Quantitative measurements of the total heat release by selected building materials were made during an interlaboratory study of the Potential Heat Method. Seven of the eleven participating laboratories ranked the five materials in the same order, and a single ranking change for three other laboratories would yield identical rankings. The general magnitude of within-laboratory repeatability and between-laboratory reproducibility for composite materials of generally low potential heat are indicated by statistical analysis of the results.

Results are reported on the effect of the amount of combustion promoter used and on differences in the first and second phase values. A discussion is presented on the effects of material sampling and on certain features of the experimental procedure which require special care. A tentative test method standard, containing complete details of the test procedure, is included as an appendix.