Fire & Explosion Risk Assessment (FERA)

The need for FERA

Where the cost of CFD modelling is not possible or appropriate, Elixir can carry out gas dispersion or consequence modelling using DNV Phast software. Scenarios are selected based upon common leaks, worst case leaks and any other scenarios which may be specified by our client. This modelling reviews the dispersion of flammable gas with respect to possible explosive accumulations and aids in safety reviews as well as validating any Fire and Gas detection and protection measures proposed or already in place.

Many scenario based models can be misleading and dangerous if applied alongside F&G detection mapping without a broad knowledge of the principals behind both consequence analysis and Fire and Gas detection design. Using the scenarios in a safe and robust way is the key to ensure the design is optimised but not at the expense of safety.

DNV Phast is one of the most comprehensive process industry hazard analysis software tools for all stages of design and operation. The software examines the progress of a potential incident from the initial release to far-field dispersion including modelling of pool spreading and evaporation, and flammable and toxic effects.

Although the modelling is done computationally, all outputs are cross-checked by our subject matter experts calculations which give a estimated figure for each individual output. This gives reassurance that the semi-quantitative model is accurate and reflective of the input data.

The primary need for a FERA study are as follows:

• Identify fire and explosion hazards on the facility that may pose a risk to personnel, affect the facility equipment and may escalate to other parts of the facility;
• Quantification of fire and explosion risks arising from loss of containment;
• To determine the acceptability of the calculated fire and explosion risk at the facilities and identification of the key fire and explosion risk contributors. Risk contributors need to be identified by source and location;
• Assess the benefit of existing and possible, inherently safe, prevention, detection, control and mitigation measures for identified fire and explosion scenarios;
• Comparing fire and explosion risks of the design options being considered. This helps identifying design options with low risk, and selecting the option which is best from a risk
• For a Brownfield project the purpose of the FERA is to assess the new fire and explosion risks due to plant modification and to arrive at the cumulative risk of the new and existing facilities. In such a project the risk from the new facilities will not be assessed separately, it will be assessed in relation to the existing risk at the facility, and in particular the process facilities adjoining to the new facilities;
• To provide clear and unambiguous recommendations for risk reduction where necessary, to ensure that the facilities fire and explosion risks are controlled within acceptable limits.

The FERA Process flowchart is used as a framework for this guideline and to serve as a basis for the minimum requirement for a FERA study undertaken by a FERA specialist.

The FERA process essentially consists of;

• Identification of events which could cause fires or explosions;
• Analysis of frequencies of these events based on generic failure data;
• Modelling of event consequences, in terms of fire size, explosion damage and subsequent escalation;
• Recommending suitable means of preventing, detecting, controlling and mitigating fire and explosion events.

FERA Methodology

The FERA considers accidental releases from equipment’s carrying flammable & hazardous inventory. Normal design operation of the isolation system is assumed when determining the duration and characteristics of releases. Dust release rates and duration shall calculate based on normal operating pressures and process conditions.

The consequence analysis determines the size and duration of releases and predicts hazard zones for releases in terms of radiant heat. FERA evaluates the adequacy of fire protection system and recommends risk reduction measures based on the consequence results.