Estimate hazard zones for vapor cloud explosion, pool fire radiation, and flash fire scenarios using simplified TNT equivalence, point-source radiation and Gaussian plume models.
⚠ Professional Engineering Notice
Consequence modeling for siting decisions, emergency planning zones, and regulatory submissions must be performed by a qualified process safety engineer using validated QRA/consequence modeling software (PHAST, SAFETI, EFFECTS). This tool provides order-of-magnitude screening estimates only and must not be used for siting, land-use planning, or OSHA Process Safety Management documentation.
Results are screening estimates only. All consequence modeling for regulatory or design use must be performed by a qualified PE using validated software.
Screen hazard zones for vapor cloud explosions, pool fires, and flash fires. Estimate overpressure and thermal radiation distances for preliminary siting reviews and HAZOP consequence severity assessment.
VCE — TNT EquivalencePool Fire — Solid FlameFlash Fire — LFL CloudHazard Zone Diagram
⚠ Screening estimates only. Emergency planning zones, siting, and PSM documentation require validated QRA tools (PHAST, SAFETI) operated by a qualified PE.
Hazard Zones
Zone 1 — Lethal: High likelihood of fatality
Zone 2 — Injury: Serious injury probable
Zone 3 — Hazard: Detectable effects, low injury risk
Select the hazard scenario and enter release quantities
💥 Vapor Cloud Explosion
🔥 Pool Fire Radiation
🌫️ Flash Fire / VCE Cloud
TNT equivalence method: W_TNT = η × W × Hc / E_TNT. Scaled distances (Kinney & Graham TNT curve) for 140 mbar (~2 psi, partial collapse of walls and roofs), 70 mbar (~1 psi, partial demolition of houses) and 21 mbar (~0.3 psi, widespread window breakage). TNT equivalence is a rough screening method; multi-energy or Baker-Strehlow-Tang methods are preferred for congested areas.
Point-source screening model: radiated power ≈ SEP × flame surface area (2πR·Hf + πR²), spread over a sphere and multiplied by τ. Zones at 12.5, 4 and 1 kW/m², commonly used screening thresholds.
Simple Gaussian plume model for a continuous ground-level, neutrally buoyant release, using Briggs open-country dispersion coefficients (σy, σz). Dense gases such as propane or LPG spread differently and need a dense-gas model. LFL and 0.5LFL zones are indicative; crosswind width is estimated. For quantitative EPZ use PHAST/SAFETI.
Hazard Zone Distances
Select scenario above
Hazard Zone Diagram
Zone 1 — Lethal
—
—
m
Zone 2 — Serious Injury
—
—
m
Zone 3 — Hazard
—
—
m
Calculation Breakdown
⚠ Screening Use Only
Results are order-of-magnitude estimates based on simplified models. Do not use for emergency planning zones, siting decisions, or regulatory submissions without QRA by a qualified PE.
Need a Full Consequence Study or QRA?
Preliminary screening is where most engineers start — but emergency planning zones, site layouts, and PSM documentation require validated consequence modeling and a quantitative risk assessment by a qualified process safety engineer. SafeGuard Projects can help scope the study and coordinate it with a qualified consequence modeling specialist.
