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Sterile Storage – An Assessment of Temperature and Humidity Conditions

Updated: Mar 10, 2022

It is stating the obvious, that sterile storage is designed to store and maintain the sterility of sterile items. However, event-related vs. time-related dating of sterile items is becoming a topic of discussion again. How long an item can maintain sterility is still being researched. There are many contributing factors, often called "events," that contribute to the contamination of sterile packages. One of the most frequently spoken about contributing factors for contamination is temperature and humidity.

Guidelines from the current ASHRAE Standard 170 lists a temperature rating for sterile storage not to exceed 75 degrees F and a relative humidity rating not to exceed 60%. 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. For you 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.

When temperature and humidity excursions happen, there are a few considerations you must make. To start, when making an assessment for environmental conditions and possible contaminates in the sterile storage areas the Joint Commission comments, "a small variance for a short period of time may not be of clinical concern, whereas a large variance for a longer period of time may have clinical significance." Water vapor may be much more a threat to sterility than temperature, also understanding that humidity is relative to temperature, and the higher the temperature, the more water vapor can be held in the air. In my past reviews of IFU’s for sterile packages and packaging, the manufacturers listed a common theme of storage ranges from around 59 degrees F to approximately 86 degrees F with a caveat listed as "may be out of range for short durations." I have reached out too many manufacturers to define a short duration, and unfortunately, none would. Most sterile storage areas fall within that specified temperature range, although not being best practice as defined by ASHRAE. Humidity ranges in the IFU’s almost always were listed at 30%-60%. Hospitals often have issues with maintaining this humidity range throughout the seasonal changes in the U.S. A risk assessment needs to occur when deviations in your standard last for prolonged periods of time or when excursions are dramatic in nature. A visual risk assessment is one of the tools we can use when evaluating the atmosphere and existing conditions. A visual assessment allows us to assess the dew point, in the way of water droplets on the walls and storage shelves, which would be considered a dramatic change. At that time, in the case of humidity reaching dew point, a risk assessment of every package needs to occur, and an evaluation of how long the conditions existed does too. The other, 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. So, where do we go from here?

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, and deterioration can be increased by temperature and humidity conditions depending on 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?

TerryMcAuleyMSc (Medical Device Decontamination) (current), Grad Dip Education and Training

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

Rev Esc Enferm USP 2012; 46(5):1212-7

Temperature and Humidity - Monitoring Requirements for Sterile Supply Storage Areas

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 of a couple of years or more. In the name of patient safety, even with the growing documentation of the last thirty years supporting event-related sterilization, we cannot determine on our own how one product is performing over another during an event without a laboratory test for contamination. So, we must create protocols for temperature and humidity excursions based on scientific data and recommendations from the manufacturers of the products we use and create standards of how to handle products during these critical times.

To keep current on topics related to sterile processing and infection control visit our news page.

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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