The Chad Risk Assessment

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Abo Homos-Nubaria Pipeline QRA

Consequence Modelling Results

In order to perform consequence modelling analysis of the potential hazardous scenarios resulting from loss of containment, some assumptions and design basis have been proposed.

the pipeline release orientation have been proposed to be a vertical release, which is considered for buried underground pipeline releasing the entrapped materials in the vertical direction upwards (represents the actual release scenario). Other release orientations represent the exaggerated release scenario.

For the pipeline leak scenario, the release rate has been simulated based on 3-hole sizes as follows:

•Full bore rupture (32-inchs);

•Half bore rupture (16-inches);

•Pin hole leak (1-inch).

The first leak size is a full bore rupture of the pipeline (32 inch leak), which presents a hole diameter equivalent to the pipeline diameter. This scenario presents the worst case scenario for maximum release rate in order to represent a catastrophic release scenario.

The second leak size is a half bore rupture of the pipeline (16 inch leak), which presents a hole diameter equivalent to half the pipeline diameter. This scenario presents the severe case scenario for a reduced release rate in order to represent a major release scenario.

The third leak size is a one inch hole in the pipeline (1 inch leak), which presents a pin hole in the pipeline wall or small deformation equivalent to the one inch hole in diameter. This scenario presents the mild case scenario for a reduced release rate in order to represent a minor release scenario.

FRED has been selected for the consequence modeling of different types of hazardous consequences modeling presented as follows:

•Jet fires (resulting from immediate ignition).

•Gas clouds and Flash fires (resulting from delayed ignition),

Weather conditions have been selected based on wind speed and stability class for the greater Cairo area detailed weather statistics.

The worst case weather conditions for gas dispersion is the stable weather conditions, represented by wind speed of 2 m/s and stability class "F" representing "Very Stable" weather conditions, in order to obtain conservative results.

The gas dispersion distances have been calculated in meters in concentration terms of Lower Flammability Limits (LFL) and Upper Flammability Limits (UFL) presented by Part Per Million (PPM) concentrations in order to represent the flammability range of the released gas cloud; however the extent of damage is presented by LFL only.

Abo Homos-Nubaria Pipeline QRA

The heat radiation from flash fires will not significantly affect humans, equipment or structures outside the 12.5 (Kw/m2) heat radiation envelopes due to the short duration of flash fires [in terms of milliseconds].

Since the jet fire is originally a high momentum directed jet release, hence the effects of wind direction, wind speed or atmospheric stability on the jet flame are minimal.

The jet fire (flame length) and heat radiation distances are measured in meters.

The extent of harmful effects on humans is presented by the distance to the heat radiation contour of 12.5 (Kw/m2) and the extent of damage for equipment is presented by the flame length (frustum).

The following figures present the gas cloud distances in meters which consequently represent the extent of damage distances to the LFL for different pressure profiles, different release orientations and different leak sizes (release rates), as a result from the consequence modelling simulation analysis performed.

Since the gas is heavier than air, the released plume tends to disperse on the ground level depending on the weather conditions of the area, which in general is more likely to meet an ignition source leading to flash fire.