Abstract: A flame ionization detector adapted for use in hazardous areas and for mounting in any attitude, capable of using as small a flame as can be dependably maintained because of an arrangement of the flame at the open end of a thin-walled small diameter tubular electrode inside a relatively long open ended cylindrical collector and the regulation of the rates of flows which make it possible to maximize the sensitivity of the detector to the presence of an organic vapor. Excess air is maintained at a predetermined minimum. The inside diameter of the collector is made approximately twice the visible diameter of the widest point of the flame. A curtain of air flowing at a predetermined rate through the annular passage between the electrode and collector is directed into encompassing contact with the flame and the proximity of the collector to the flame maintains a relatively dense ion bearing layer of gases at the surface of the collector.