What defines the function of a hand pump in fire fighting?

The function of a hand pump in firefighting is defined by its manual operation, which aligns with the characteristics of option B. Hand pumps are designed to be operated directly by firefighters, allowing for immediate responsiveness in emergency situations. This type of pump is typically used when a quick, portable, and reliable means of getting water to suppress a fire is necessary, especially in areas where a larger pump may not be accessible or practical.

The manual operation allows firefighters to have direct control and flexibility over water flow and pressure, which can be crucial in dynamic firefighting scenarios. This hands-on approach is inherent to the nature of hand pumps, allowing teams to efficiently coordinate their efforts without relying on powered machinery.

In contrast, other options describe mechanisms that do not fit the hand pump's operational design. A gasoline engine would characterize motorized pumps, not hand-operated ones. An automatic pump would imply no human intervention, which directly contradicts the manual nature of hand pumps. Lastly, while hydraulic pressure is important in many firefighting operations, hand pumps do not rely solely on hydraulic pressure; rather, they are based on the physical effort exerted by the operator to create the necessary pressure to move water.