Where, LFL is the lower flammable limit in kg/m3 for the refrigerant used. If the charge amount in the system is below m1 then minimum requirements for the refrigerants have to be met. When the charge level is greater than m1 and less than m2, then in along with the minimum requirements,additional restrictions apply to the allowable room size. If the charge amount is greater than m2 and less than m3 then national standards apply.