Direct-reading inhalable dust monitoring--an assessment of current measurement methods.

Direct-reading dust monitors designed specifically to measure the inhalable fraction of airborne dust are not widely available. Current practice therefore often involves comparing the response of photometer-type dust monitors with the concentration measured with a reference gravimetric inhalable sampler, which is used to adjust the dust monitor measurement. However, changes in airborne particle size can result in significant errors in the estimation of inhalable concentration by this method. The main aim of this study was to assess how these dust monitors behave when challenged with airborne dust containing particles in the inhalable size range and also to investigate alternative dust monitors whose response might not be as prone to variations in particle size or that could be adapted to measure inhalable dust concentration. Several photometer-type dust monitors and a Respicon TM, tapered element oscillating microbalance (TEOM) personal dust monitor (PDM) 3600, TEOM 1400, and Dustrak DRX were assessed for the measurement of airborne inhalable dust during laboratory and field trials. The PDM was modified to allow it to sample and measure larger particles in the inhalable size range. During the laboratory tests, the dust monitors and reference gravimetric samplers were challenged inside a large dust tunnel with aerosols of industrial dusts known to present an inhalable hazard and aluminium oxide powders with a range of discrete particle sizes. A constant concentration of each dust type was generated and peak concentrations of larger particles were periodically introduced to investigate the effects of sudden changes in particle size on monitor calibration. The PDM, Respicon, and DataRam photometer were also assessed during field trials at a bakery, joinery, and a grain mill. Laboratory results showed that the Respicon, modified PDM, and TEOM 1400 observed good linearity for all types of dust when compared with measurements made with a reference IOM sampler; the photometer-type dust monitors on the other hand showed little correlation. The Respicon also accurately measured the inhalable concentration, whereas the modified PDM underestimated it by ~27%. Photometer responses varied considerably with changing particle size, which resulted in appreciable errors in airborne inhalable dust concentration measurements. Similar trends were also observed during field trials. Despite having limitations, both the modified PDM and Respicon showed promise as real-time inhalable dust monitors.

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.

Evaluation of diffusive samplers and photoionisation detectors for measuring very short peak exposures in the workplace.

The extent to which very short peak widths, peak frequency, sampling time and post-sampling/pre-capping time impact upon occupational exposure measurements of toluene has been investigated using diffusive tubes. Additionally, the effect of the width of the peak on the estimation of peak maximum concentration and time-weighted average (TWA) concentration from real-time instruments (photoionisation detectors-PIDs) was also studied, and their responses modelled. No clear differences were perceived between diffusive and pumped tube results. Mean biases of -5 to +6% were recorded but no trend could be distinguished with respect to any of the variables examined; the main source of uncertainty was attributed to analytical uncertainty. The diffusive tubes can therefore be used to measure short term transient toluene concentrations (e.g. 5 s duration) over short (15 min) exposure periods. The two slower responding PIDs (t50 = 4 s) underestimated the maximum concentration of short term peaks having durations less than 10 s. The other three PIDs (t50 < or = 2 s) only significantly underestimated the maximum concentration of short term peaks having durations of 2 s and below. Pulse duration appeared to affect the PID's estimation of peak height more than peak area (TWA concentration).