Vacuum-steam Phytosanitation of hardwood pallets and pallet stringers

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Date: May 2012
From: Forest Products Journal(Vol. 62, Issue 5)
Publisher: Forest Products Society
Document Type: Abstract
Length: 3,074 words
Lexile Measure: 1300L

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Abstract

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[degrees]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 holding time of 30 minutes. The average treatment times of dry pallets were 7.1 and 10.4 percent faster than green pallets at 400 and 665 mbar, respectively. Wood species affected the treatment time. The average treatment time of dry yellow-poplar pallets was 15.9 percent faster than that of dry red oak pallets at 400 mbar. Pressure also affected the treatment duration. The stringers could be successfully treated even when they were arranged in various stacking patterns. The moisture content increased after the treatment, but the change was less than 3 percent for both green and dry pallets.

Wood packaging material has been a vector for the intercontinental movement of pests that threaten forest resources. Over 400 insects that feed on trees and shrubs have been introduced into the United States in the last 200 years primarily through the use of cargo containers in world trade (Haack 2006). Reducing the spread of forest pests is a national and international priority, and the United States along with 133 other countries has been implementing the International Standards for Phytosanitary Measures (ISPM) No. 15 to stop or significantly reduce the spread of wood pests around the globe via solid wood packaging material. ISPM 15 requires solid wood packaging materials including wood pallets and containers used for exporting products to be treated (Food and Agriculture Organization of the United Nations 2002, revised 2009). Approved treatment methods include methyl bromide gas fumigant application and heat treatment in which wood is continuously heated for 30 minutes to achieve a minimum temperature of 56[degrees]C throughout the profile of the wood. Vacuum-steam treatment of pallets and other raw wood packaging material is more efficient than the current hot air heat treatment (Chen and White 2012). The mechanism of sanitation is the same as convective hot air heat treatment and thus complies with ISPM 15. Previous research indicates that the higher efficiency of vacuum-steam treatment compared with convection systems is associated with the higher heat capacity of saturated steam Using saturated steam under vacuum, treatment temperatures are well below...

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Gale Document Number: GALE|A318492651