When we last discussed red-bag waste autoclave procedure, we talked about running “your standard waste cycle” (noting that these vary by lab).

So how do you determine your lab’s “standard” biohazard waste cycle?  The general rule for autoclave sterilization taught at most colleges is “15 minutes at 121ºC kills everything.“  But that’s definitely too short a cycle time for bagged waste, because the bag drastically slows steam penetration.

Googling isn’t much of a help.  A quick search reveals a huge variety of “standard” biohazard waste cycles:

• Most U.S. universities currently favor 30 minutes at 121ºC for bagged biohazard waste loads…
• but the U.S EPA seems to recommend 60 minutes at 121ºC for “TRASH” loads…
• while the CDC goes much longer, offering this example—”the decontamination of 10 lbs of microbiological waste … requires at least 45 minutes at 121°C because the entrapped air remaining in a load of waste greatly retards steam permeation and heating efficiency”—and further noting: “If steam sterilization … is used for waste treatment, exposure of the waste for up to 90 minutes at 250°F (121°C) in a autoclave (depending on the size of the load and type container) may be necessary to ensure an adequate decontamination cycle.”   

Finally, in the UK–where Priorclave manufactures autoclaves–the common practice is to double-bag waste, add water before closing the bags (to aid steam saturation), and run bagged biohazard waste for 30 minutes at 126ºC in an autoclave outfitted with both a pre-cycle vacuum stage and pulsed freesteaming.  The vacuum stage and pulsed freesteaming both improve steam penetration.  And, all else being equal, raising the load temperature by 3ºC will cut cycle times in half, provided there is ideal steam penetration.

In summary:

Your biohazard waste cycle time should be longer than 15 minutes, but probably under two hours, and at least 121ºC. Evacuating air from the chamber before the cycle, and pulsing the steam as you fill the chamber, will both shorten the cycle and increase efficacy.

Obviously, “15 minutes to two hours at more than 121º” is pretty vague.  You probably want to narrow that down.

How to Determine the Right Biohazard Waste Autoclave Cycle Time for Your Lab

According to Tony Collins, Managing Director of Priorclave, Ltd., “The only real way to tell is by doing performance testing to see what is actually going on inside the load.”

A “performance tests” uses logged temperature probes to track temperature changes throughout a load over the course of a given cycle.

In order to perform a biohazard waste processing performance test:  Prepare a biohazard load, placing temperature probes throughout the load. Then, run that load  through a long sterilizing time (such as the CDC-recommended 90-minute cycle at 121ºC).

“By looking at the plotted results from the probes, you can see how long it takes for all of the load to hit the sterilizing temperature.”

You then use those data to guide what you consider the appropriate sterilization time and temperature for biohazard loads in your lab.