It was found that stone dust, being inert and inflammable, when scattered incorrect amounts around the mine, would break the chain of flammable coal dust particles, thus helping to check the onset of the flame front. But explosions were still taking place in the early years of the twentieth century and were documented, for example, in the book by Mr. T. H. Byrom, F.I.C., 'The Physics and Chemistry of Mining', dated 1905. In which is said: 'The application of stone-dust is undoubtedly beneficial in preventing the explosion of coal dust'.  Stone dust was not the only material used; Shale, Fullers Earth, Gypsum, etc. were all used for this purpose. The mixture used varied widely, with some authority's advocating a 50 / 50 mix of stone dust and coal dust; while other, equally eminent, men disagreed with these findings, and suggested a mix of 25 / 75 mix, with the final mixture being dependant on the volatility of the coal being mined. Quoting from E. Mason's excellent books 'Practical Coal Mining' 1953 3rd. edition: In 1923, the S.M.R.B. conducted experiments at Eskmeals which proved conclusively that the 1 / 1 mixtures of coal and stone dust did not ensure safety. This result had been arrived at previously in the U.S.A. Bureau of Mines experiments. In view of these results, and because of the failure of these regulations in force to prevent coal dust explosions. Further regulations were enacted in 1939. These were temporarily amended so that the maximum percentage of incombustible matter required was 65 percent. The actual amount of inert matter required is dependant on the volatile content of the coal.