Sterilizing Lumber
Definition and methods of sterilizing lumber
Question
What is the definition of sterile lumber? What are the common methods? How long does it last?
Forum Responses
There will be some variation, but it is lumber that has been heated for some length of time (several hours or longer) to 130 degrees F or higher. The wood is sterilized until it cools back down, at which point it can be reinfected if conditions are OK.
Gene Wengert, forum technical advisor
You may have heard about the new rules for softwood lumber in crates and pallets going to Europe. All softwood lumber used in crates and pallets must be marked with a stamp certifying that the center of the boards has reached 56C and been held at that temperature for at least 30 minutes. The USDA has published charts for various wood and temperatures that show how long it takes to reach 56C in the center. Inspectors will spot check your operation and they will look at procedures and you will be allowed to continue to stamp. Hardwoods are not involved yet but it appears they will be according to conventions being adopted by the United Nations. The crate wood can be sterilized by fumigation but it appears that the rules may be changed to just temperature.
Today I received a copy of heat treating standards in Australia. This process some believe could become the standard in Europe also - a minimum 74C (165F) at four hours for every inch of thickness. This temperature at the core will kill all stages of insect life. Would it really take that long? Would this also affect finish dimension? What about strength? They do not classify the wood as hard or soft, but "any timber" that is used in distribution - pallets, crates, etc.
