Over recent years, there is considerable interest in the research of vehicle fires in car parking buildings. The acceptance towards performance-based design engineering approach around the world has led the use of engineering approaches to the assessment of fire safety in structures. In fire safety context of performance-based design, one of the fundamental components is design scenario. The aim of this thesis is to formulate an approach that is able to develop appropriate design fire scenarios for vehicle fires in car parking buildings using probabilistic assessment methods as part of a risk-based approach. This is achieved by creating a probabilistic model to investigate the risks associated with vehicle fires in car parking buildings, such that fire risk is equal to probability multiplied by consequence. The probability component depends on a number of factors which are the vehicle parking distribution probability, i.e. the probability of vehicles being distributed in a particular pattern throughout the building at a given time; the vehicle classification i.e. the composition of different vehicle types in a fleet; and the vehicle fire involvement, i.e. the likely number of vehicles involved in a fire. The consequence component is defined as the severity of the fire in terms of fire growth, energy released, and number of vehicles involved in burning. The thesis consists of three tasks; the first task is the collation of results for single passenger vehicle experiments and the application of probabilistic assessment model for vehicle fire scenarios in car parking buildings. In the first task, probability distributions for fire severity characteristics for a single passenger vehicle are introduced and a probabilistic quantitative fire risk analysis is performed. The second task enhances specific probabilistic assessment components based on the findings made in the first task. Two main focuses in this task are to introduce probability distributions of characteristics for the design fire curves for a single vehicle, and to develop an approach of predicting the time to ignition for subsequent vehicle given the first vehicle is already burnings as there is a need to assess the fire spreading between vehicles. The final task applies the enhanced components obtained from the second task into the probabilistic assessment model. As a result, a conclusion is drawn following the completed work in the final task. Example demonstrations of the application of the probabilistic model are also shown in the thesis. One is using probabilistic model to determine the fire load energy densities for risk-based design of car parking buildings. The other work is about the analysis of the probability of fire spread from a vehicle to another vehicle in car parks.