Recently at our gas plant fugitive emissions monitoring activity is being carried out. Prior to this vulnerable points marked like flanges, blinds, bleeders, valve packing & so on. we have observed that at some points gas testers detect 30,000 ppm (3%) to 50,000 ppm (5%) so far at the tip of sources. Our plant gas specs is 80% methane 19% N2 & 1% CO2. There are around 50 pair pole mounted line of sight gas detectors (at 15' to 17' max) are installed covering whole process area. Detectors are calibrated on methane 2.5% LEL & 5% HEL. My question here is why LOS are unable to detect the methane gas? other concern is that while methane is being leaked 3% to 5% & if it gets heat source is there any chance of fire?