A “wet pack” is any load that comes out of the autoclave problematically damp. The term originates in medical settings, where it usually referred to wrapped instruments that had visible moisture on or inside the pack after sterilization.

Wet packs are a huge headache for a hospital’s sterile services department and a chronic issue in dental offices or medical clinics. This is because any moisture can create a pathway for microorganisms to contaminate hypothetically sterile items. In a medical setting, no wet pack can be trusted, and every wet pack should be treated as a serious red flag.

In most research and industrial labs, wet packs are of less concern. That said, consistently wet loads are still an inconvenience, and can threaten the validity of research or testing.

In most labs, annoying wet loads can usually be traced back to one or more of these three common causes:

1. Improper loading: Good sterilization requires good steam circulation in the autoclave chamber. Just as overloading can trap cold air pockets, it can also trap steam. That steam will condense and pool in the load, rather than draining away at the end of the cycle
2. Autoclave issues: This includes problems with the sterilizer itself (e.g., poor steam quality—especially in systems relying on house steam or an external steam generator—or malfunctioning drains and vents) and with the programming (e.g., incorrect settings when running the cycle)
3. Incorrect handling: Opening the autoclave too soon or unloading items before they have had adequate time to cool will encourage condensation to form on the load

With a little care, you’ll find it pretty easy to avoid wet packs and produce drier loads in the lab.

How to Avoid Wet Packs in the Lab

There are four things any autoclave user can do to ensure they end up with the driest possible finished loads:

1. 1. Load Carefully: Always load your autoclave with an eye toward steam and air circulation and keeping vents and drains clear.
   2. Choose the Right Cycle: Make sure you are running a cycle with a “post-cycle vacuum” stage. This evacuates the chamber at the end of the cycle, taking a great deal of residual moisture with it, and speeding evaporation. (That said, for a vacuum alone canot reliably result in completely dry loads. For that you need to apply additional heat to the chamber at the end of the cycle, usually via an integrated external heat jacket or heater mats.) Warning: vacuum cycles are strictly for non-liquid loads. If you pull a post-cycle vacuum on flasks holding liquid media, they’ll likely boil over or burst.)

• Perform Regular Maintenance: Wet loads are generally the result of steam lingering too long in a cooling chamber. The culprit is often a partially obstructed drain or vent. Regular maintenance will prevent that from becoming a problem. If the maintenance schedule looks daunting, follow the advice of lab instructional support tech Kelly McVey. Want to stay one step ahead of trouble? Performing a regular Bowie-Dick test. Also known as a “dynamic air removal test,” this will confirm that your sterilizer is properly pulling and holding a vacuum, and thus can effectively clear steam from the chamber at end of cycle.

1. Dry and Store Sterilized Items Properly: A load of lab glassware fresh out of the autoclave is like a load of dishes fresh out of the dishwasher: items are hot, and likely have trapped some moist air (especially in narrow-mouthed flasks or long narrow tubes). Tightly stacking or packing these items in sealed cupboards can lead to condensation, potentially creating an environment for microbes to colonize. A lab drying cabinet can be extremely useful if you don’t have the luxury of allowing loads to fully dry before unloading the autoclave.

Optimize Lab Efficiency with Priorclave

Budgets are tight, and resources are valuable. The last thing you need is to waste time, water, and electricity re-running sterilization cycles. At Priorclave, our goal is to make sure labs of all sorts run as smoothly as possible. That means lab techs can spend more time doing their work, and less time pampering their equipment. We build each autoclave to order, ensuring it has the right combination of features to help you get the job done with as little hassle as possible. Get in touch whenever you’re ready to discuss what combination of features will serve you best.