A method and apparatus are disclosed for operating a combustion device during a transient operation. The combustion device is fed with at least a fuel. The transient operation includes a period having a period length (T) during which the fuel is fed in an amount lower that a designated (e.g., critical) amount (Mc). A limit value (L) is defined for the period length (T), and fuel feed is regulated to keep the period length (T) smaller or equal to the limit value (L).