(W1030-08-46) Determination of the Evacuation Time of a Newly Developed Chamber Setup for the Investigation of the Spatial Dust Distribution of Pharmaceutical Powders

Purpose: Lately, various chambers for dustiness measurements of powders have been described. However so far only the dustiness itself and not the spatial distribution of the dust has been investigated. Therefore, a novel chamber setup with defined measuring points has been developed to obtain stationary exposure data on the dust formation of pharmaceutical powders. The objective of this study was to determine the evacuation time required to gather the entire content of the detection chamber with the fume of sulfuric acid as a model aerosol.

Methods: The experimental setup consists of two connected chambers, the emission chamber and the detection chamber, as shown in Figure 1. The inner dimensions of the emission chamber are 194 mm × 194 mm × 194 mm resulting in a volume of approximately 7.3 l. The detection chamber shows inner dimensions of 1000 mm × 1000 mm × 1000 mm which results in a volume of 1000 l. An airflow test tube containing fuming sulfuric acid was inserted into the pressurized air pipe between the source of compressed air and the double-acting ball valve. Subsequently, the 3/2-way valve and the double-acting ball valve, controlled by a programmable logic controller (PLC) and positioned above the emission chamber (Figure 2), were opened. By this means, the fume of sulfuric acid was introduced into the emission chamber for 60 s. Simultaneously, the 3/2-way valve between the sampling pump and the 9 IOM samplers (Institute of Occupational Medicine) in the detection chamber was activated, generating an airflow of 2 l/min through each of the samplers. Through the connecting orifice with a diameter of 25.4 mm, the fume flowed from the emission into the detection chamber and was evacuated through the 9 IOM samplers. During the experimental procedure pictures of the cross-sectional area of the detection chamber were taken every 10 s. This series of pictures was subsequently examined via image analysis using the software ImageJ (NIH). For this analysis, the optical fume density in the pictures based on the mean grey value in each of four different zones selected around the center (390 × 390 pixels) was evaluated via nonlinear regression.

Results: The results of the evacuation time investigation are shown in Figure 3. The maximum mean grey value of the fume density corrected by the asymptote values of the individual evacuation runs over the time course of the experiments was decided to be 100 % and the corresponding time point was set to 0 s. The decrease of the fume density over time followed an exponential decrease and the asymptote of the nonlinear regression was set to 0 %. As this value will only be reached at infinite time, the chamber was regarded to be completely evacuated as soon as the residual fume density fell below a value of 1 %. Based on these findings, the evacuation of the detection chamber took 16700 s. At a flow rate of 2 l/min for each of the 9 IOM samplers and a detection chamber volume of 1000 l, the evacuation time corresponds to an approximately fivefold air exchange.

Conclusion: The present study demonstrated that the newly developed chamber setup is capable of producing a controlled and directed airflow through the emission chamber into the detection chamber. In addition, the detection chamber may be successfully evacuated through the IOM samplers by the generated vacuum of the sampling pump. According to the results of the fume experiments a fivefold air exchange was required for complete evacuation of the detection chamber. Future investigations with pharmaceutical powders will show whether a decrease of the necessary evacuation time and thus a reduction of the number of air exchanges is possible to obtain reproducible spatial dust distributions.


Figure 1: Simplified illustration of the novel chamber setup for the investigation of the spatial dust distribution.


Figure 2: Simplified piping and instrumentation diagram of the chamber setup.


Figure 3: Time course of the relative fume density (means ± SD, n = 3).