USDA heat treat requirment

[Eppdso]

So i don't thing this is a very talked about subject but where do all of you stand on the USDA requirement to heat treat wood that will be transported out of a quarantined area? I ask this when it comes to the drying of lumber and slabs and the effect that it would have on them to reach the required 160 degrees for 75 minutes. Will it dry them out to fast or will it not cause an issue?

[Southside]

Where did you get those numbers?  It's been a while but last I knew the APHIS time at temperature requirements were based on thickness and core temp of 137 if I remember correctly?  

[scsmith42]

Where did you get those numbers?  It's been a while but last I knew the APHIS time at temperature requirements were based on thickness and core temp of 137 if I remember correctly?  

The older USDA manuals specified 133F.

[Southside]

Ok. Maybe we set for 137 to make sure the line didn't drop below the minimum. It's been a decade.  Do you know if it's still the same?

I don't think I would want to bring green wood up to that temperature without the gradual step increase seen in a kiln schedule.

[scsmith42]

Chapter 7, page 146 of the USDA AH-188 Dry Kiln Operators Manual (2001) address sterilizing for insects and mold. Table 7-31 on page 176 provides a schedule for killing powderpost beetles and their eggs based upon three different temps (125, 130 and 140) and three different wet bulb depressions.

10 hours for 4/4 at 60% RH at 130 per the manual.

Higher MC% requires higher temps to sterilize.

[GeneWengert-WoodDoc]

Appreciate that AH-188 was written 70 years ago and the suggestions were based on research done in England.  Further, the standard idea was that an internal temperature around 130 F was adequate, but today it has been changed to no less than 133 F throughout.  When injecting steam to achieve the WB of AH-188, the steam, when it condenses on the wood, is actually above 212 F, so the wood gets really hot. So, this is why today we use different guidelines.

The control of WB temperature when sterilizing today is no longer a consideration, but with wet wood, the wood's temperature is closer to the WB temperature than to the DB, so WB is indeed important.  Of course, in a tight chamber with live steam injection, the WB will be close to the DB.  Finally, today we are concerned more about other insects, and not so much about the lyctid PPB, so the lyctid procedures are no longer valid.

With commercial sterilization, there is a third party certification which allows the treated wood to be stamped that it has been sterilized.  This is required for lumber, logs, dunnage, undried wood, and many other wood products being exported.

As the lyctid PPB likes drier wood, there is no guarantee that sterilized wood is free of the insect in the future...it can be exposed and infected during storage in a warehouse containing infected wood or even bamboo.