Temperature profiles and sterilization within a dead-ended tube.

Use of steam-in-place (SIP) sterilization has increased as the complexity of biotechnology processing equipment has increased. Extensive biological testing is required prior to use of this equipment as no quantitative guidelines exist for the design of SIP sterilizable equipment. Dead-ended geometries present the most difficult challenge to SIP sterilization, but data are not available as to the effects of tube orientation, length and diameter on time required for sterilization. This study examines the effects on sterilization of location within a dead-ended tube and orientation of the tube with respect to the gravitational vector. Temperature profiles and biological kill of Bacillus stearothermophilus were determined for four tube orientations. Kill kinetics were characterized by time to start of kill and cycle log reduction (CLR) times. Both values increased with increasing distance up the tube and orientation of the tube in a more horizontal position. CLR values were as much as ten times greater than those resulting from saturated steam. Projected sterilization times were determined and found to be very dependent on tube orientation. Recommendations are given for sterilization and validation testing of dead-ended geometries.