Simplified and insensitive to ambient condition mechanical bi-directional fiber-optic switch that can work in fire and explosion hazardous environment. The switch houses a sensitive element--a length of single-mode optic fiber and a bending device, which being activated provides specific bending of the optic fiber that introduces high attenuation of an optic signal so completely terminating light signal transmission. The switch can be configured as single on/off switch or multi-channel one.