BREEZE - The World Leader in Air and Haz Dispersion Models for over 25 years

BREEZE HAZ SLAB Dense Gas Modeling SoftwareSLAB

BREEZE HAZ SLAB, a software package used to model the dispersion of an accidental chemical release resulting in a neutrally buoyant or denser-than-air plumes.  This package includes the SLAB model, developed by Lawrence Livermore National Laboratory, and BREEZE's proprietary source-term model, EXPERT.  The software is ideal for emergency planning and response and for meeting the requirements under the Environmental Protection Agency's (EPA's) Risk Management Plan (RMP).

SLAB is a dispersion model that is used to determine the downwind distance to toxic threshold concentrations or flammability levels from accidental chemical releases.  The release scenarios can be instantaneous, finite, or continuous in duration.  Allowable source types include evaporating pools, horizontal and vertical jets, stacks, and instantaneous area sources.  Averaging times can be on the order of seconds and upwards to an hour.

Except for the evaporating pool source, which is assumed to be all vapor, all of the remaining sources are either pure vapor or a mixture of vapor and liquid droplets (aerosol).  Transport of the vapor-aerosol mixture is treated as a single fluid and neglects ground deposition of the aerosol.  The thermodynamics of aerosol formation and evaporation for both the released chemical and ambient water vapor is treated by assuming local thermodynamic equilibrium.

For a continuous release, SLAB assumes steady-state conditions and calculates the average concentration as a function of downwind distance from the source.  For a finite duration or instantaneous release, the model provides estimates of concentration as a function of downwind distance from the source and plume travel time.  In all cases, the spatial distribution of the plume in the crosswind and vertical direction are calculated.

EXPERT is a source-term model that is used to calculate certain source parameters, such as evaporation rate, pool radius, or release duration, that are needed to run the SLAB model.  EXPERT automatically calculates the required source-term parameters and seamlessly transfers the results to SLAB, where they are used as model input.


BREEZE HAZ SLAB offers many features to tailor your analyses to a wide variety of sources and release scenarios.

 Release Scenarios... models a variety of release scenarios, including: gas and aerosol releases; continuous, instantaneous, and finite duration; evaporating pools; vertical and horizontal jets; stacks.

 Receptors... calculates plume concentration at model-selected downwind receptor distances.

 Chemical Property Data... contains a database of over 150+ common industrial chemicals. The program includes the capability to add and store new chemicals or modify existing chemical data.

 Toxicity Data... includes chemical toxicity data, including the Toxic Endpoint, IDLH (Immediately Dangerous to Life and Health), TLV-TWA (Threshold Limit Value - Time Weighted Average), and TLV-STEL (Threshold Limit Value - Short Term Exposure Limit) values, where available, for each chemical.

 Meteorological Data... estimates stability class using site characteristics, date and time of release, and user-specified cloud cover, cloud type, and wind speed observations or the stability class can be entered directly. The model simulates one set of meteorological conditions, and is applicable for averaging periods of 1-hour or less.