Which of the following is a crucial step before conducting maintenance on emergency equipment?

Before conducting maintenance on emergency equipment, one of the most critical steps is disconnecting the power supply. This action ensures the safety of maintenance personnel by eliminating the risk of electrical shock or accidental activation of the equipment while maintenance work is being performed.

When emergency equipment is powered, there is a possibility of it being inadvertently triggered, which could lead to dangerous situations. For instance, if maintenance is being performed on emergency lighting systems or automated emergency response equipment, failing to disconnect the power could result in these systems activating unexpectedly.

The other options, while important in their own right, do not provide the same level of immediate safety. Verifying the previous maintenance log is helpful for understanding the equipment's service history, testing all emergency signals is crucial for ensuring the equipment is operational, and reviewing emergency procedures is fundamental for proper response in emergencies. However, none of these steps address the immediate danger posed by electrical power when performing maintenance tasks. Thus, disconnecting the power supply stands out as the essential step before maintenance can safely commence.