Abstract Monitoring of dangerous hydrocarbons is an important issue for both chemical process control in industry and protection of the environment. Vapors of toluene are highly dangerous in low concentrations because of its low explosive limit of 1.2 mol%. Toluene vapors in concentrations lower than the explosive limit can be detected using a fiber optic arrangement containing a short section of suspended core microstructured optical fiber (SC MOF). We prepared the SC MOF for this purpose, with an inner structure consisting of a relatively thin silica core, 2.6 μm in diameter, surrounded by three large cladding holes with radii of 26 μm, which were designed to be large enough for trouble-free analyte flow. It has been shown that a 0.3 m-long SC MOF sensing element can be used for refractometric detection of toluene vapors in low concentrations without using any other adsorption layers. We have experimentally verified the operational reversibility of the SC MOF sensing element in time. A sensitivity of 1.20 ± 0.04 dB/mol% and a detection limit of 0.0079 mol% have been determined for this sensing element. The SC MOF can detect sufficiently low concentrations of toluene vapors to reveal safety risks before the toluene reaches the lower explosive limit.