Dry Heat Sterilization (or Depyrogenation) is a process aimed at the reduction in the level of pyrogens with the use of hot air in temperature ranges from 160°C up to 400°C. The temperature used depends on the duration of the process. There are two types of heat convection that can be used; gravity or mechanical. The former uses the natural interaction between air of different temperatures, and the later produces a specific flow of air with the help of a blower.
Depyrogenation is mainly used in the sterilization of vials for aseptic filling. The process is also useful to sterilize assembled and packed materials, since heat conduction does not require the contact of the product with steam or water. However, not all products can withstand the high temperatures required for this kind of process (eg. metal goods, heat sensitive solutions, etc).
There are two main techniques of depyrogenation; batch and dynamic. Batch form is usually done in static ovens where the product is placed in metal crates and exposed to high temperatures. Dynamic techniques involve the use of a depyrogenation tunnel, where goods are transported over a continuous band through the different heating zones of the tunnel.