The Influence of Different Types of Expandable Graphite on the Thermal Resistance of Spruce Wood

In order to not limit the possibilities of using wood due to its flammability, the implementation of fire protection is an essential requirement. An integral part of the research on the fire protection of wood is the determination of the effectiveness of the applied protective means and their effect on changing its behavior under fire conditions. In this work, samples of spruce wood (Picea abies (L.) H. Karst) (50 mm × 40 mm × 10 mm) were treated with an aqueous solution of sodium silicate and different types of expandable graphite flakes that were applied to the surface of the samples. The fire characteristics of the samples were studied using a non-standard test method, the radiant heat source test, which was used to determine the mass loss, burning rate, and ignition time of the test samples, and the measurement was carried out via visual recording with a thermal camera. The results of the laboratory test method showed a significant positive effect of the application of all types of expandable graphite flakes. The main insight is that a suitable wood modification using expandable graphite flakes in combination with water glass has the potential to reduce mass loss by at least 73 ± 3% and reduce the temperature rise on the surface of the sample. The lower temperature of the surface of the burning material reduces the possibility of heat transfer to the surrounding materials and thus reduces the rate of fire spread.