What issue can arise from soot build-up on boiler tubes?

Soot build-up on boiler tubes can create a significant safety hazard, pertinent to the operation of the boiler. When soot accumulates, it acts as an insulating layer that prevents proper heat transfer from the flue gases to the boiler water. This lack of effective heat exchange can lead to overheating of the boiler tubes. Additionally, high temperatures, combined with the presence of flammable gases, can increase the risk of a furnace explosion if the accumulated soot ignites or if the combustion process is disrupted.

While the other options may also arise from soot build-up — reduced energy efficiency, increased fuel consumption, and potential corrosion — the immediate and most critical risk associated with heavy soot accumulation is the danger of an explosion due to overheating and flammable conditions in the furnace. Therefore, understanding the implications of soot build-up in the context of boiler safety is vital for effective power engineering practices, highlighting the importance of routine cleaning and maintenance.