How quickly can the water in a boiler's gauge glass drop from half full to empty?

The timeframe in which the water in a boiler's gauge glass can drop from half full to empty is typically measured in minutes. This is due to the rapid changes in pressure and temperature that can occur within a boiler system. If there is a sudden loss of water due to a malfunction or issue, the gauge glass can reflect this change quite quickly because it provides a direct visual indication of the water level.

Conversely, while it might seem intuitive to think that it could take longer periods, such as hours or days, for such a significant drop to occur, real-world scenarios often demonstrate that the dynamics of water levels in pressurized systems can lead to swift changes. Therefore, the critical response time in monitoring boiler operations focuses heavily on the understanding that gauge glasses can reflect water level changes rapidly, justifying the minutes timeframe as the most accurate answer.