Which of the following is a common cause of boiler explosions?

The common cause of boiler explosions is the combination of low water level and excessive pressure. When the water level in a boiler falls below the minimum required level, the boiler can overheat. This overheating can cause the metal components to weaken and eventually fail. Excessive pressure can arise if the safety valves do not function properly or if there is a failure in the control systems managing pressure.

In this scenario, the risk escalates significantly because inadequate water can lead to the creation of steam pockets that can suddenly expand as pressure builds, resulting in an explosive release of energy. Ensuring proper water levels and monitoring pressure are critical safety measures in steam operations.

The other options do not directly contribute to this explosive risk in the same manner. Excess air flow and improper ventilation can affect combustion efficiency and air quality but are not primary causes of boiler explosions. Regular maintenance is essential for safe boiler operation and helps prevent issues that could lead to an explosion, but it is not a cause of explosions itself.