Studies on the effect of the fire suppression on compartment fires

Ndlovu, Shephard (2022) Studies on the effect of the fire suppression on compartment fires. Doctoral thesis, University of Central Lancashire.

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The effect of fires in compartments present unique danger and can result in significant loss of life, loss of property and damage to the environment. Fire safety is achieved by means of passive fire protection provisions, reduction of fire load and prevention of the fire spreading from one compartment to another. The main design goals are to prevent fires from starting; to detect, control and extinguish those fires that occur, thus, limiting the damage and minimising its effects on systems performing essential safety functions. There are several ways to carry out the above suggested analysis, one way is carrying out large scale physical experiments that accurately account for such complex phenomenon. This tends to be very expensive and use of computer fire models is preferred where fires are modelled, and their behaviour can be predicted without the need for expensive full-scale experiments. Automatic fire sprinklers have been used successfully to protect life and building structures from the disruptive nature of fire and have significantly contributed to the reduction of loss from fires.

In buildings, the fire development can lead to flashover, which presents a danger to both occupants and fire fighters. Fire sprinklers can be used to avert the probability of flashover occurring and this can be achieved by designing and installing fire sprinkler system in buildings. The first part of the research focuses on the comparison between the model and experimental results ranging from small, medium, and large scale. A simplified methodology for predicting time to flashover is outlined and comparison with experimental data was conducted. The validation of the model with the experimental data has been carried out and having compensated for errors in timescale, an improved semi-empirical formula has been presented.

The research goes on to focus on the problem of fire suppression by sprinklers. The application of zone model and Computational Fluid Dynamics (CFD) modelling methods to sprinkler design remains a challenge due to sophistication of the models currently available and the limited amount of validation data. This work combines the three methods, that is, provide large-scale data to validate the zone model and CFD techniques. A proposed zone model, which assumes that a fire starts at some small non-zero size and growing radially over a flat, solid/liquid fuel, for a small fire on a flat piece of solid fuel with the cone-shaped flame has been applied. A comparison between the Quantified Sprinkler Actuation Time (QSAT) model and large-scale experiments is conducted; It was found that the QSAT model gave reasonable predictions of the sprinkler actuation time in 70% of experimental data from which the analysis were derived. Further comparison with Fire Dynamic Simulator (FDS), the data show that there is a reasonably good correlation between the experimental and sprinkler zone model while in all cases, the FDS model predicts quicker sprinkler actuation times.

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