Vacuum fumigation is a modern technique of disinfection of library materials which is essential in a tropical country such as India. In this process, poisonous fumes enter into an evacuated high-pressure-proof steel chamber through a volatizer. The poisonous fumes enter the body of insects through the spirade, ostium, and other openings of the insect during breathing, and directly affect the respiratory system. Experiments to ascertain the lethal dose of ethylene oxide and carbon dioxide (1:9) for different stages of the insect life cycle were conducted, and the results are discussed.