Why measure methane?
The problem with methane isn’t so much that it’s toxic, but that, like butane, it’s explosive at high concentrations. The high alarm level set by the community is about one-tenth of what would be necessary to start a fire (5000 parts per million [ppm]), and the low alarm level (1000 ppm) is set to raise an early warning that levels are rising. The low alarm level has no health significance. In most cities in the United States, methane is detected frequently. Typically levels are below 1 ppm, except near landfills and some wetlands. Along the perimeter of the ConocoPhillips-Rodeo refinery, levels at the north fenceline are usually slightly higher than at the south fenceline, but levels are usually below 2 ppm.
