What is the danger of low water levels in a steam boiler?

Low water levels in a steam boiler present a significant hazard, primarily because they can lead to overheating and subsequent tube failure. When the water level drops below the safe operating threshold, the boiler tubes become exposed to the intense heat generated during combustion without the protective cooling effect of the water.

This overheating can cause the metal tubes to expand excessively; if the temperature rises too high, the material integrity of the tubes can be compromised, leading to sagging, warping, or complete failure as they may weaken and eventually rupture. This failure not only poses a risk of catastrophic boiler failure, but can also result in dangerous situations such as explosions, steam releases, and significant damage to the surrounding area or equipment.

The other options, while valid concerns in their own right, do not encapsulate the primary danger presented by low water conditions. They relate to potential operational issues or secondary effects, but the central and immediate danger of compromising tube integrity and causing overheating is most critical and can have immediate safety implications.