Casqade About
Casqade has been developed as a convenient training and screening tool. Its aim is to provide a representation of the physical effects which might occur following a release of hydrocarbon and chemical materials into the atmosphere. It can help the user by automatically joining together the mathematical models which constitute a release scenario, from initial release to final dispersion or fire effect. The mathematical models are based typically on physical principles and empirical correlations found in literature references and are described in more detail in the Casqade technical manual. Note that due to uncertainties and approximations in the models and the stochastic nature of the physical environment, the representation of a scenario might be very different to the effects observed following a real release of material in specific conditions. We consider that the outcome of a release of material will be related to the detail of the release conditions and the local physical environment, which are in general unknown to the modeller and are too complex to be accounted for in models. The benefit of models of this type lies in the ability to provide an understanding of the different physical outcomes and their possible magnitude.
The strength of the Casqade software lies in its ability to use simple input relating to the type of containment of a material and its physical conditions of temperature and pressure. The software then follows a decision tree based on these parameters to model release rate, evaporation, vapour dispersion and fire radiation and link these models in an automatic manner. The aim is to provide rapid execution of this linkage for more knowledgeable users, and to avoid major errors which can occur through mis-interpretation by less experienced users of this type of software. The software is particularly useful for training in the use of physical effect models and in potential reality checking of the results of more complex software.
Specifically Casqade includes source term models to evaluate the release rate from various containment systems. The release may be a gas, a liquid, or a two phase mixture. Evaporation and spreading of a liquid on an ideal flat surface is also modelled to give a new release rate when this is considered to be an appropriate way of developing a vapour release source. The fate of the release in the atmosphere is described as the physical effect. These physical effects include the distance associated with dispersion of vapour to a given concentration level, the distance associated with the propagation of thermal radiation to a given thermal flux level and the propagation of explosion overpressure to a given overpressure level. The effects modelled are; gas dispersion from a momentum release, gas dispersion from a release of heavy gas, a jet fire or flare thermal radiation, pool fire thermal radiation, a fireball thermal radiation and thermal dose and explosion overpressure decay.
The models in Casqade are based on an interpretation of physical models
presented by the following authors:
| Gas release rates: | General interpretation from Chemical Engineering texts including gas compressibility |
| Liquid release rates: | General interpretation from Chemical Engineering texts of the Bernoulli mechanical energy balance equation |
| Flashing liquid release rates: | The Fauske model |
| Boiling/evaporation of liquids: | The Shaw and Briscoe / Matthiessen model |
| Momentum gas dispersion: | The Ooms model |
| Heavy gas dispersion: | The Colenbrander model |
| Jet fire model: | The Chamberlain model |
| Pool fire model: | The Mudan model |
| Fireball model: | Combination TNO / Roberts model |
| Explosion model: | The TNO multi-energy model |
The current software contains a database of up to 50 single component materials available to the models. There is an option in Casqade to model multi-component mixtures using a Peng-Robinson equation of state approximation. However this is not appropriate for many multi-component mixtures due to their specific physical and chemical behaviour. Mixtures can often be represented by choosing single component materials as a surrogate for mixed materials; for example a surrogate based on molecular weight to model vapour dispersion characteristics and on heat of combustion to model fire characteristics. Further details are presented during our interactive workshops.