Measurement of Equilibration Time of Dry Goods Loads in Autoclaves

Abstract

The equilibration time of an autoclave is defined as the period of time that elapses between the attainment of the sterilization temperature at the reference measurement point of the autoclave chamber and the attainment of the sterilization temperature at all measurement probes within the dry goods load placed within the autoclave during a sterilization cycle.

The equilibration time is an indicator of the ability of the autoclave to remove air from and to subsequently sterilize the dry goods load placed within the autoclave chamber. Therefore, the equilibration time is an indicator of the performance of an autoclave. Periodic measurements of the equilibration time and evaluation of the equilibration time data can assure continued performance of the autoclave.

For autoclaves that support biopharmaceutical manufacturing plants, the equilibration time is generally measured by placing heat penetration probes within the dry goods load items placed within the autoclave during a sterilization cycle. However, measurement of the equilibration time in this fashion yields results that are highly variable and difficult to replicate.

This paper presents a study that attempts to understand the impact of the following autoclave variables on the consistent measurement of the equilibration time and on the reduction of the equilibration time: type of dry goods load item placed inside the autoclave, location of the heat penetration probe placed within the dry goods load item, location of the dry goods load item inside the autoclave chamber, orientation of the dry goods load item inside the autoclave chamber, number of coils of the tubing elements of a dry goods load item, total thermal mass of the dry goods load items placed inside the autoclave, temperature of the dry goods load items at the start of the sterilization cycle, presence of residual moisture in the dry goods load items at the start of the sterilization cycle, number of steam and vacuum pulses used for preconditioning in the autoclave recipe, depth of the steam and vacuum pulses used for preconditioning in the autoclave recipe, and hold time of the steam and vacuum pulses used for preconditioning in the autoclave recipe.

The focus of this paper is on tests performed to evaluate these variables followed by analysis and interpretation of the test data to identify key variables that have the highest impact on the measurement of the equilibration time. The conclusion of this paper presents a process to achieve shorter equilibration times in autoclaves through control of the key variables identified.

LAY ABSTRACT: The equilibration time is an indicator of the performance of an autoclave. Periodic measurements of the equilibration time and evaluation of the equilibration time data of an autoclave can assure continued performance of said autoclave.

This paper presents a study performed to develop a general guideline for consistent measurement of the equilibration time of an autoclave through identification and control of key sources of variability that impact the measurement. The focus of this paper is the testing and data analysis performed to identify these key sources of variability observed in a typical autoclave load sterilized through a typical autoclave cycle in a biopharmaceutical manufacturing plant. The conclusion of this paper presents a process to achieve shorter equilibration times in autoclaves through control of the key variables identified.