Flare Thermal Radiation & Sterile Zone Calculator (API 521)
Determine grade thermal radiation intensity ($K$, kW/m²), flame wind deflection, and personnel exclusion zone radius according to API Standard 521.
Flare Stack & Gas Release Rate
Exclusion Radius & Grade Intensity
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API Standard 521 Flare Sizing Criteria
API Standard 521 governs the design and sizing of pressure-relieving and flare disposal systems in petroleum refineries and petrochemical plants. The fundamental safety constraint governing flare stack height and plant layout is grade-level thermal radiation.
Permissible Radiation Exposure Levels
API 521 Table 5 outlines maximum design thermal intensities (including solar radiation):
• $1.58\text{ kW/m}^2$ ($500\text{ BTU/hr-ft}^2$): Maximum for continuous, unrestricted personnel exposure without protective clothing.
• $4.73\text{ kW/m}^2$ ($1500\text{ BTU/hr-ft}^2$): Maximum for areas requiring emergency personnel escape within 30 seconds.
• $9.46\text{ kW/m}^2$ ($3000\text{ BTU/hr-ft}^2$): Maximum for uninsulated steel structures and storage tanks.