API RP 520 Part 1 / API Standard 521 (6th Ed.)
Only wetted area within 25 ft (7.6 m) above grade/fire base is considered. Flames can exceed 130 ft, but empirical data shows this height is adequate for relief sizing.
Critical for C coefficient calculation. Typical values: Propane 1.13, Butane 1.09, Air 1.40, Steam 1.33. Use process simulator data at relieving conditions when available.
Understand fire relief principles, calculations, and industry applications
Per API 520 Table 2: Max 21% for fire case (single device). This allows higher relieving pressure to maximize PSV capacity during external fire emergency.
API RP 520 Part 1 — Sizing, Selection, and Installation of Pressure-relieving Devices (10th Ed.)
API Std 521 — Pressure-relieving and Depressuring Systems (6th Ed., 2014)
API Std 526 — Flanged Steel Pressure-relief Valves (5th Ed.)
For preliminary sizing only. Final PSV selection requires manufacturer data and verification by qualified engineer.
• Liquid at saturation (no superheat correction Ksh=1.0)
• No rupture disk upstream (Kc=1.0)
• Preliminary discharge coefficient Kd=0.975
• Critical flow conditions (back pressure < critical)
It calculates fire case relief loads and required orifice area for pressure vessel fire exposure per API 521 standards.
Fire case relief sizing follows API 521, which specifies methods for calculating heat input and relief loads from fire exposure.
Yes, this is a free online tool for fire case relief sizing with instant results and no login required.