DEGADIS accounts for ground-level area and vertical jet releases that may be either finite or continuous in duration. For a vertical jet release, the Ooms model is used to predict the trajectory and dilution of the gas or aerosol and DEGADIS predicts the ensuing ground-level concentrations after the plume has returned to ground.
DEGADIS also has the unique capacity to model both of these source types as transient releases, where the emission rate and source dimensions vary with time. DEGADIS can account for heat transfer between the plume/ambient air interface and plume/ground interface.
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 Type |
Duration |
Ground-level
|
• Continuous
• Finite
• Transient
|
Vertical Jet
|
• Continuous
• Finite
|
Evaporating Liquid Spill
|
• Continuous
• Finite
• Instantaneous
|
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