The paper deals with monitoring retardant changes of lignocellulosic materials. Combustion of lignocellulosic materials and fire-technical characteristics are described. In assessing the retarding effect of salt NH4H2PO4, fire-technical characteristics as limiting oxygen index (LOI) were measured, and by using thermoanalytical TG and DSC methods. High-temperature process of cellulose degradation at various flame concentrations was studied.