Before entering a boiler for internal inspection, what must be done with the blow off, the main steam stop valve, and feed-water valves?

Before entering a boiler for internal inspection, it is essential to lock the blow off, the main steam stop valve, and the feed-water valves in the closed position. This crucial safety measure ensures that all sources of steam, water, and pressure are securely contained, preventing any accidental release that could lead to serious injuries or fatalities.

Locking these valves in the closed position ensures that no steam can escape, no water can enter, and that there is no risk of any unforeseen pressure build-up in the boiler while personnel are inside conducting inspections. This practice is part of a broader safety protocol known as lockout/tagout (LOTO), aimed at controlling hazardous energy. It helps establish a safe working environment, allowing inspectors to perform their duties without the dangers associated with active boiler operations.

The other choices would not provide the necessary safety measures. Leaving the valves open could result in the inadvertent release of steam or water during inspection, while tagging them in the open position or removing them entirely could create even greater hazards by failing to control the boiler's internal environment. Therefore, locking them in the closed position is the best practice to protect those entering the boiler.