An analysis of rural fires in Iowa shows that sparks ejected from house chimneys and falling on combustible roofs account for a large portion of the total fire waste. These sparks originate from soot deposits on the chimney wall, which upon being ignited are loosened and carried out by the chimney gases. If the combustion in the firebox were reasonably complete or if the chimney were kept clean by mechanical means, the soot accumulations would not occur. If the roof were of fireproof or fire-resisting material, the sparks would not constitute a serious problem as is now the case.

The use of a spark arrester, as considered in this manuscript, is an attempt to remedy a bad situation.

Spark arresters have been used successfully on locomotives and industrial chimneys for years. Their application to residences is comparatively recent and a different problem from their industrial use; spark arresters used with success industrially will not operate satisfactorily on dwellings. Therefore this study was made to discover the requirements of a domestic spark arrester. the suitability of a number being offered for sale and the possible design of one which might perform 'a better service.

In density and in burning characteristics sparks of incandescent soot escaping from the chimney differ considerably from ,wood embers flying from a burning building. The first section of this study was devoted to a determination of the source and character of these sparks and the condition under which they might ignite both new and weathered wood shingles. Investigations were made of flue gas velocities as may occur in domestic chimneys and those velocities necessary to expel soot particles of dangerous size.