Quoted from: https://www.cerc.co.uk/environmental-software/GASTAR-model.html 

What is GASTAR?

GASTAR is a dense gas dispersion model developed by CERC ideally suited to modelling accident and emergency response scenarios or investigating site safety involving releases of flammable and/or toxic materials from a variety of industrial accidents such as cryogenic spills, catastrophic tank failure, pipe fractures and multi-phase jets.

GASTAR is used for:

• risk assessment,
• land-use planning,
• emergency response planning,
• management and training.

GASTAR is an integral (or box) model. Using a combination of conservation laws applied to the cloud, supplemented by semi-empirical relations derived from dispersion research, it calculates spatially-averaged properties of the cloud, and their variation with distance downwind, and then applies profiles to give the concentration at any point. Novel features, such as slopes and obstacles, are incorporated into the integral formulation. Efficient solution algorithms require only seconds to solve a typical problem.

The application is simple to use, with a well-designed user-friendly Windows interface similar to other CERC models, simplifying input data entry and providing flexible examination of output. GASTAR is also supplied with a database of material properties for common toxic and flammable substances; further substances can be added by the user as required.

Who uses GASTAR?

GASTAR was developed in association with the UK Health and Safety Executive (HSE), with specialised features used by RISKAT, the HSE's Risk Assessment Tool. In addition, GASTAR has been used by consultants in studies, both in the United Kingdom and elsewhere, including LNG spills, flammable hydrocarbon waste jets and site safety planning.

Why use GASTAR?

In brief, GASTAR

• models cloud evolution from denser-than-ambient to passive conditions,
• models puffs, plumes and transient releases,
• includes a 2-phase fully 3-dimensional jet source model,
• includes a pool uptake model for advection of material from liquid spills,
• accounts for complex effects such as slopes and obstacles,
• is a fast-executing Windows application.

In addition to standard features, such as continuous plume and instantaneous puff releases and momentum jet sources, dense and neutral releases, GASTAR includes many novel features, such as the effects of terrain (variable slopes and ground roughness) and obstacles (fences and buildings, which may be porous), a pool uptake model (GASTAR interfaces with CERC's comprehensive pool spill model LSMS), time-varying releases and a jet that may point in any direction. In general, other denser-than-ambient dispersion models only include a subset of these features.

Results from GASTAR can be viewed graphically using the built-in graphics tool or in tabular form via the interface. Output from each run includes a summary of the input data and output for all calculated cloud properties at any specified time. Additionally, a wide range of derived output is available, such as concentration-time histories at any (x, y, z) location and, as appropriate, characteristics of the lower flammability limit (LFL) contour, flammable volume and mass, dose and toxic load.