What type of equipment is primarily used to apply water in high-pressure situations?

The master stream device is specifically designed to deliver water at high pressures, which is essential for effective fire suppression in more significant or severe fire situations. These devices allow firefighters to project large volumes of water over a considerable distance, making them suitable for tackling fires that are beyond the reach of standard handlines. Master stream devices can be mounted on aerial apparatus or used on the ground, usually operated from fire engines or trucks, allowing for a more controlled and forceful application of water.

In contrast, handlines are typically used for smaller fires and are more manageable for individual firefighters rather than high-pressure challenges. Fire extinguishers, while useful in certain scenarios, are not designed for high-volume or high-pressure application and are limited in their capacity and range. A pumper truck is essential for supplying water and pressurizing lines but does not directly apply water itself; rather, it serves as part of the overall firefighting strategy to deliver water. Therefore, the master stream device stands out as the most suitable option for high-pressure water application in firefighting.