NFSI Firefighting Knowledge 4

Question 1

In a building fire, which floor presents the greatest collapse risk for firefighters conducting interior operations?

Accepted Answer

The floor immediately above the fire, due to heat weakening the structural assembly

Answer

The floor directly above the fire is most vulnerable because heat weakens structural members from below while the floor continues to bear live loads.

Question 2

What is the function of a pressure relief valve on a fire pump?

Accepted Answer

To prevent excessive pressure from damaging hose lines when flow is suddenly reduced

Answer

The pressure relief valve opens to bypass water and reduce discharge pressure when a nozzle is shut down suddenly, preventing hose damage or injury.

Question 3

What hazard is specifically associated with a trench or lean-to roof collapse?

Accepted Answer

Secondary collapse from unstable debris on top of the primary collapse

Answer

In a lean-to or trench collapse, debris on top of or leaning against the primary collapse is highly unstable and can cause a secondary collapse on rescuers.

Question 4

Which chemical property determines whether a flammable vapor will rise or sink in air?

Accepted Answer

Vapor density

Answer

Vapor density compares a gas's weight to air (air = 1); vapors with a vapor density greater than 1 sink and accumulate in low areas, while those less than 1 rise.

Question 5

What is the correct nozzle technique called when a firefighter sweeps water across the ceiling to cool hot gases before advancing?

Accepted Answer

Transitional attack (gas cooling)

Answer

Transitional attack, or gas cooling, uses short bursts of a fog or straight stream aimed at the ceiling to cool superheated gases and reduce flashover risk before advancing.

NFSI - National Firefighter Selection Inventory Practice Test

NFSI - National Firefighter Selection Inventory Practice Test

NFSI Firefighting Knowledge 4