What condition exists at 60% tank level in a mercury system?

In a mercury system, when the tank reaches a 60% level, the typical condition is that the duty pump is running. This indicates that the system is actively managing the liquid level to maintain optimal operation. The duty pump's role is to ensure that the liquid is being circulated or processed as needed, which is crucial for reliability and efficiency.

At this level of fill, it's anticipated that the system is still within its ideal operating range, and the duty pump is engaged to maintain the liquid's movement or to prepare for any changes in demand. This situation is managed to prevent any potential overflow or underflow in the system, which could compromise safety or operational effectiveness.

The other options suggest conditions that typically occur at different tank levels or system statuses. For instance, a standby pump might be activated during a low pressure or demand scenario, while an alarm would trigger at a higher level potentially indicating a risk situation. Understanding the operational logic of pump management in relation to tank levels helps in maintaining system safety and efficiency.