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Developing tactics for extinguishing fires located in civil structures is needed. Nowadays, the most commonly procedure employed by most fire brigades when extinguishing fires located in the interior of buildings, consists in sending a unit of firefighters inside the structure spraying water on the surface of the burning fuels. This procedure has enormous caveats since it leads to the unavoidable necessity of exposing personal to situations where risks to their personal safety are major. An alternative to these tactics consists on using the Cutting extinguisher which in principle allows combating a fire by injecting water mist into the burning building without the necessity of entering it. This work studies the capabilities and limitations of the Cutting extinguisher when used for fire-fighting activities in conventional and idealised civil structures by the aid of computerised simulations and experimental data. The simulations were done using Fire Dynamics Simulator (FDS) which is an open-source code for modelling well-ventilated fires while experimental data was obtained from idealised and controlled fires and experiments. Findings of this study suggest that the Cutting extinguisher is effective for combating fires of moderated size in confinements using less water than traditional methods by reducing the relative concentration of oxygen in the room instead of by cooling the fuels as traditional methods do. The high velocity of the jet induces mixing in the confinement, enhancing the interaction of droplets with hot combustion products and promoting the vaporisation of the injected water. Furthermore, the induced momentum to the gases in the room together with the vaporisation of the injected water reduces the overall gas temperature inside the structure.

Developing tactics for extinguishing fires located in civil structures is needed. Nowadays, the most commonly procedure employed by most fire brigades when extinguishing fires located in the interior of buildings, consists in sending a unit of firefighters inside the structure spraying water on the surface of the burning fuels. This procedure has enormous caveats since it leads to the unavoidable necessity of exposing personal to situations where risks to their personal safety are major. An alternative to these tactics consists on using the Cutting extinguisher which in principle allows combating a fire by injecting water mist into the burning building without the necessity of entering it. This work studies the capabilities and limitations of the Cutting extinguisher when used for fire-fighting activities in conventional and idealised civil structures by the aid of computerised simulations and experimental data. The simulations were done using Fire Dynamics Simulator (FDS) which is an open-source code for modelling well-ventilated fires while experimental data was obtained from idealised and controlled fires and experiments. Findings of this study suggest that the Cutting extinguisher is effective for combating fires of moderated size in confinements using less water than traditional methods by reducing the relative concentration of oxygen in the room instead of by cooling the fuels as traditional methods do. The high velocity of the jet induces mixing in the confinement, enhancing the interaction of droplets with hot combustion products and promoting the vaporisation of the injected water. Furthermore, the induced momentum to the gases in the room together with the vaporisation of the injected water reduces the overall gas temperature inside the structure.

The vibrational energy of water droplets has been investigated. Viscosity was neglected and only the lowest order symmetrical vibration, the quadrupole mode with m=0, was considered. An approximative solution was given by Rayleigh in 1879: w_vib=2a^2 ??r_0?^2 where ? is the relative vibration amplitude, ? is the surface tension, and r0 is the droplet radius at equilibrium, that is the radius of the spherical droplet. It was found that this solution agrees with the exact solution within a few percent for moderate values of the relative amplitude ?. The rationale of this study was to investigate whether dissipation of energy from a shock wave, e.g. from an explosion, into vibrational energy of droplets is a mechanism that needs to be considered on order to accurately model explosion mitigation using water mists. Traditionally droplet vibrations are not considered in such models whereas other mechanisms such as translational energy, heating, evaporation, and droplet breakup are considered. A useful parameter for quantifying the relative importance of vibrations as compared to linear acceleration of droplets is the ratio between vibrational and translational kinetic energy. This ratio is given by 3a^2 ?/(?p?r_0 v?_transl^2 ) where vtransl is the translational velocity to which the droplet has been accelerated by the shock front. This ratio is negligible for a particular severe explosion scenario where information on vtransl was available in the literature. For other cases vibrations might be of some significance but detailed information about the specific scenarios is needed to obtain detailed results. More work is needed in order to understand the effect of viscosity and higher order vibrations. Furthermore a model for the excitation of droplet vibrations by shock waves is required for modelling. Finally there is a lack of experimental knowledge on droplet size distribution for water mist interacting with a shock wave.

The vibrational energy of water droplets has been investigated. Viscosity was neglected and only the lowest order symmetrical vibration, the quadrupole mode with m=0, was considered. An approximative solution was given by Rayleigh in 1879: w_vib=2a^2 ??r_0?^2 where ? is the relative vibration amplitude, ? is the surface tension, and r0 is the droplet radius at equilibrium, that is the radius of the spherical droplet. It was found that this solution agrees with the exact solution within a few percent for moderate values of the relative amplitude ?. The rationale of this study was to investigate whether dissipation of energy from a shock wave, e.g. from an explosion, into vibrational energy of droplets is a mechanism that needs to be considered on order to accurately model explosion mitigation using water mists. Traditionally droplet vibrations are not considered in such models whereas other mechanisms such as translational energy, heating, evaporation, and droplet breakup are considered. A useful parameter for quantifying the relative importance of vibrations as compared to linear acceleration of droplets is the ratio between vibrational and translational kinetic energy. This ratio is given by 3a^2 ?/(?p?r_0 v?_transl^2 ) where vtransl is the translational velocity to which the droplet has been accelerated by the shock front. This ratio is negligible for a particular severe explosion scenario where information on vtransl was available in the literature. For other cases vibrations might be of some significance but detailed information about the specific scenarios is needed to obtain detailed results. More work is needed in order to understand the effect of viscosity and higher order vibrations. Furthermore a model for the excitation of droplet vibrations by shock waves is required for modelling. Finally there is a lack of experimental knowledge on droplet size distribution for water mist interacting with a shock wave.

Two types of electrical measurements have been investigated in order to perform diagnostics of the fire dynamics in the ISO 5660 cone calorimeter. The rationale of the study is to take advantage of the pilot ignition electrodes that are already in place and use these to collect additional information such as emission of pyrolysis gases and time to ignition. The first part of the project was a refinement of the method for measuring the so called ion current, which has already been investigated in a pilot study. It was found that thorough shielding and grounding gives an excellent signal to noise ratio. An expression for the correlation between measured current and conductivity was also developed and validated experimentally. The second part of the project consisted of measuring the breakdown voltage, that is the voltage when dielectric failure occurs. It was found that this method was more sensitive to the fire dynamics before ignition, such as pyrolysis, but that the response to ignition was more ambiguous for the breakdown voltage than for the ion current.

Two types of electrical measurements have been investigated in order to perform diagnostics of the fire dynamics in the ISO 5660 cone calorimeter. The rationale of the study is to take advantage of the pilot ignition electrodes that are already in place and use these to collect additional information such as emission of pyrolysis gases and time to ignition. The first part of the project was a refinement of the method for measuring the so called ion current, which has already been investigated in a pilot study. It was found that thorough shielding and grounding gives an excellent signal to noise ratio. An expression for the correlation between measured current and conductivity was also developed and validated experimentally. The second part of the project consisted of measuring the breakdown voltage, that is the voltage when dielectric failure occurs. It was found that this method was more sensitive to the fire dynamics before ignition, such as pyrolysis, but that the response to ignition was more ambiguous for the breakdown voltage than for the ion current.