An assembly of two gas filters on the front side of the detector filters the supplied gas internally before it is used in the detector. The gas filters consist of a charcoal filter and a high-efficiency particulate air (HEPA) filter. Gas supplied through the gas inlet of the detector is first filtered in the charcoal gas filter (bottom filter) and then in the HEPA gas filter (top filter).
Sufficient filtering of the supplied gas, both externally and internally, ensures that the gas is clean and free from particles.