The design of topsides against explosions requires the definition of a design over-pressure, however, these values are often treated as deterministic and there is a wide variation within the industry in the treatment and interpretation of the loads. This paper advocates the adoption of a number of limit state for explosion loading. Events of different magnitudes are differentiated on the basis of frequency and linked to appropriate degree of reliability thus avoiding disproportionate effects from minor events. The two principal limit states considered are a limit state for all the safety critical systems for relatively high frequency events and a survival condition for low probability events. Parallels are drawn from other branches of engineering where extreme loads have to be designed for.