What is the most critical rule for the safe operation of steam boilers?

Keeping water at the proper level in a steam boiler is essential for safe operation. This rule is vital because the water level directly affects the boiler's ability to generate steam safely. If the water level drops too low, it can lead to overheating of the boiler's components, which may cause severe damage, including potential explosion hazards. Proper water levels ensure effective heat transfer and prevent the boiler from running dry, where the metal can become damaged due to excessive temperatures.

While regular maintenance, monitoring fuel levels, and inspecting for leaks are also important practices for safe boiler operation, they do not address the immediate threat that low water levels pose to the overall safety and functionality of the system. Maintaining the correct water level is the first line of defense against a variety of operational problems, making it the most critical rule for safe steam boiler operation.