Differences between moist heat steam sterilization and dry heat sterilization
Derek J. Prince, Ph.D.
Prince Sterilization Services, LLC
June 25, 2021
Moist heat steam and dry heat sterilization are similar in the fact that both modalities use the transfer of heat energy as the sterilizing agent. The main difference between the two forms of sterilization is how heat is transferred from the sterilization environment to the product in need of sterilization. For dry heat sterilization, heated air is in direct contact with the load items and the transfer of its thermal energy onto the load items is what results in sterilizing conditions. Dry heat induces microbial lethality primarily through the oxidation of organic compounds [1].
Where dry heat sterilization relies solely on the energy transfer of heated air, moist heat steam works by transferring the energy contained within heated and pressurized steam (saturated steam) onto the load items. Saturated steam is water vapor that is at a temperature and pressure that corresponds to the vaporization curve of water [2]. This type of steam is maintained in a state of equilibrium between condensation and evaporation, with no entrained liquid water [2, 3]. The phase change of saturated steam from gas to liquid, which occurs when the steam contacts the load items, transfers a tremendous amount of energy (2,202 kJ/kg at 121°C) onto the load items and it is this transfer of energy that allows for effective sterilization [2, 4]. Sterilization via steam is extremely fast and effective at killing a broad range of organisms, including heat resistant spores, primarily through the denaturation/coagulation of proteins. Due to its long history of success, ease of use, and its lack of toxic/carcinogenic byproducts, steam sterilization is the preferred method of sterilization for pharmaceuticals, medical devices, and health care items [5].
Table 1. Differences between Dry Heat and Moist Heat Steam Sterilization
| Dry Heat | Moist Heat Steam | |
| Sterilizing agent | Sterile heated air | Saturated steam |
| Impact of air | Used as sterilizing agent | Inhibits the sterilant |
| Temperature1 | 160-190°C [6] | 110-135°C [2] |
| Time1 | 30-120 minutes [7, 8] | 15-30 minutes |
| Biological indicators | Bacillus atrophaeous (ATCC 9372) ; others | Geobacillus stearothermophilus(ATCC 12980 or ATCC 7953), Bacillus subtilis (ATCC 5230) ; others |
| Industry acceptance | Well accepted | Well accepted, preferred method |
| Environmental impact | Air: Nontoxic, no harmful byproducts | H2O: Nontoxic, no harmful byproducts |
- Various temperature/time combinations may be used as long as proper control and rationale are documented.
Prince Sterilization Services, LLC offers contract steam and dry heat sterilization and depyrogenation services to the pharmaceutical, medical device, and related health care industries. In addition, Prince also manufacturers the SteriKit®, a pharmaceutical quality kit containing ready to use vials, seals, and stoppers. Customers may supply their own components for us to process or use components that we have in stock. Prince is FDA registered, ISO 13485:2016 certified, and cGMP compliant. Please reach out through our websites contact page or by contacting us using the link below.
www.princesterilization.com
(888) 774-6230