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Sterile Storage – An Assessment of Temperature and Humidity Conditions


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Sterile storage is intended for storing and preserving the sterility of sterile items. In the 1990's event-related sterility became the norm in hospitals in the United States. Previously, time-related sterility was used, whereas a product outdates based on a date-related process. However, in the mid-2000s the FDA revised the 510k process changing the shelf life requirements.

Sterile Storage Temperature and Humidity Guidelines


The current ASHRAE Standard 170 guidelines specify a maximum temperature of 75°F and a maximum relative humidity of 60% for sterile storage. Past ASHRAE 170 Standards listed temperature ranges as 72 degrees F to 78 degrees F. In the AAMI ST 79: 2017 guidelines, temperature, and humidity recommendations were removed in favor of the ASHRAE standards. There are continuing evaluations of how both temperature and humidity affect sterile packages. Standards are applied for the period of construction of the area. To know what standards apply to your facility, you will need to know when it was built or renovated last. The Facilities or Building Services department should be able to supply the date and the Facility Guidelines Institute (FGI) guidelines, which refer to ASHRAE, that were applied at that time.

Sterile Storage Temperature and Humidity Deviations


Whether a product has an event-related or time-related shelf life various factors, referred to as "events," can play a role in contaminating sterile packages. Temperature and humidity are frequently cited as key factors in contamination among these elements. When temperature and humidity levels go outside the normal range, there are some important considerations to take into account. When evaluating environmental conditions and potential contaminants in sterile storage areas, The Joint Commission notes, "A small deviation for a brief duration may not be clinically significant, whereas a large deviation for an extended period may have clinical implications." In my previous reviews of Instructions for Use (IFUs) for sterile packages and packaging, I noticed that manufacturers commonly recommended storage temperatures between 59 degrees F to around 86 degrees F. However, some manufacturers also included a note that the products may be temporarily stored outside of this temperature range for short durations. I have reached out to numerous manufacturers to define a short time frame, but unfortunately, none were able to do so.


Although not considered best practice by ASHRAE, the IFUs of many sterile packaging products used in hospital sterile processing departments almost always list humidity storage ranges at 30%-60%. Hospitals often have issues with maintaining this humidity range throughout the seasonal changes in the U.S. Understanding that humidity is relative to temperature, and the higher the temperature, the more water vapor can be held in the air. A risk assessment should be conducted when deviations from your standard persist for extended periods or when excursions are significant. A visual risk assessment is a helpful tool for evaluating the atmosphere and existing conditions. It allows us to assess the dew point, looking for water droplets on the walls and storage shelves, which would indicate a significant change. At that time, if the humidity reaches the dew point, a risk assessment needs to be conducted for each package, along with an evaluation of how long the conditions persisted. Another more reliable process is using a thermometer and hygrometer to measure temperature and humidity. With the use of a thermometer and hygrometer, we can detect the growing atmospheric concern in sterile storage and react sooner than the dew point.


Development of a Temperature and Humidity Excursion Risk Assessment

One recommendation on how to develop a risk assessment for a temperature and humidity event can be found in a white paper by ASHRAE titled "Humidity Control Events in Perioperative Care Areas." The Canadian Standards Association also created a consensus statement regarding " High Relative Humidity in Sterile Storage Areas," which outlines their recommendations for reaction points. Theories differentiate as to when to react, which can vary from a humidity point of 70% to a reaction point of a percentage of your set point.


Other global publications have indicated that commercially manufactured products can withstand more considerable variances than products produced within the CSSD departments. Indications for storage issues point to the fact that events are more likely to cause contamination than time. However, time is still an event, and deterioration of the packaging can occur and will occur at some point based on sterile storage conditions. Deterioration can be increased by temperature and humidity conditions depending on the packaging. Recommended articles for reading to advance your understanding of this complex process are:

Specifications for temperature and humidity in sterile storage environments – Where's the evidence?

Temperature and humidity in the storage area of sterile materials: a literature review Bruna CQM, Graziano

Temperature and Humidity - Monitoring Requirements for Sterile Supply Storage Areas

The Joint Commission

Lastly, the FDA requires the manufacturers to place an expiration date on all products requesting a 510k clearance. They must also list the sterile storage conditions. Most manufacturers don't test their products for sterility for much more than six months to a year, with only a few going the extra mile for a couple of years or more. To prioritize patient safety, despite the increasing evidence from the past three decades in favor of event-related sterilization, we are unable to assess the performance of one product over another without a laboratory test for contamination. Therefore, it is essential to establish protocols for temperature and humidity deviations grounded in scientific data and guidance provided by product manufacturers. Additionally, we must define standards for handling products during these crucial periods. Without proper protocols, we have no way of assuring our sterile products are safe.



To keep current on topics related to sterile processing and infection control visit our news page. https://www.evolvedsterileprocessing.com/news



At Evolved Sterile Processing, our consultants have a greater focus on sterile processing. With our decades of experience, we will help you develop better processes and educational resources for your staff.


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