Sterilization by dry heat has become increasingly popular in Great Britain. This is probably for two
reasons: first, the need to sterilize small objects,particularly syringes, and secondly, the apparatus
required is comparatively inexpensive when comparedwith the autoclave. It should also be added
that shortly after the last war autoclaves were inshort supply, and a number of people became increasingly interested in dry heat sterilization. Before considering the apparatus available it is as well to discuss the advantages and disadvantages of the method. It must be emphasized that sterilization by
dry heat depends upon the penetration of adequate heat to the article as a whole; thus it is possible to
sterilize such objects as syringes already assembled and presealed in their container, whereas steam and
gases, such as ethylene oxide, can only be relied upon to kill organisms if the steam or gas comes into direct contact with the surface of the objects. Steam, therefore, is not suitable for such equipment as assembled syringes or for articles enclosed in a sealed tube. Another advantage of this method is that objects which are damaged by water or steam, e.g., powder or ointment, can be sterilized provided the heat penetrates to all parts of the substances. The disadvantages of the method are that, first, some of the apparatus, such as hot air ovens,takes a considerable time to reach sterilizing temperature, and the
temperature and time necessary for sterilization must be considerably higher and longer than for steam. Secondly, much of the apparatus in use is unreliable and shows considerable variation in temperature during sterilization. Thirdly, the objects, particularly metal, may become oxidized at high temperatures or they may not withstand the temperature.