The X-pid has been developed for applications where VOCs are frequently and, above all else, selectively measured in low concentrations. Selective means that the device not only detects the overall concentration, but also the individual substances. The abbreviation “pid” stands for photoionization detector. This exposes the collected ambient air to the UV light of a gas discharge lamp in a measuring chamber. This intensive light can ionize gas molecules so that electrons are released from the molecules, creating a measurement current, which is analyzed by the detector as a measurement signal.
In the first measurement stage (“Seeker” mode), the total concentration is read and displayed. In the second stage (“Analysis” mode), gas chromatography measures selected target compounds. The analysis breaks down the broad overview provided by the seeker into single concentrations (substance by substance). Deichmann has incorporated both the measurement device and the process in a company directive for quality control. “Before any container is opened, a measurement must be taken to provide a guide value of the level of harmful substances inside,” states the directive. “The Dräger X-pid 9500 gas measurement device must be used for this purpose.”
From the data gathered in the testing laboratories, Deichmann knew that it was dealing with 16 relevant substances that can be harmful to human health. Most prominent among these are benzene and toluene. When it came to setting the threshold limits, the company played it safe. By its own account, compared to other players in the industry, the limits were set low. In simplified terms, depending on the threshold value, the following has applied ever since: A container can be unloaded if the total concentration is less than ten parts per million (ppm). Experience shows that there is no need to take action here. With concentrations of up to 50 ppm, a second measurement is mandatory. In such cases, it is to be expected that the concentration of individual VOCs exceeds the critical level. The container may not be opened if the figure is higher than 50 ppm. Instead, it must be ventilated together with its load until the concentration has dropped to a safe level. If this doesn’t work, the consignment is sent back. “Critical thresholds are exceeded here once or twice a month,” says quality assurance manager Marcel Cornelissen. “The problem can usually be solved with fresh air.”