On-Site Inspection of the Humidity-Controlled Warm-Air Treatment Facilities for the Bell Tower of Okariden Hall
On May 15, 2024, we visited Nikko Toshogu Shrine to inspect the “humidity-controlled warm-air treatment” facilities for the bell tower of Okariden Hall. Traditional gas fumigation for insect extermination has become difficult to continue due to safety and environmental concerns. This new treatment is a method to exterminate insects that damage the wood of structures, such as pillars and beams, by heating the wood to high temperatures (around 60℃). By controlling the humidity during the treatment to maintain a constant moisture content in the wood, it is possible to raise the temperature inside the wood without significantly affecting its physical properties. The new method is therefore expected to be a means to replace gas fumigation.
To date, the research team, consisting of the Association for the Preservation of the Nikko World Heritage Site Shrines and Temples, Kyoto University, Total System Laboratory, Kansai Electric Power Co., Inc., KANSO Technos Co., Ltd., and the Tokyo National Research Institute for Cultural Properties (TOBUNKEN), has conducted three verification treatments on actual buildings. In addition to evaluating the insecticidal effects and impact on the structures, considerations were also given to environmental impacts such as noise and energy consumption. As a result, the humidity-controlled warm-air treatment was established as a practicable new method for insect extermination in wooden structures.
Last year, for the first time on a designated cultural property, the treatment was carried out at the Gohotendo Hall of Rinnoji Temple. This time, it was conducted at the bell tower of Okariden Hall, marking the second case for a designated cultural property. Going forward, we aim to promote this method as the new standard for insect extermination in wooden structures.