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Lab Tip: Choosing Plastic vs Metal Autoclave Trays

melted plastic bottles in autoclaves

Everyone knows they should always use autoclave trays. It’s something we at Priorclave talk about a lot. But what you might not know is that we also recommend you always choose a particular kind of tray for use in your autoclave: stainless steel, every time!

Autoclave makers advise metal containers for autoclaving loads because they’re durable and they heat up and cool down quickly. But metal trays are heavy and expensive, leading some customers to opt for the cheaper, lighter plastic bins. This is a mistake.

Firstly, plastic bins are fundamentally inefficient. This arises both from the plastic’s inherent tendency to insulate, and from the available dimensions of plastic trays, which tend to trap cold air.  Some labs address this by adding water to the tub, which both increases the “thermal inertia” of the load (as well as creating some burn risks for the operator).

According to Priorclave’s Lee Oakley, “loads like these are going to take longer to heat up and then retain the heat, so it takes longer to cool down.” All else aside, they slow down lab operations. In all likelihood, even running just a few cycles per week, the time savings would more than pay for decent steel trays in short order.

Plastic Bins Can Be Dangerous

But convenience isn’t the only, or even the most important, factor. Safety is the #1 reason we recommend against plastic trays. That same tendency to insulate doesn’t just slow down operations. It also means that the contents of the tray, in addition to the tray itself, can be much hotter than expected. Temperature surprises are especially unwelcome in the lab, where they can lead to spills and scalding, and contribute to ruptured bottles and even “bottle bombs.”.

And it’s not just the temperature that could be an unwelcome surprise: plastic’s long-term durability is often unknown and unknowable—resulting in unexpected and often abrupt failures after repeated heat/pressure exposure over time. This is a common accident scenario: a plastic tub, bin, or tray containing media bottles looks fine, and then abruptly buckles under the weight of the water and load when the lab tech goes to remove the load from the chamber, drenching them in near-boiling water and liquid media. While the greatest risk obviously comes with using low-quality tubs (like those found in a hardware or superstore), this has even been recorded in labs using high-quality high-density polyethylene tubs intended for lab use.  

Priorclave always keeps safe and efficient lab operations front and center.  A few small adjustments—like which trays you choose!—can help you maximise autoclave safety and minimise accidents in your lab.