AP4C detects the atoms of phosphorus (contained in all G, V agents: GA, GB, GD, GE, GF, VE, VX), the atoms of sulfur (contained in H, HD, HL agents), the HNO spectrum (used to detect HN, HCN), the As spectrum (contained in L, SA, DM). The AP4C use a 5^th channel to detect the CH spectrum and to indicate, at 10% of the level, the flammability of the air. The high sensitivity and fast response time make the AP4C especially suitable to check up contamination.