The required discharge area (A) calculation is iterative. You will need:
As of this writing (2025-2026), the most current version is . This revision incorporated significant updates to non-equilibrium modeling and clarified the application range of the homogeneous equilibrium method. Iso 4126-9 Pdf
Most traditional safety standards assume a homogenous fluid—either all gas or all liquid. However, real-world industrial upsets frequently involve (e.g., a mixture of liquid and vapor, or gas and solid particles). Think of a reactor runaway where a liquid begins to boil, or a pipeline blowdown where flashing occurs. The required discharge area (A) calculation is iterative
When a cooling failure occurs in a batch reactor, the liquid contents may flash-boil. This creates a two-phase venting stream. ISO 4126-9 provides the sizing basis for the emergency relief system. When a cooling failure occurs in a batch
Regarding two-phase flow, ISO 4126-9 offers a more prescriptive, globally-adopted approach compared to the advisory guidance in API. For multinational projects or facilities aiming for ISO compliance (e.g., ISO 9001 or ISO 45001 integration), the is mandatory.
