The gaseous products emitted in the self-heating process constitute one of the parameters suggested for detecting coal spontaneous combustion in underground mining. The objective of the study is to investigate the changes of ethylene and propylene content in a gaseous mixture which flowed through a fixed bed column filled with bituminous coal of different grain size. The mixtures of fire gases were obtained from laboratory simulated heating of coal at the temperatures of 373 K, 423 K, 473 K and 523 K. Hydrocarbons of various initial concentrations were introduced to the adsorption column at the constant flow rate of 2∙10-7 m3/s. The experimental findings show that decreasing the adsorbent granulation and gases concentration causes an extended breakthrough and coal bed saturation times. In all the tests, the saturation time was gained faster for ethylene than for propylene. Thus, the content of tested hydrocarbons, which are some of the indicators for assessing the degree of the coal self-heating process, in mine air may change in time as a result of the adsorption phenomenon. It occurs particularly at the early stage of the self-heating process and in places where coal dust has been left.