When a pressure relief valve opens or an emergency blowdown occurs, the released hydrocarbon inventory can disperse and, if ignited, generate harmful thermal radiation. Vent Dispersion & Thermal Radiation analysis evaluates these release effects and defines safe boundaries for personnel, equipment, buildings, and operating areas.
At iFluids, we provide regulatory-grade studies for oil & gas, petrochemical, LNG, upstream, midstream, and downstream facilities, using defensible modelling methods, site-specific meteorological data, and alignment with API 521, ISO 23251, and applicable local regulations.
What Is a Vent Dispersion & Thermal Radiation Study?
A Vent Dispersion & Thermal Radiation Study is a quantitative consequence modelling exercise used to predict how hydrocarbon releases behave after discharge from vents, flare systems, pressure relief devices, rupture discs, or blowdown systems. It provides a clear understanding of how released process fluid interacts with the environment and what risks it creates to people and assets.
The study is typically divided into two key technical components:
- Dispersion Analysis
Evaluates the spread of flammable gas clouds based on:- Release conditions (pressure, temperature, inventory)
- Wind speed and direction
- Atmospheric stability class
- Buoyancy and release momentum
- Terrain and surrounding obstructions
- Thermal Radiation Analysis
Assesses heat exposure from ignited releases by:- Calculating radiation intensity in kW/m²
- Determining impact on personnel, equipment, and structures
- Defining safe exposure limits and emergency response distances
Together, these Vent Dispersion & Thermal Radiation analyses enable engineers to define safe separation distances, exclusion zones, and layout decisions, ensuring overall process safety compliance and protection of personnel and critical infrastructure.
PHAST → Simulates physical effects such as gas dispersion, thermal radiation and explosion impact
SAFETI → Utilizes consequence modelling results to evaluate overall risk levels
Why Regulatory Bodies Mandate This Analysis
Regulatory bodies require Vent Dispersion & Thermal Radiation analysis because vent and flare releases can directly affect personnel safety, equipment integrity, and facility siting. Standards such as API 521 and ISO 23251 require vent and flare system designs to consider thermal radiation impact at grade level and nearby equipment.
For LNG facilities, NFPA 59A also defines dispersion and radiation criteria for safe siting of process equipment and occupied areas. Without a proper Vent Dispersion & Thermal Radiation study, facilities may place control rooms, muster areas, access routes, or critical equipment within hazardous zones, creating both safety and compliance risks.
Core Services We Deliver
iFluids delivers complete Vent Dispersion & Thermal Radiation studies, covering dispersion modelling, radiation impact analysis, exclusion zone definition, and regulatory reporting. Each study is customized to the facility layout, release conditions, meteorology, and applicable codes.
- Atmospheric Dispersion Modeling
We model gas cloud movement and define LFL / half-LFL zones based on release conditions, wind, stability class, and gas behavior.
- Thermal Radiation Flux Analysis
We calculate heat flux levels in kW/m² for ignited releases and map radiation contours to assess personnel, equipment, and structure exposure.
- Exclusion Zone & Safe Separation Distance Determination
We define safe distances, ignition control zones, and vent height/orientation requirements to support layout safety and compliance.
- Emergency Blowdown & Depressurization Venting Studies
We assess time-varying releases during blowdown or depressurization to determine the full dispersion and radiation impact envelope.
Vent Dispersion & Thermal Radiation Methodology
Our methodology follows a structured four-step approach aligned with API 521, ISO 23251, and project-specific safety requirements, ensuring technically robust and regulatory-compliant outcomes.
Step 1 — Source Term Definition & Scenario Development
We establish realistic release scenarios using actual process data rather than assumptions. This includes defining operating conditions, fluid properties, vent characteristics, and credible worst-case scenarios that drive the overall study accuracy.
Step 2 — Dispersion Modeling & Meteorological Data Integration
Using site-specific weather conditions, we simulate how the released process fluid disperses in the atmosphere. This helps generate LFL and half-LFL contours, identify downwind distances, and evaluate potential impact zones within the facility layout.
Step 3 — Radiation Heat Load Calculation & Consequence Mapping
For ignited scenarios, we assess thermal radiation levels and map their impact on personnel, equipment, buildings, and critical access routes. This step defines exposure levels and supports safe design decisions.
Step 4 — Deliverables, Reporting & Regulatory Submission
We compile the results into regulatory-ready reports that include modelling assumptions, dispersion and radiation contours, exclusion zones, compliance checks, and clear engineering recommendations for safe and optimized facility design.
Compliance Standards & Codes
Our Vent Dispersion & Thermal Radiation studies are aligned with key international and local process safety standards for vent design, dispersion modelling, thermal radiation assessment, and exclusion zone definition.
| Standard / Code | Scope | Application |
| API 521 | Pressure-relieving and depressuring systems | Relief system design, vent stack assessment, radiation criteria |
| ISO 23251 | Pressure-relieving systems for petroleum and gas industries | International equivalent guidance for API 521-based assessments |
| API 505 | Pressure-relieving device installation guidance | Supplementary relief system design support |
| NFPA 59A | LNG facility safety | Dispersion and radiation siting criteria for LNG facilities |
| IP Model Code Part 15 | Petroleum area classification | Flammable cloud and hazardous zone definition |
| IEC 60079-10-1 | Explosive gas atmosphere classification | Hazardous area zone boundary assessment |
For local regulatory requirements such as PESO, HSE, ADNOC CoPs, or client-specific standards, we align the methodology and report format accordingly.
Industry Applications
Vent Dispersion & Thermal Radiation studies support safety and compliance for:
- Refineries & Petrochemical Plants – Relief, vent, and flare system impact assessment
- Offshore Platforms & FPSOs – Personnel, escape route, and equipment exposure evaluation
- LNG & Gas Processing Facilities – Dense gas dispersion and safe siting assessment
- Brownfield Modifications – Layout validation during expansion or equipment replacement
Why Engineering Teams Choose Us
Engineering teams choose iFluids Engineering and Consultancy WLL for Vent Dispersion & Thermal Radiation studies because our work is led by experienced process safety engineers, not generated from standard templates. We use PHAST for regulator-accepted consequence modelling and apply CFD simulation only when complex layouts require a more defensible approach.
Our reports are structured to support:
- HAZOP and HAZID reviews
- Regulatory submissions
- Practical design decisions
This ensures every Vent Dispersion & Thermal Radiation study is technically sound, review-ready, and directly applicable to real facility safety improvements.