Determination of Lethality Rate Constants and D-Values for Bacillus atrophaeus (ATCC 9372) Spores Exposed to Dry Heat from 115°C to 170°C

Abstract Dry heat microbial reduction is the NASA-approved sterilization method to reduce the microbial bioburden on spaceflight hardware for missions with planetary protection requirements. The method involves heating the spaceflight hardware to temperatures between 104°C and 125°C for up to 50 hours, while controlling the humidity to very low values. Collection of lethality data at temperatures above 125°C and with ambient (uncontrolled) humidity conditions would establish whether any microbial reduction credit can be offered to the flight project for processes that occur at temperatures greater than 125°C. The goal of this research is to determine the survival rates of Bacillus atrophaeus (ATCC 9372) spores subjected to temperatures higher than 125°C under both dry (controlled) and room ambient humidity (36–66% relative humidity) conditions. Spores were deposited inside thin, stainless steel thermal spore exposure vessels (TSEVs) and heated under ambient or controlled humidity conditions from 115°C to ...