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Stickers Are Not a Legitimate HT Mark
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The American Lumber Standard Committee has stated that the HT mark on lumber must be an indelible and unremovable mark. Having said this, the use of stickers as the only means to identify lumber as HT is not considered a legitimate heat treatment mark. It can be employed as a secondary method for the benefit of the buyer of the lumber but cannot be used by an agency as verification of being heat treated. The treating facility should mark the heat treated lumber using ink or some other indelible and unremovable marking in order to meet ALSC regulations.
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Probe Placement Related to Wood Thickness
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To monitor temperatures throughout the heat treatment cycle, one of the options ALSC Wood Packaging Material Enforcement Regulations offers in section 8.b.iii states,
"direct measurement of wood core temperature in the thickest piece(s) by use of thermocouple(s) properly sealed with non-conductive material."
ALSC has clarified that if two deck boards or stringers are abutted to where no air flow can move between them, these pieces are combined and considered the thickest piece if their combined thickness is more than the thickness of any other wood in the heat chamber. For example, if you make a pallet that has 3/4" deckboards attached to 5/4" stringers and these are stacked in the heat chamber, then the two 3/4" deckboards that sit "one on top of the other" equal 1-1/2" and this is considered the thickest piece of wood in the heat chamber. Probes cannot be sandwiched between these two pieces so in this situation surrogate blocks should be used with the probes to measure the temperature in the heat chamber. These surrogate blocks should be of like or similar species to the wood used in the pallets, as thick as the thickest wood in the heat chamber (as described earlier) and once probed, located in the same location as where the probe would be in a pallet. These blocks should also be in the same condition as the pallets before going into the chamber. For example, if your pallets have been sitting in colder weather conditions your surrogate blocks should be in the same condition when placed in the heat chamber with the pallets. According to ALSC, this will ensure that the pallets in the heat chamber reach the required temperature for conformance. Please let your inspector know if you have any questions regarding this.
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