How do we compare peak side-on overpressure loads with different duration? For example a 100kPa for a 70milsec duration and a 170kPa for a 20milsec duration.
John, it is unclear what you are trying to solve, but the different durations mean that the impulse will be different (impulse = force X duration). Structural configurations can be analyzed dynamically when pressure and impulse are known.
If you are designing a blast-resistant component, you need a specialist.
The positive phase of the pressue is said to go to zero at the time of duration and therefore the impulse is the triangle under the curve. The impulse in your first case is twice that of your second case. That's why components need to be designed for more than just pressure. You may also need to look at the reflected pressures and not just the side-on values. The reflected pressure may be twice or more compared to your side-on values.
How your system reacts to the pressures and durations is where the dilliculty resides.