Consequence vs lethality footprints

Understanding the distinctions between consequence and lethality footprints is crucial as each type is defined by different parameters and treated differently within RISKCURVES. This article describes the different types of consequence and lethality footprints in RISKCURVES and when to use them.

It is important to realise that these footprint definitions were made available within RISKCURVES before:

• The import of footprints from other consequence modelling software using a template Excel spreadsheet was introduced in RISKCURVES v12.

• Copy-Pasting models from EFFECTS to RISKCURVES was possible. Note that all EFFECTS single and combined models are available within RISKCURVES, allowing users to see not only risk results, but also consequence results. For more information about this process, refer to the article Adding a model in RISKCURVES.

Although there are now more efficient methods available, this functionality is still accessible for those who prefer to perform their QRAs in this manner.

Consequence footprints

Consequence footprints calculate the probability of exceeding physical thresholds, aiding in the assessment of consequence risk. There are different types of consequence footprints available in RISKCURVES, including explosion, fireball, pool fire, jet fire, and toxic dispersion.

Explosion consequence definition

• Key parameters:

  • Flammable cloud size

  • Overpressure offset

  • Distance vs. overpressure data

• Examples: The explosion consequence definition can assess a Vapour Cloud Explosion or Flash Fire + Vapour Cloud Explosion. See these two examples below.

  • Non-flammable local explosions

    • Models in EFFECTS: Vapour Cloud Explosion, BLEVE Blast, Gas Blast, and Rupture of Vessels. These phenomena lead to the generation of a blast wave but do not produce a flammable vapour cloud.

    • Parameters:

      • Set “Offset explosion centre” to 0. That is because for these phenomena, the hazardous chemical does not drift away, as it consists of a localized explosion. The centre of the explosion centre is at the release point.

      • Set ‘‘Fraction with explosion phenomena’’ to 1.

      • Fire result section parameters set to 0, as no flame dimensions are needed for these explosions without flammable cloud.

• Flash Fire + Vapour Cloud Explosion

  • Models in EFFECTS: Flammable Dispersion.

  • Parameters:

    • Use “Offset explosion centre” for cloud drift, accounting for the flammable cloud travelling along wind before igniting.

    • Calculate ‘‘Fraction with explosion phenomena’’ based on congested area overlap. For more information refer to the article about how to define 3D congestion areas.

    • Fire results define flame area.

    • Min. distance defines the boundary of the flame envelope.

• Lethality determination: Defined by overpressure levels in Vulnerability settings (e.g., 300 mbar = total destruction). Note that the probability of combined heat radiation and overpressure levels is defined by the "Fraction with explosion phenomena" (available in the Frequencies and probabilities node).

The image below shows how the explosion footprint is defined when the pressure damage translation is based on “Threshold pressure level”. This will produce two contours: one for total destruction zone (300 mbar), and another for interior damage from glass fragments (100 mbar).

BLEVE and Gas Fireball consequence definition

• Key parameters:

  • Radius of the fireball

  • Duration of the fireball

  • Heat radiation vs distance from the flame centre

• Exclusions:

  • Overpressure damage is not included for flammable effects. For non-flammable BLEVEs, use the Consequence defintion - Explosion.

• Example: BLEVE Fireball

  

• Lethality determination:

  • Heat radiation levels and probits defined in vulnerability settings.

  • Default total destruction level is 35 kW/m².

  • Independent of wind speed and Pasquill stability class.

Pool or Jet Fire consequence definition

• Key parameters:

  • Heat radiation vs distance

• Example:

  • Horizontal Jet Fire: Positive offset

  • Pool Fire: Negative offset

  • Shifts the flame's tail concerning the release point

• Lethality determination:

  • Heat radiation levels and probits defined in vulnerability settings.

  • Default total destruction level is 35 kW/m².

Toxic consequence definition

• Key Parameters:

  • Contour dimensions for specific concentration thresholds.

• Requirements

  • Specific chemical selection.

  • Exposure duration for lethality translation.

• Example: Toxic cloud

• Lethality Determination:

  • Defined by choices in vulnerability settings (fixed ratio or using a ventilation rate).

  • Indoor lethality: Applies only to Societal Risk.

Lethality footprints

Lethality footprints define known lethal effect area. Similar to consequence footprints, there are various types available in RISKCURVES, including explosion, fireball, pool fire, jet fire, and toxic dispersion.

Explosion lethality definition

• Key parameters

  • Radius pressure level for total destruction

  • Radius pressure level for inside damage

  • Offset explosion centre

  • Heat radiation lethality vs distance

• Examples: Can also be assessed for a Vapour Cloud Explosion or Flash Fire + Vapour Cloud Explosion, as explained in “Explosion consequence definition”, using lethality levels instead of overpressure levels.

  

• Lethality determination: Defined the same way as described for “Explosion consequence definition”.

BLEVE or Gas Fireball lethality definition

• Key parameters:

  • Radius of the fireball

  • Radius of peak overpressure

  • Radius of 35 kW/m²

  • Fraction of lethality vs. distance from flame centre

• Lethality determination

  • Within this radius of the fireball = 100% lethality.

  • Within the peak overpressure radius = 100% lethality.

  • Within radius of 35 kW/m² = 100% lethality.

  • Independent of wind speed and Pasquill stability class.

Pool or Jet Fire lethality definition

• Key parameters:

  • Heat radiation lethality vs distance

• Example: Same as for Pool or Jet Fire consequence definition, but the footprint dimensions are defined based on lethality.

  

• Lethality determination:

  • Calculated based on people within the flame envelope.

  • Follows the lethal fraction in the flame contour as per vulnerability settings.

Toxic lethality definition

• Key parameters:

  • Outside and inside toxic lethality vs distance table

• Example:

• Lethality determination:

  • Outdoors: Defined for outdoor areas.

  • Indoors: Used for Societal Risk calculations, determining victims inside houses, not considered for Individual Risk. Determined by choices in vulnerability settings (fixed ratio or using a ventilation rate).