Final answer:
In hydraulic ventilation, set the fog nozzle on a fog pattern to clear smoke and heat from a structure using the entrainment principle where increased fluid speed creates low pressure.
Step-by-step explanation:
When performing hydraulic ventilation, it is recommended to set the fog nozzle on a fog pattern. This technique is used by firefighters to clear smoke and heat out of a structure after a fire has been extinguished. By setting the nozzle to create a wide-angle fog pattern, a firefighter can take advantage of the air movement created by the low pressure of the fog to help draw out the interior contents, such as smoke, towards the opening with the nozzle. This practice is closely related to the principle of entrainment, where the speed of a fluid is increased to create low pressure, entraining one fluid into another, similar to the examples provided in the reference images (c).