Comparison of portable, real-time dust monitors sampling actively, with size-selective adaptors, and passively

The performance of three, portable, real-time dust monitors was investigated inside a calm air dust chamber for a range of industrial dusts and two sizes of aluminium oxide dust. The instruments tested were the Split 2 (SKC Ltd), Microdust Pro (Casella Ltd) and DataRam (Thermo Electron Ltd), which sampled either passively or actively by connecting a manufacturer-supplied, size-selective adaptor and an air sampling pump to the inlet of the monitor. Two size-selective adaptors were tested with the Split 2: the GS-3 cyclone adaptor and the Institute of Occupational Medicine (IOM) inlet with porous foam inserts. Similarly, two size-selective adaptors were tested with the Microdust Pro: the Higgins-Dewell cyclone adaptor and the conical inhalable sampler (CIS) adaptor with porous foam inserts. The DataRam was tested with a GK 2.05 cyclone adaptor since there was no porous foam adaptor available. The instruments' responses were compared with the reference dust samplers: Casella Higgins-Dewell cyclone for the respirable fraction and IOM sampler for the inhalable fraction. The response of the dust monitors was found to be linear with respirable dust concentration when operated either passively or actively using the cyclone size-selective inlets. Their responses were, however, lower when operated actively with the cyclone adaptors compared to the passive operation and lower still when used with the porous foam inserts. There was also often more scatter in the porous foam measurements, attributable to variable clogging of the foams caused by inconsistent loading with dust. The dust monitor responses were sensitive to changes in particle size when operated passively but much less so in active mode with the cyclone adaptors. The Microdust Higgins-Dewell cyclone adaptor measurements agreed closely with the reference respirable concentration for all dusts, whereas those for the DataRam GK 2.05 and Split 2 GS-3 cyclone adaptors were different to the reference. Concentrations measured with the foam adaptors were considerably lower than both the reference cyclone samplers and the dust monitor cyclone adaptors and increasingly undersampled as they became loaded with dust. Inhalable dust measured with the Split 2 IOM adaptor agreed closely with the reference IOM inhalable samplers, whereas the Microdust CIS adaptor underestimated the inhalable concentration compared to the reference.