29 Sep Using the house hold oven as a heat sterilizer

As a contractor specializing in heat sterilizing belongings I have found the most useful temperatures to be between 140f and 155f. Anything lower than 140f and there are risks of not attaining core temperatures of 122f in a reasonable amount of time and there is no room for error. At 158f and beyond the risks of damage to belongings grow rapidly. As an example another heat sterilizer was experimenting with heating a dresser with input of 185f and found the dresser was, and I quote, “utterly destroyed.” Slightly lower temperatures around 160f consistently take the glued veneer edges off a cheap particle board dresser.

Over the years we have heat sterilized hundreds of loads of belongings with books (heated at 140f to 150f) being a common item. The important part in heating books at these temperatures is to leave them in the closed position until they cool off. The glue bindings become very soft with heat and need to harden before being opened. The books are, with some exceptions, just fine after treatment. But sometimes we bring home a book from the library and, after I do mandatory inspections, find any black spotting insist that the book be heat sterilized. But I don’t want to start the trailer for such a small thing so I started using the household oven. We have had some success and some failure with this tool.

Generally speaking our oven has not damaged a whole lot of books but the damage is much higher than the results I get from my trailer which can be adjusted very carefully for temperature. The biggest problem we had was forgetting the books in the oven overnight and my wife preheated the oven for pizza the next day and found the forgotten books were charred and the kitchen smokey. We had to buy those books from the library as they were destroyed.

To ascertain exactly how the oven functioned as a heat sterilizer I decided to do some experiments. I placed a temperature probe in the oven and attached it to my “Electrotherm model TRH670A” electronic thermometer. This device is about 10 years old and I had it NIST certified in 2008 at plus/minus 0.1f for accuracy. The oven is a GE brand model number JCBP40D P1WW. This is a 30 inch stove with convection capability but used the standard bake feature for the experiment. The probe was located in the middle of the stove near the bottom rack. I set the oven on the lowest possible setting which is 170f. The following are the results:

 

8:08am 69f

8:10am 93.7f

8:15am 227f

8:17am 230.9f (high point)

8:20am 227.2f

8:25am 216.9f

8:35am 194.6f

8:40am 185.5f

8:45am 177.4f

9:00am 158.7f

9:05am 153.3f

9:10am 149.0f

9:14.5am 145.5f (low point and the element kicked on again)

9:22am 178.9f (high point before the temperature starting going down)

9:24am (placed two books into oven each with a probe in the middle of the book)

9:35am 152.3f

9:40am 147.2f

9:45am 143.6f

9:50am 184.8f

9:51am 185.5f

9:54am (removed books from oven)

 

What is immediately clear is that it is vital to preheat the oven as the temperature hit 230.9f which is ridiculously hot for heat sterilizing. The damage potential is very high at these temperatures. As such preheating and allowing the oven to drop temperatures for about half an hour is important. Even after preheating the temperatures varied between 143.6f and 185.5f at the extreme ends of the heating cycles – very hot.

 

The following are the temperatures (each book had its own probe) recorded in the books:

 

book 1: Understanding Wood Finishing by Bob Flexner, Readers Digest Association, 1999. (measures 11 inches tall by 8.5 inches wide by ¾ inch thick.

 

9:24am 69f

9:30am 91.5f

9:40am115.4f

9:45am 121f

9:50am 131.4f

9:54am 142.7f (book removed from oven after exactly half an hour of heating)

 

Book 2: The Autobiography of Malcolm X by Alex Haley, Ballantine books, 1992. (measures 7 inches tall by 4.25 inches wide by 1.125 inches thick)

 

9:24am 69f

9:30am 98f

9:40am116f

9:45am 120.9f

9:50am 131.3f

9:54am 139.1f (book removed from oven after exactly half an hour of heating)

 

The probe tips were placed in the exact center of the books. The Malcolm X book had the tail end of the metal probe sticking out of the book to make sure the tip was in the center. This may have had some bearing on why the temperature was so high at 9:30am compared to the other book. Toward the end the temperatures evened out a bit. Also the recorded temperatures are not exact as it took a few seconds to switch probes on the electrotherm. The temperatures were rising quickly and I could not get exact measurements at exactly the correct time listed – but they are very close.

We can see here that half an hour of heating the books in a preheated oven was more than adequate to heat sterilize these books. The books, after cooling, appear to be in perfect condition.

This is not to say that every book would heat with the same characteristics. For example a large dictionary would probably heat slower. To compensate for differences, and to add a level of redundancy, we normally heat our books for 1 hour before removal. Also different ovens heat with different temperatures. Overall the household oven is considered the sledgehammer of bed bug heating – it works but it can only be used on heat resistant items. Electronics, even on the lowest setting would be utterly destroyed in the oven.

disclaimer:  the house hold oven is not designed to heat sterilize books and there is risk of fire if not used carefully.    I think oven manufacturers should make  bed bug heating option (at exactly 140f)  in the same way they have a locked out self cleaning option.  This would be infinitely better than a pack tite suit case heater.