This report describes an experimental study that provides research information and data to assist with understanding the mechanisms for successful water mist fire protection systems in offices. Water mist systems are increasingly being considered and used in the UK for the fire protection of buildings, including commercial premises such as hotels, offices and retail units. They can provide property and asset protection by limiting the extent of damage associated with a fire and thereby limiting unnecessary wastage of resources, time, salvage and re-instatement operations. However, the acceptability of water mist systems is often unproven, the limits of their effectiveness are largely unknown and appropriate acceptance criteria are not well established. Successful water mist performance can only be achieved by carefully engineered designs to meet particular applications. The objectives of this study were to:• characterise the mechanisms and factors that govern the effectiveness of water mist fire protection systems • define a fire test protocol for evaluating water mist fire protection systems for commercial office applications. • address some of the identified gaps in knowledge with respect to water mist systems. It is only with this knowledge and understanding that fixed water mist suppression systems can be assessed and confidence given that they will be effective in protecting property and life.