EO Concentration
- Commonly 400 and 700 mg/l
- As EO concentration increases at a given temp and RH,
–microbial inactivation (kill) rate increases - Killing concentration required at the site where the microbes (BI’s) are located
Water Vapor (Humidity)
Required for EO to react with the critical cell molecules
• Generally measured as Relative Humidity
Temperature
- Kill rate increases with temperature
–D-value decreases (time) with temperature
–Exponential function - For each 10°C (18°F) rise in temperature, the spore inactivation rate will generally double
Time
- Amount of kill increases with exposure (EO gas dwell) time
- 90 percent of surviving microbes are killed for each D-value time in gas dwell
D Value ?
- Determined to prove predictable logarithmic death kinetics of challenge microorganisms (BIs) or natural bioburden
- “Decimal” Reduction Time – Measure of the biological organism’s resistance to the sterilant
- Time in minutes necessary to reduce (kill) a microbial population by one logarithm or 90%