Why doesn't the plume sometimes ignite? I know methane is lighter than air so it would rise straight up, subject to winds. Seems like an electrostatic spark f

Why doesn't the plume sometimes ignite? I know methane is lighter than air so it would rise straight up, subject to winds. Seems like an electrostatic spark from say dust in the air would happen once in a while and ignite the plume. Or some kid launching a bottle rocket on a day with sideways winds. Maybe the gas concentration quickly becomes too low to ignite?