Are we consistently showing our students and colleagues good laboratory practice examples?

The fact is, with most of what we do each day, we fall back on “that’s the way it’s always been done.” And we all know that, in the long run, that’s a Bad Idea™. It’s fine to defer to habit and “just because” in the kitchen and garage. But there are a few nearly universal lab practices that aren’t just lacking in evidence of efficacy—studies have shown they are not good laboratory practice examples!

For instance, it is common practice for labs to cover empty vessels with foil during the sterilization process. But does that practice actually align with the reasoning behind it? To start with, it’s worth noting that different labs rationalize the practice differently. That’s a fairly reliable sign of folk wisdom, instead of a well-reasoned design decision. 

Although called “loose” foil covering, methods vary from lightly placed to tamped down tight. In any case, almost invariably, it actually hurts the effectiveness of the sterilization process.

How Foil Foils Sterilization 

During his tenure at California State University Fullerton, Philip Berriman tested various autoclave practices. He found that a tight foil wrap prevents the air flow that makes efficient sterilization possible, and that a loose wrap traps contaminants from the lab during the cooling process. 

What does this mean? Sterilizing flasks with foil might not be get (or keep) them sterile—the exact opposite of the stated goal of the practice!

Likewise, the common habit of sterilizing vessels vertically seems to make good practical sense. But it fails in lab testing. Berriman’s tests found that vertically positioned flasks and beakers were not always fully sterilized by the same standard autoclave cycle that effectively sterilized vessels that were autoclaved on their sides. This was especially true when it came to Erlenmeyer flasks, whose unique shape, combined with the foil cover, resulted in trapped air at the bottom that either called for a much longer cycle or resulted in an unsterilized vessel.

(Click here for more thoughts on foil and good lab practice.)

What Does the Evidence Say to Do? Good Laboratory Practice Examples 

Luckily, these problems are easily solved just by changing standard operating procedure in accordance with what the evidence shows. First, stop covering vessels with foil in the autoclave and during the cooling process. Next, when sterilizing empty vessels, lay them on their sides in the autoclave, rather than standing them vertically. There is no cost—other, perhaps, than the psychological hurdle of altering ingrained habits—to either of these changes. (In fact, using less foil might actually cost labs less.) Both are backed by science and significantly improve the efficacy of a standard sterilization cycle.