to the noise exposure for dogs even with such damaging effects related to their health. health risks dogs are exposed to include ear damage and behavioral changes. the average noise exposure in a kennel is greater than 100 db spl. according to osha these levels would yield in the use of hearing protection for the workers of those kennels due to the risk of noise induced hearing loss. the anatomical structures of the human and dog ears are very similar, so it is thought that these levels will negatively impact the hearing of canines in kennels. the abr can be used to estimate the hearing threshold of dogs, and can be used to show either a temporary threshold shift or permanent threshold shift after being exposed to excessive sound levels. behavioral effects to excessive noise exposure include hiding, urinating, defecating, panting, pacing, drooling, disregard to commands, trembling, and barking. these behavioral patterns pose a much greater problem to canines than meets the eye. all of these behavioral patterns are characteristics that result in a longer stay at the kennels before being adopted. a longer stay at the shelter results in a longer duration of noise exposure and therefore more likely to show either a temporary or permanent threshold shift in the canine's hearing. these excessive noise levels are not only harming the dogs physical and psychological state, but the workers' and potential adoptive families' physical and psychological state as well. the workers' psychological state could affect the care provided to the dogs. these loud noise exposures also have the potential to reduce the amount of time that potential adoptive families spend in the facility. this can result in less dogs being adopted and more time being exposed to excessive sound levels. to reduce the level of noise exposure poses a little more difficulty because the majority of the noise is coming from the dogs (barking), but structural changes can be made to the facilities in order to reduce the noise. structural changes could include how many dogs are put in one area, more absorbing material rather than metal cages and cement walls and floors, and possibly in the future use of hearing protection devices (hpd) for the dogs. all of these structural changes would also benefit the humans involved as well as the use of hpd's (ear plugs).