A method for determination of main parameters of a meteoroid at the height of its maximum deceleration is proposed. It is shown that the largest meteoroid reaching the height of maximum deceleration and producing a thermal explosion in Earth's atmosphere has a mass of approximately 10⁹ g. The largest annual meteoroid running into Earth has a mass of 7⋅10⁸ g. An analysis of results obtained from observations of flashes in the atmosphere of the Earth by means of geostationary satellites of USA is carried out. It is shown that the meteoroids for which the energy of flashes exceeds 20 kt TNT are borned by comet bodies. Using our method and improved data on the Tungusskiy phenomenon, we showed that it was not possible to explain the phenomenon within the framework of model of monolithic body. A Tungusskiy event occurs once every 1300 years. We expect that an explosion of the meteoroid in the atmosphere occurs when a body reaches the height of maximum deceleration. For this height, we calculated absolute magnitudes of flashes and their temperatures for some selected fireballs.