To accurately guide the quantitative injection of carbon dioxide for extinguishing the fire or diluting the accumulated toxic gases, 26 sensing devices used for detecting the multiple environmental parameters were firstly laid inside and outside of 210 m(3) large sealed space, then each signal output from the sensing devices was transmitted successively to the A/D conversion module and the server with signal acquisition and analysis software, so the experimental research on inerting characteristics of carbon dioxide in different physical forms in this sealed space were carried out by using the mobile liquid storage and injection equipment, including fire source extinction, and accumulation and distribution of gas components, as well as cooling. Results show that: (1) For wood and gasoline, the critical oxygen concentration of combustion 16.98 % and the corresponding carbon dioxide concentration 28.6 % were determined comprehensively; (2) The concentration layering law in the stabilized gas was proved to be inconsistent with theoretical correspondence between specific gravity and height; (3) For direct liquid injection and gas perfusion at 2.2 MPa, the average temperature difference were 13.8 degrees C and 0.3 degrees C respectively, so the temperature drop characteristic of liquid injection was proved, and its optimal cooling distance from the nozzle is further determined from 5.6 m to 11.2 m. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.