Vacuum–Steam Phytosanitation of Hardwood Pallets and Pallet Stringers

The vacuum–steam treatment of pallets and pallet parts for compliance with the International Standards for Phytosanitary Measures No. 15 regulation was evaluated. Vacuum–steam treatment consists of four steps: (1) vacuum, (2) heating, (3) holding at an increased temperature for a period of time, and (4) cooling. The system produces steam and maintains the saturation or superheated state in a flexible container. Hardwood dry and green pallets (122 by 101.6 cm) and notched stringers (122 cm long) were treated. After the vacuum was drawn, steam was injected into the container to heat the pallets through condensation. The steam was turned off when the center of the pallets or stringers reached 56°C. The stringer parts were treated in three stacking patterns: deadpacked piles of 12, 2, and 5 layers in a stack. Vacuum–steam treatment is significantly faster than conventional convective hot air treatment. The pallets were treated in less than 65 minutes, which included a vacuum time of 5 minutes and a h...