DEGADIS was developed specifically to model heavier-than-air gaseous releases.

A cloud from a dense gas release behaves very differently than a plume from a lighter-than-air release. Since the gas is heavier than air, the cloud characteristics are primarily gravity-driven. Negative buoyancy and stable density stratification are among the factors that prevent the application of a Gaussian dispersion model from accurately simulating a dense gas release.

BREEZE DEGADIS can be applied to a number of scenario types, including:

• Emergency response planning
• Industrial chemicals, highly-toxic chemicals 
• Applies to a wide range of accidental release scenarios 
• Process industries that use chlorine, ammonia, LNG, and other compressed gases or cryogenic liquids
  

Release Scenarios

DEGADIS can model a number of release scenarios, including:

Release Durations

• Continuous Release: A continuous release is a steady-state release of dense gas at a constant rate into the atmosphere over a long period of time. As a rule, any release that is greater than 1,000 minutes is modeled as a continuous release. The output from modeling a steady-state release is concentration estimates at various downwind distances determined by the model.
  
• Finite Duration: A finite duration release is a steady-state release of dense gas at a constant rate into the atmosphere over a short period of time. As a rule, any release that occurs over a period of less than 1,000 minutes is modeled as a finite duration release. Finite duration model output is organized either by time or distance, depending on which parameter is of greater interest.
  
• Transient Release: A transient release varies over time; for example, if a liquid pool boils off or a container of gas depressurizes. As the pool decreases in size, the emission rate and radius change. Other transient releases include near-instantaneous releases such as container ruptures. Transient modeling output is organized either by time or distance, depending on which parameter is of most interest.

Release Method

• Vertical Jet Release: A jet release is a vertical release of a dense gas or aerosol. The simulation uses the Ooms mathematical model for a dense gas jet plume. The jet plume model requires that the jet be vertical, with a definable exit velocity. If the jet release is such that the plume centerline does not reach the ground before dispersing, the jet plume model is run alone. If this is unclear, or if the plume centerline does reach the ground, the jet plume model is run in conjunction with the regular DEGADIS model as either a continuous or finite duration release. 
  
• Liquid Spill: A liquid spill is the release of a chemical in its liquid state. The liquid is assumed to form a pool at ground level, with the evaporation rate calculated using one of three different evaporation models incorporated into DEGADIS. The results from the evaporation model are run in the DEGADIS model as either a continuous or finite duration release.

Typical Users

The typical BREEZE DEGADIS user includes:

• Plant managers
• Emergency planner and responders
• Process analyst
• PR staff 
• Plant-level EH&S 
• Students and researchers

SLAB was developed specifically to model heavier-than-air gaseous (dense gas) releases. A cloud from a dense gas release behaves very differently than a plume from a lighter-than-air release. Since the gas is heavier than air, the cloud characteristics are primarily gravity-driven.

Negative buoyancy and stable density stratification are among the factors that prevent the application of a Gaussian dispersion model from accurately simulating a dense gas release.

BREEZE SLAB can be applied to a number of scenario types including:

• Emergency response planning
• Industrial chemicals, highly-toxic chemicals 
• Applies to a wide range of accidental release scenarios and report writing

Release Types

SLAB can model a number of release scenarios, including:

Typical Users

The typical BREEZE SLAB user includes:

• Plant managers
• Emergency planner
• Process analyst
• PR staff
• Plant-level EH&S
• Students and researchers

BREEZE INPUFF is a Gaussian puff model that simulates the atmospheric dispersion of neutrally buoyant or buoyant chemical releases. The model accounts for point sources and a release duration that is either finite or continuous.

Included with the following BREEZE applications:

• Professional
• Dispersion

AFTOX was developed to model neutrally buoyant gas releases and liquid spills that evaporate to a neutrally buoyant gas. Gas releases are limited to those that are neutrally buoyant (non-dense, non-buoyant) with no velocity, and emanating from a point (non-area) source. Liquid spills are limited to single-phase releases of low volatility liquids.

Industrial chemicals, highly-toxic chemicals, and emergency response planning applies to a wide range of accidental release scenarios and process analysis.

Typical Users

The typical BREEZE AFTOX user includes:

• Plant managers
• Emergency planner
• Process analyst
• PR staff
• Plant-level EH&S
• Students and researchers

BREEZE Expert

BREEZE Expert is a proprietary model developed by BREEZE to calculate source-term parameters needed by accident release dispersion models.  Both source-term and non-source-term models require observable data to perform calculations. The only difference is whether you or the model perform the calculation of input release conditions.

Included with the following BREEZE applications:

For BREEZE Expert, the following information is required:

• Chemical
• Storage temperature
• Storage pressure
• Hole size
• Depth of liquid in container above hole
• Maximum pool size
• Meteorological conditions

The calculations performed by BREEZE Expert are designed to provide input to non-source-term models including those in the BREEZE HAZ suite of dispersion models (i.e., DEGADIS, SLAB, INPUFF, and AFTOX). BREEZE Expert requires information about the following physical aspects of the release scenario:

• Vessel shape and dimensions
• Release location and orientation
• Diking
• Chemical database
• Release class
• Release duration, either specified by the user (reaction time) or computed by BREEZE Expert

BREEZE Expert calculates the key model input parameters (e.g., pool evaporation rate, emission rate, etc.) based on user-specified observables such as chemical property data and storage, release, and ambient meteorological conditions. It then recommends an appropriate dispersion model based upon the calculated results and seamlessly transfers these results to the dispersion model. The algorithms in BREEZE Expert are based primarily upon the EPA's document entitled "Guidance on the Application of Refined Dispersion Models to Hazardous/Toxic Air Pollutant Releases", April 1993.

Applicability

BREEZE Expert is designed to perform the source-term analysis portion of an off-site consequence analysis. Users can enter the known conditions of the release and the source-term parameters that are required to run the dispersion models in BREEZE HAZ will be automatically calculated.

The initial step in preparing the input required for any air release model is to gather the observable data; the release’s physical description prior to and at the time of the release. There are two types of models: source-term and non-source term. BREEZE Expert is a source-term model that estimates the gas state of a release entering the atmosphere. It calculates the injection of the gas into the atmosphere and, as gases cool during depressurization, any aerosol that might form to expansion cooling.

In addition to the emission rate, BREEZE Expert also calculates temperature, initial concentration, and initial density parameters. It also calculates the emission rate of a liquid release from a container, and the rate of the gas and aerosol injection into the atmosphere. Non-source term models are models that cannot calculate release conditions based on storage conditions. BREEZE HAZ DEGADIS, SLAB, INPUFF, and AFTOX are non-source-term models that rely on user-defined release conditions. These calculations are performed outside the model. The non-source term model then uses a dispersion algorithm to estimate impacts based on the user-calculated input. These calculations are often very complex and subject to error if extreme care is not used in their derivation. BREEZE Expert eliminates the potential for error, to a large degree, and quickly generates appropriate input to non-source term models.