A gas explosion is the severest threat to the safety of coal mines, particularly in highlands. For effectively preventing gas explosions in coal mines, a quartz tube–based gas explosion test system with an open end and a nearly spherically confined gas explosion testing device were devised, fabricated, and tested. The suppressive effects of aerosols, here silicone dioxide (SiO2) and diatomite powder aerosols, of various sizes on mine gas explosions were studied. Scanning electron microscopy, low temperature nitrogen adsorption, and thermogravimetry analysis conducted on diatomite showed the porosity, effective specific surface area, adsorbability, and excellent thermal stabilities of the aerosols. Explosion suppression experiments confirmed that a test system of SiO2 and diatomite powder aerosols remarkably prolonged the gas explosion induction period and the time of peak explosion pressure and reduced the flame propagation rate. In addition, the test system reduced the maximum explosion pressure and maximum and average explosion overpressure rising rates. The suppressive effects were clearly affected by the aerosol type and size. Microscale diatomite powder aerosol exhibited a stronger suppressive effect than microscale SiO2 powder aerosol did. The porous structure and thermal characteristics of diatomite powder was vital in the suppression efficacy because they restrained the growth rate and activity of free radicals obtained through explosion reactions and eventually eliminated them. The adsorption of formaldehyde, a major intermediary of gas explosion, by diatomite powder decreased the quantity of free radicals, eventually suppressing explosions.