86. One boiler of a two-boiler plant has ruptured a tube, and the water cannot be maintained in sight in the gauge glass. After securing the fires, your next action should be to __________.

After securing the fires in a boiler with a ruptured tube and a low water level, the immediate priority is to stop adding water to the damaged boiler by securing the feedwater supply. This prevents further damage and hazards associated with water and steam escaping through the rupture, such as flooding the furnace and increasing the risk of water carryover.