US Systems: A caveat! Remains of scavenged fuel-tank digesters after barn burned down around them in Missouri. (1983) (The fire was said to have been unrelated to the digesters – it would have exploded instead of just burned.) Methane at 4 to 14 % in air is very dangerous for explosions. Just don’t let it happen. You’al will certainly smell it — And it can be monitored.