In article results of experimental researches of incrementation of attenuation in an optical fiber at deformation of loose tubes are presented. The loose tubes with 4, 8, 12 fibers made from polybutyleneterephthalate were exposed to tests. It is shown that critical value of deformation of a loose tube at which registered incrementation of attenuation exceeds threshold value of losses (0,05 dB), changes depending on the square of the area of cross section of loose tube without fibers practically under the linear principle. The received results of researches can be used for the forecast of optical cable stability to influence of crushing loadings.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.