Wet Packs: A Quick Guide on How to Prevent a Common Problem in Sterilization

CSS_Scott Mechler_Headshot
Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

One of the worst things you will encounter after running a sterilization cycle in your autoclave is evidence of moisture within the chamber or within the load itself. This phenomenon, known as wet packs, may not seem overly concerning but should be taken seriously and investigated. A wet pack is a sign that something is potentially wrong with your equipment, your process, or your building utilities and it should to be corrected and eliminated immediately.

A wet pack can cause contamination issues because excessive moisture can act as a pathway for microorganisms. This can lead to re-contaminating your sterilized load. In others words, if a load such as surgical instruments or pipette tips is not properly dried then microorganisms may wick through the wrapping and deposit themselves on the sterile load.

Why Do Wet Packs Occur?

A wet pack can occur for any number of reasons. There is no single place to look first. There are, however, certain operator behaviors and processes as well as mechanical failures within an autoclave that could lead to the moisture being retained inside an autoclave chamber and/or load.

Each of these things, either on there own or collectively, can lead to a wet pack. The trick is knowing what to look for.

  • Operator Error – Operators who are not trained correctly, or lack thorough training within a laboratory setting, are a common cause of wet packs. This happens because an operator has either loaded the autoclave with too much material (think density), selected the wrong sterilization cycle, or they have improperly handled the load in some way prior to placing it in the sterilizer or after a sterilization cycle is complete.

    • Do not over pack the autoclave and do not cover the chamber drain.
    • Ensure there is plenty of space for steam to travel around the load and into the drain.
    • Verify that the correct cycle is selected with the proper amount of dry time.
  • Component Failure – A wet pack in your autoclave could mean there is something physically wrong with the autoclave itself. Components that can cause wet packs include valves, steam traps, vacuum systems, and chamber drain strainers.

    • Check all steam traps on the autoclave and/or the main steam line to the autoclave (if applicable).
    • Check and clean the chamber drain strainer.
    • Make sure the vacuum system is functioning and pulling a deep vacuum at the end of the cycle.
  • Steam Supply Issues – If your autoclave is fed with “house steam”, check that the incoming lines are insulated and properly trapped. You could have a steam trap on the main steam line to the autoclave that is clogged or not properly flowing with saturated, dry steam. This can lead to your load becoming waterlogged from too much condensate.

    • A steam trap inspection program should extend beyond the sterilizer to include all of the traps back to the boiler.
    • Ensure the autoclave is fed saturated steam with acceptable dryness and particulate levels.
  • Improper Storage – Once you take your load out of the autoclave how do you store it? A load that comes straight out of the sterilizer is often hot and typically holds a small amount of moisture. Problems can occur when you go to store your load, and proceed to stack it on top of another like you would a piles of books—thus creating a pocket that could lead to potential build up of moisture and hence a wet pack.

What to do when noticing a wet pack

The immediate response should be to halt any further loads for that particular sterilizer and search out and solve the underlying issue with the help of a seasoned service technician. A service technician should have the knowledge and experience to know how to troubleshoot the problem. A service technician can also help determine what maintenance or training is needed to ensure wet packs are less frequent or nonexistent altogether. They may also suggest further preventative maintenance.

Download our free eBook to learn how to properly maintain your autoclave >


One of the best ways to prevent wet packs is to develop a daily routine to ensure all processes are on point and equipment is in good working order. Developing a good working relationship with a service technician is also a good idea because they will in turn educate operators on what to look for to ensure wet packs don’t occur again.

Lastly, if you are experience wet packs for the first time ask yourself the following questions:

  • Did any new users use the autoclave recently?
  • Were the sterilization cycle parameters (time, temp, dry time, etc) modified in any way?
  • Was the load properly packed during the last cycle?
  • Did the facility lose power and/or steam supply recently?
  • Did something change in the way the load was prepared or processed?

Please contact us with any inquires or if you would like more information. Our service technicians are well versed in how to diagnose and fix issues that lead to wet packs.

Protect Your Investment

Preventative and proactive maintenance are the keys to reducing downtime and ensuring the longevity of your autoclave. Read this eBook to learn how to properly maintain your autoclave and develop a comprehensive maintenance plan.

Get the Free eBook
Protect Your Investment