Risk and feasibility of aqueous solutions sterilization

Abstract

This article is intended as a basic introduction on feasibility and risks of autoclaving aqueous solutions in sealed containers. Another article, Aqueous solutions in sealed containers: internal pressure under autoclaving, provides a technical approach to the matter. The feasibility and the level of risk of autoclaving sealed containers of liquid solutions under pure saturated steam conditions (e.g. in “classical” steam autoclaves, without “counterpressure”) depends on a large amount of factors. The knowledge of the mechanical resistance of the material, of which the containers are made, is very important to ascertain whether the differential pressure shall be compensated for (and to which extent), or may not be compensated for.

Autoclaving of aqueous solutions in sealed containers: feasibility and risks

Regardless to how much containers are stressed during autoclaving, a point of an utmost importance is that containers must finally be unloaded from the autoclave into the ambient, where no counterpressure is applicable at all.
Thus, the unloading temperature is by far the most important factor to reduce the risk of fatal accidents for the operators. Both the probability of explosion of the load outside the autoclave, and the very harmful effect of the hot solutions on the human body become much smaller if the unloading temperature is reduced from 100 °C
(very high risk) to:
.80 °C (acceptable risk for small containers with filling levels lower than 80 %)
. 65 °C (acceptable risk for containers with filling levels lower than 90 %).

Filling levels higher than 90 % must always be avoided, but in the case the containers are sealed
by a movable plug and enough space is granted for the displacement of the plug during autoclaving without protruding it outside of the syringe tube (this is the typical case of pre-filled syringes). In addition to the risk of explosion during autoclaving, and to the much bigger risk of explosion during unloading operations, another
risk shall be considered. If the differential pressure is not compensated, containers sealed with stoppers might lose part of their content during autoclaving, due to the sealing being not perfectly tight, or becoming not perfectly tight at sterilization temperature.