The influence of ammomnium salts of oligomeric Br-N-containing sulphonic acids and some inorganic fire retardants on the physico-mechanical properties, flammability characteristics, and thermooxidative degradation of EPM compositions for insulation of ship cables has been studied. The ternary system consisting of bromosulphaminic acid bromonitrosulphonic acid and antimony trioxide in 6.6 : 3.4 : 4–5 mass ratio has been found to exhibit an addictive effect on the fire retardancy. A correlation between the flammability characteristics and some thermal properties of EPM compositions has also been established. The organic fire retardants of certain concentrations in EPM compositions have been found to exhibit a positive plasticizing performance. © 1993 John Wiley & Sons, Inc.