During normal operations, how should one react to a significant loss of Brake Pipe pressure?

When faced with a significant loss of Brake Pipe pressure during normal operations, initiating emergency brake procedures is the appropriate course of action because it directly addresses the critical safety concern posed by reduced braking capability. A significant loss in Brake Pipe pressure can compromise the train's ability to brake effectively, increasing the risk of an accident.

Emergency brake procedures are designed to bring the train to a safe stop as quickly as possible when faced with such an issue, prioritizing the safety of passengers and crew. This response aligns with established protocols for handling situations that could lead to an unsafe operating condition, ensuring that the train does not continue moving when it may not be able to stop in a controlled manner.

The other responses do not adequately address the immediacy and severity of the situation. Checking for leaks or attempting to assess the system during such a critical loss of pressure could delay necessary action and heighten risk. Similarly, continuing to move the train at reduced speed is not advisable, as any further loss of braking capability could lead to an even more dangerous situation.