ILK Dresden - Institute of Air Handling Hall 8 / A30

As part of the health protection of employees, occupational exposure limits are set for hazardous substances, which must be complied with by the operators of plants and companies. These regulations can be achieved by a near-source capture of the emissions and a separation of the hazardous substances by industrial vacuum cleaners and dust extractors that are equipped with filter elements made of highly efficient filter materials. These materials must be tested regarding their penetration rate in accordance with IEC 60335-2-69 annex AA. The test method described within this standard uses a photometer or a suitable measuring system to determine the concentrations used to evaluate the separation efficiency. The traceability of a photometer within the scope of accreditation is difficult to implement. For this reason, a test stand using a gravimetric measuring method was established at the Institut für Luft- und Kältetechnik in Dresden. Investigations into the limit of quantification have shown, that this measuring method is sensitive enough to reliably determine the dust classes “L” and “M”. Difficulties, limitations and new developments concerning the essential filter material test will be discussed.

Sorption material in gas cleaning units that serve occupational health and safety must be changed at an appropriate early stage. The instructions from the professional associations stipulate that driver's cabs must have an appropriately equipped ventilation system when used in contaminated areas. However, the standards for the sorption filter specified in the document only contain the type of filter test and no recommendations for the duration of use. The research project at the ILK Dresden aims to develop a sensor system for the safe monitoring of the operating status of a sorption device for the separation of gaseous substances from air. The sensor we develop will convert the loading status of the sorption agent into an electrical signal so that a warning message can be issued to the user or the system control when a threshold value is reached. The measurement is carried out via the electrical capacitance at a frequency and a specific measuring voltage. Capacitance/voltage converters are used, which enable a simple evaluation to be carried out. Such ICs (interdigital circuits) cost between 10 and 30 €. The evaluation unit includes the sensor unit, so they are reusable. The price also allows several sensor elements to be queried in the filter element, which means that the resolution of the adsorption front can be mapped more precisely. It is essential to record the moisture, as the water retention dominates the loading of the sorbent. This observation is confirmed by measurements carried out at the ILK Dresden on pollutant filters actually used. The filter elements used were exposed to 70% humidity and the test gas cyclohexane at the nominal volume flow. One filter element showed an immediate breakthrough with the simultaneous release of moisture into the clean gas. The sorbent is evidently saturated with water. Therefore, sensor elements for temperature and humidity are placed up and downstream of the filter. We prefer printed electronics for these sensors. Results will be discussed...