Here is some background for those unfamiliar with methane. I got this from Wikipedia:
Methane is not toxic; however, it is extremely flammable and may form explosive mixtures with air. Methane is violently reactive with oxidizers, halogens, and some halogen-containing compounds. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia may result if the oxygen concentration is reduced to below about 16% by displacement, as most people can tolerate a reduction from 21% to 16% without ill effects. The concentration of methane at which asphyxiation risk becomes significant is much higher than the 5–15% concentration in a flammable or explosive mixture. Possible health effects of breathing in methane at high concentrations, resulting in oxygen deficiency, are increased breathing and pulse rates, lack of muscular coordination, emotional upset, nausea and vomiting, loss of consciousness, respiratory collapse and death. Methane off-gas can penetrate the interiors of buildings near landfills and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture this gas and vent it away from the building.
Methane gas explosions are responsible for many deadly mining disasters. A methane gas explosion was the cause of the Upper Big Branch coal mine disaster in West Virginia on April 5, 2010, killing 25.
There are some variables here that one would have to accurately measure to know if an explosion hazard exists. Here is what the CDC says about the explosion hazards of methane in landfills and the conditions that have to be met for an explosion to occur.
http://www.atsdr.cdc.gov/hac/landfill/html/ch3.htmlI know that methane is a
huge deal at the coal mines I have been to. But, I am not knowledgeable with methane to air ratio in typical landfill gas gathering lines. Nor do I know how much it can fluctuate or concentrate given various conditions. Based on the Wiki article it would seem that it is quite possible to have dangerous concentrations and methane to air mixture. So personally, I would most definitely err on the side of caution. This is even more true if I were in a ditch. McElroy has a procedure for fusing in gaseous or explosive environments. It is documented in the manual for any given machine. I would use these fusion procedures if I weren't able to shut the flow off and vent the area.
I would encourage you to research this question within your industry and with those who would be more familiar with the potential hazards you're working with. I would bet that there are generally accepted industry guidelines out there somewhere.
I moved this post to the Technical Support area of this forum. Please feel free to post there with any more solid information that you find. I am interested to know.