Introduction:

Fire and Explosion Risk Assessment (FERA) is a detailed, consequence-focused study that evaluates the specific hazards posed by potential fires and explosions within a process facility. It moves beyond simply identifying that a fire or explosion could happen (as in HAZID) to quantifying its potential effects in terms of heat radiation, overpressure, and blast loads. FERA is often a key component of a broader Quantitative Risk Assessment (QRA) or a standalone study to inform design for fire protection and mitigation.

Purpose:

The purpose of FERA is to understand the physical effects of postulated fire and explosion incidents to enable effective risk mitigation. Its objectives are to: 

1) Model the potential consequences of identified flammable release scenarios (e.g., jet fire, pool fire, flash fire, vapor cloud explosion), 

2) Determine the hazardous ranges (e.g., distance to specific radiation levels or overpressure contours), 

3) Assess the impact on people, structures, and critical equipment, and 

4) Provide the technical basis for specifying active and passive fire protection systems, blast-resistant design, and emergency response plans.

Methodology:

FERA is conducted in a structured sequence:

1.  Scenario Selection: Identify credible fire and explosion scenarios from HAZOP/PHA and dispersion analysis (e.g., high-pressure gas jet fire, large pool fire from a tank rupture, vapor cloud explosion from a congested area release).

2.  Source Term & Release Modeling: Define the release rate, duration, and fluid properties.

3.  Consequence Modeling:

    Fire Modeling: Use empirical or CFD models to calculate flame size, duration, and thermal radiation levels at various distances (e.g., for jet fires, pool fires, fireballs).

    Explosion Modeling: For vapor clouds, use phenomenological models (TNO Multi-Energy, Baker-Strehlow-Tang) or advanced CFD to predict explosion overpressure as a function of distance, accounting for congestion and confinement.

4.  Impact Assessment: Compare the calculated effects (e.g., 37.5 kW/m² radiation for structural damage, 0.3 barg overpressure for serious injury) against the location of personnel, buildings, and equipment to determine potential harm.

5.  Recommendations: Propose risk reduction measures such as improved spacing, fire walls, deluge systems, blast walls, or design changes to reduce inventory or congestion.

Importance in the Process Industry:

FERA is essential for moving from qualitative hazard awareness to quantitative engineering decisions about fire and explosion protection. In an industry where hydrocarbons are the primary feedstock, the risk of fire and explosion is omnipresent. FERA provides the scientific basis for designing facilities that can withstand or mitigate these events. It ensures that firefighting systems are correctly sized, that critical control buildings are sited or hardened appropriately, and that the overall plant layout minimizes escalation potential. It is a fundamental tool for demonstrating that risks are ALARP and for protecting both assets and human life.