Activated carbon is the most commonly used adsorbent for filtering harmful gaseous chemicals from air and is a standard component of CBRN air filters. If a pollutant is present in air that is passed through activated carbon, it adsorbs the substance in question until its surface is saturated. Hereafter, the filtration efficiency drops drastically and a filter break-through occurs. In contrast to mechanically filtering materials (fiber filters), the increasing saturation of activated carbon filters cannot be detected by a change in its resistance to airflow (pressure drop). Despite intensive research in the field of gas sensors, sensor systems for monitoring the residual activity of activated carbon filters for ABC protection are currently not available to professional users in Austria. Major challenges in the development of a corresponding sensor technology are robustness, sensitivity, susceptibility to failure, power consumption, manufacturing costs per filter unit and suitability for retrofitting. In any case, a single point measurement in the filter is not sufficient. The activated carbon saturation must be monitored at least at several points along the filter and across the filter cross-section.
Within project SAFE, two sensor technologies for this kind of monitoring shall be tested: 1) electronic impedance tomography (EIT) and 2) field-effect transistor (FET) sensors. Both technologies, EIT and FET sensors, detect changes in surface conductivity with high sensitivity, which occur e.g. upon adsorption of chemicals onto activated carbon. Eventually, EIT and FET sensors shall be used in combination in a filter cartridge to track the progressive filter saturation. It shall be tested whether higher reliability or fail-safety can be achieved by this approach or whether a more efficient monitoring solution can be implemented than by using one of the two technologies alone. The complex measurement data shall be interpreted automatically using AI-supported evaluation software, which is also supposed to be developed within the activity.
The project focuses on the mobile use of the developed sensor system in a CBRN protection vehicle, but the stationary use in air filter systems in military and civilian buildings and facilities is also taken into account. The aim of the project is to validate the sensor concept in a laboratory environment (TRL4). For this purpose, the exposure of activated carbon filter materials to established chemical warfare agent simulants as well as relevant environmental influences (especially atmospheric humidity, ambient temperature, exhaust gases) in a test setup shall be tested and the response of the sensor system to these influences shall be investigated.
