 Although authors estimate that at least some of the manifestations of altitude sickness may appear at elevations as low as 1 @,@ 500 – 2 @,@ 400 m ( 4 @,@ 900 – 7 @,@ 900 ft ) and it affects the fit and unfit in equal measure , its incidence is reported as lower than 1 % even at elevations of 4 @,@ 600 m ( 15 @,@ 100 ft ) and has not been reported in the Tatras . Low air pressure begins to have marginal but detectable effects at the summit ( 2 @,@ 654 @.@ 4 m ; 8 @,@ 709 ft ) . Water boils at about 91 @.@ 5 ° C ( 196 @.@ 7 ° F ) and arterial oxygen saturation is about 8 % lower than at most visitors ' places of residence , but it is difficult to distinguish slight oxygen deprivation at the summit from fatigue caused by the exertion required to reach it . Authors speak of possible minimal sensory impairment above 1 @,@ 500 m ( 4 @,@ 900 ft ) . Unlike fitness , age in itself is not a determinant factor in reaching the highest point in the Tatras . The famed Tatra guide Ján <unk> took clients to the summit of Gerlach until the age of 76 . 
