Work has been carried out in two laboratories to consider the requirement of extending the definition of inhalability into low air movement environments, typical of many modern workplaces and indoor environments. The work has focused on two aspects, the development of a method fur measurement of the aspiration efficiency of a breathing manikin (which is the basis of the current convention) in these conditions, and the subsequent measurement of that efficiency. A method has been devised for testing manikin aspiration efficiency in low: air movement environments conditions using a chamber of dimensions approximately 1 m x 1 m x 3 m with pseudo-isokinetic reference probes circling about a vertical axis. This method has been shown to give consistent results between the laboratories, with significantly lower uncertainty than applies in wind tunnels. The manikin aspiration efficiency, tested at three breathing rates and over a range of particle aerodynamic diameters, was found to rise with breathing rate and be consistently higher than the existing convention. The results obtained indicate that human inhalability in low air movement environments may be significantly greater than that in moving air conditions with a maximum bias of 48% being measured. A revised form of the: inhalable convention for low air movement environments is suggested.