described in astm special technical publication 422 1969 and nfpa 258 t 34 smoke generated by solid materials 34 may 1974 using the flaming mode of operation all results are the average of two or more values and are reported as the maximum corrected specific optical density d mc percent smoke reduction is calculated using the equation the following examples illustrate the present invention but are not intended to limit the invention thereto the following examples show the effect of several smoke suppressants in general purpose polystyrene a homopolymer containing 15 phr parts per hundred parts resin of 1 2 bis 2 4 6 tribromophenoxy ethane the data indicated in table 1 show that sodium tetraborate pentahydrate is a much more effective smoke suppressant than the other commercially available sodium tetraborates it is also more effective than sodium metaborate sodium perborate zinc borate and potassium borate table i__________________________________________________________________________ smoke suppressantexample no smoke suppressant content phr sup d mc reduction__________________________________________________________________________1 control 730 2 na sub 2 b sub 4 o sub 7 5h sub 2 o 15 482 343 na sub 2 b sub 4 o sub 7 10h sub 2 o borax 15 705 34 na sub 2 b sub 4 o sub 7 anhydrous 15 592 195 k sub.