The color change analysis of historic wooden remains after fire-suppression by fluorinated chemical gases

Abstract

Many wooden Chinese historic buildings are destroyed due to the ravages of frequent fire disasters. The fire risk of historic buildings are highly enlarged since a long-time weathered wooden structures in the natural environment. The clean fire-extinguishing technology using fluorinated chemical gases to put out a historic building fire rapidly at the initial stage is highly recommended and widely used. However, the gaseous hydrogen fluoride (HF) yielded during the fire suppression process could be a potential method to result in secondary damage due to its corrosiveness. Nowadays, experiments were employed to clarify the effect of fire suppression on the surface of historic wooden buildings. Five traditional fluorinated chemical gases, H-37, FK-5-1-12, H-1323, H-2402, and H-1301, are used to suppress a fixed flame. The wooden samples, including a Dao Talisman board, a painting paper, and wooden chips, are placed in a chamber. Wooden chips consist of traditional and weathered samples (acting as the Chinese historic buildings). The concentration of gaseous products yielded from fire suppression are monitored by a gas-FTIR from ABB, and the surface analysis is conducted by a Quanta FEG SEM–EDX from FEI. It is observed that flame enhancement happens at the early stage of fire suppression and varies with fire agents. The amount of F-deposited on the wooden surface is positively correlated with a total amount of gaseous HF. The color change mechanism of the wooden surface is comprehensive, although the amount of HF is a leading factor. The influence of HF on color change depends on the amount of both gaseous H2O and HF. It is concluded that the value of L* of the traditional chip is much easier to be reduced comparing with weathered samples with the same wood grain. The reduction of {mathrm{b}}^{*} value of weathered samples is much larger than the traditional ones. It suggests the weathered chips show a color shift toward blue because of fire suppression. The present study hopes to provide a basic acknowledgment for the comprehensive understanding of secondary damage caused by fire suppression.