The accumulation for a relief device is:

The correct answer is C because accumulation is defined (per CCPS and industry standards such as ASME) as the pressure increase above the relief device set pressure, expressed as a percentage of the set pressure .

When a relief device (such as a safety valve or rupture disc) activates, the system pressure is allowed to rise above the set pressure during discharge. This temporary pressure increase is called accumulation . It reflects the system’s ability to safely handle overpressure while the relief device is relieving excess energy or material.

Mathematically, accumulation is calculated as:

Option A is incorrect because accumulation is not referenced to MAWP. Option B describes pressure relative to MAWP, which is not the definition of accumulation. Option D is also incorrect because it mixes MAWP and set pressure improperly.

CCPS emphasizes understanding accumulation as part of pressure relief system design , ensuring that vessels can tolerate the maximum allowable accumulation (often 10% for single relief devices under many codes) without exceeding safe limits.