FLAMMSCHUTZMITTEL

Steel, wood and other structural elements and substrates are flameproofed by being coated with a composition comprising at least one metal salt of a phosphonocarboxylic or phosphonophosphonic acid of the formula in which R1=a carboxy group, a phosphono group, an alkyl, alkoxy or alkylamino radical optionally substituted one or more times by oxygen and/or nitrogen and containing at least one substituent from the group comprising the substitutents -COOH and -PO3H2, the alkyl group containing from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms, and the sum of the number of carboxyl and phosphono groups being from 1 to 8, preferably from 1 to 4; or a hydroxyalkyl or aminoalkyl radical containing from 1 to 12 and preferably from 1 to 4 carbon atoms, R2=hydrogen, chlorine, bromine, an alkyl radical with 1 to 12 carbon atoms, preferably with 1 to 4 carbon atoms; a hydroxyl, amino, acylamino such as C1-4-alkanoylamino, ureido, carbamoyl, phenyl, carboxyl or phosphono group, R3=hydrogen, chlorine, bromine, an alkyl radical with 1 to 12 carbon atoms, preferably with 1 to 4 carbon atoms, a phenyl radical or the groups mentioned for R1, but independently of R1, and R2 and R3 together may, with the carbon atom to which they are attached, form a 5- to 7-membered carbocyclic ring which may optionally be interrupted by nitrogen, or R2 and R3 together may represent an alkylene radical, preferably a methylene radical, or a C1-4, preferably C1-2, alkylene radical optionally substituted by phosphono groups and/or carboxyl groups; or together R2 and R3 may represent a double-bonded oxygen atom. Upon heating, the salt forms a foam which protects the substrate.