Installation and putting into operation of a dynamic test gas stream

Status:

completed 12/2020

Aims:

The IFA has maintained a dynamic test gas stream since 2006. This facility is used firstly for validating the IFA's gas and vapour measurement methods, and secondly for interlaboratory (round robin) tests for test bodies. A dynamic test gas stream enables the climatic conditions occurring at workplaces to be simulated.

The move to a new laboratory building presented an opportunity for a larger and more powerful test gas stream to be set up. The existing test gas stream had reached the limits of its size and performance. In particular, enhanced selection of the climatic conditions and significant improvements to the control technology are intended to increase the new test gas stream's flexibility.

This is important with respect to the development of measurement methods and the performance of interlaboratory tests.

The aim of the project was to set up a more powerful dynamic test gas stream and put it into operation. Doubling the possible number of participants in simultaneous sampling was intended to yield a significant improvement to interlaboratory tests.

Activities/Methods:

Once it had been set up, the dynamic test gas stream was to be connected to the building's utilities. This concerned the gas and electrical supplies, commissioning of the thermostatic control system, and assurance of complete exhaust of the volatile substances exiting the dynamic test gas stream.

Checks were then to be performed to determine whether all required combinations of atmospheric humidity, temperature and air flow rate could be attained and controlled over the entire dynamic test gas stream. Following performance of the functional test, three online monitoring systems were to be coupled to the test gas stream, and the system's blank reading values checked. The selected ion flow tube mass spectrometer (SIFT-MS) analysis systems, an online gas chromatograph with thermal desorber, and a conventional flame ionization detector were to be connected to the test gas stream. The function of all items of equipment was to be tested comprehensively.

Following coupling of the online systems, the complementary gas was to be checked against the requirements. The complementary gas is produced in a two-stage purification process from the laboratory's own pre-purified compressed air; it must be free of volatile organic impurities.

Finally, test gases containing volatile substances for different concentration ranges had to be produced to enable both production and quality of the test gas and online monitoring to be tested. These tests were also to check the equivalence of the sampling points over the entire length of the test gas stream.

Results:

The test gas stream was first set up and connected to the relevant utilities, and the air exhaust system was installed.

The climatic settings were checked with variation of the flow rate, humidity and temperature. The condenser originally planned for the system was found to be not sufficiently powerful. The supplier was required to make improvements, and installed an additional two-stage condenser.

This condenser assured full climatic control over the entire system, and permitted adjustment of the different climatic conditions in the control software. The optimum settings in the control software were determined experimentally in extensive trials.

Once the climatic parameters had been determined, preliminary tests were carried out with test gas to determine the test gas stream's fitness for purpose. The laboratory's own compressed air is purified of traces of residual organic impurities by a multi-stage purification unit; blank reading values are negligible. The long-term stability of metering was verified by means of a solvent test gas (standard mixture of nine solvents) with the use of online gas chromatography. To determine the uniformity of the sampling points for test gases over the entire course of the stream, the composition of samples was checked at all sampling points by means of an online SIFT mass spectrometer; samples were also taken at each sampling point and analysed offline by the IFA's standard method for solvents. The uniformity meets the requirements for the scatter between sampling points to be below 2.0%.

Finally, the test gas stream's suitability for the measurement of volatile organic compounds (VOCs) was demonstrated in the interlaboratory test. The results of this interlaboratory test satisfied all requirements.

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