(NH4)(2)SO4 and (NH4)H2PO4 are the principal components in the powder material used in fire extinguishers. In this paper the mutual influence in their thermal decomposition is investigated by thermogravimetry. Two methods for the quantification of both salts in mixtures (NH4)(2)SO4/(NH4)H2PO4 are proposed. The first employs thermogravinnetry and is based on the measurement of the mass fraction in the 500-550 degrees C interval, once (NH4)2SO4 has totally decomposed to yield gaseous products. The second uses some selected peaks in the X-ray diffractogram. (c) 2006 Elsevier B.V. All rights reserved.