Contribution of metastable levels to the radiative loss rates shown relatively to the radiative loss rates only from the ground level for Be-like oxygen. The red solid line, green dash-dotted line, and blue dotted line represent the ratio of the total radiative loss rate from the second level (lev = 2), the third level (lev = 3), and the fourth level (lev = 4) relatively tothe radiative loss from the ground level (lev = 1), respectively. The definition of metastable levels can be found in Table 6.