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Archive for November 13th, 2010

Bed Bugs: Thermal Kill

Although pesticides generally don’t work against bed bugs, the critters seem surprisingly susceptible to overheating, with the Australian CoP (references in the first post) noting:

Bed bugs are very sensitive to heat and are rapidly killed when exposed to temperatures over 45°C.

In the US, the equivalent 113°F seems to be regarded as a three-significant-figure Golden Number; I’ve even seen similar temperatures with a few digits trailing a decimal point.

In round numbers, you want to heat objects to an interior temperature of at least 120°F and hold them there for perhaps an hour to ensure the bed bugs get the message. The CoP observes:

It is often claimed that bed bugs can be killed via heat by placing infested materials into black plastic bags and then into the sun. However, a scientific investigation has shown that this can be ineffective with large items such as mattresses, which have a high thermal inertia

Our infestation began during late July and early August, with clear skies and high temperatures. Our house has an easily accessible attic that becomes unbearably hot on sunny summer days. We have also learned to park the van so the huge windshield isn’t aimed at the afternoon sun.

Plus, I’m the sort of bear who has a RayTek (now Fluke) IR emission thermometer, a Fluke 52 dual thermocouple thermometer, and some Onset dataloggers. Maybe we can make this work…

The attic air temperatures in August were, at best, marginal, according to a data logger tucked into gel packs inside a foam box, with an external sensor dangling in mid-air:

Attic temperatures

Attic temperatures

While the air temperatures got over 120°F, that didn’t necessarily mean the contents of the canonical black plastic trash bags would heat up. We did put most of our clothing (in bags) and small items in the attic, moving them there at the peak of the temperature curve, simply to get them out of the house. The peak inside-the-bag temperatures, according to  the IR thermometer, generally exceeded 120°F, so we felt comfortable leaving the bags up there.

The van became our main killing machine. The same logger produced this record; obviously, location and weather dramatically affect the interior air temperature.

Van Temperatures

Van Temperatures

Although the air temperature rarely got above 120, the temperature in the inner layers of clothing inside black plastic bags laid on the dashboard & seats under the sun routinely exceeded 130°F, as measured by the IR thermometer.

Our electric clothes dryer reaches 150°F on the High setting, so we began toasting all our clothing in there. The hot water supply simply isn’t hot enough to matter, so we continued to use the washer’s Warm/Cold setting.

We had been considering getting a chest-style freezer to preserve Mary’s garden harvest and this note in the CoP pushed us over the edge:

If the freezer is operating at or around -20°C, then two hours at this temperature will kill all stages.

The American translation is -4°F, which rounds off to zero. A logger tucked into the freezer confirms that the default thermostat setting of 4 should suffice:

Freezer temperatures

Freezer temperatures

A closer look shows a classic bang-bang thermostat in action, with pretty nearly a 50% duty cycle. The period got longer as we filled the freezer with veggies and similar dense materials.

Freezer temperatures - detail

Freezer temperatures - detail

The freezer disinsected items we didn’t want to (or couldn’t) toast: keyboards, mice, trackballs, notebooks, purses-with-contents, and so forth.

Between the attic, the van, and the freezer, we had sufficient weaponry to make some headway. Remember that we had a small infestation, just a few bugs, and were not trying to disinsect the whole house and all our belongings.

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