<prompt> To what extent must the oxygen content be reduced before an explosion of methane and air is impossible?12 percent10 percent11 percent7 percent  <response>: For a mixture of strictly methane and air, the oxygen content must be 12 percent or less. It is however, significant to note that there is a combination of combustible gases following explosions and during fires.So the maximum allowable oxygen will vary according to variations in the combustible and inert gases. 