Gastec Benzene Gas Detector Tube features 3 pump strokes and 1 correction factor for 0.2 - 20 ppm measuring range and 1 pump strokes and 3.3 correction factor for 20 - 66 ppm measuring range. Detector tube with sampling time of 2 min per pump stroke is ideal to detect benzene in air or the industrial areas and environmental atmospheric condition. Detector with 0.1 ppm detecting limit, changes color from white to brown.