Why should water never be added to a boiler if there is no water visible in the gauge glass?

When there is no water visible in the gauge glass, adding water to the boiler can indeed lead to a potentially dangerous situation, specifically a boiler explosion. This occurs because the boiler may already be at high temperatures due to steam generation, and introducing cold water suddenly can create a thermal shock. The rapid change in temperature can cause the water to instantly convert to steam, leading to an explosive increase in pressure. This condition, known as a "water hammer" or "steam explosion," is extremely dangerous and can result in catastrophic failure of the boiler or serious injury.

Understanding the risks involved with adding water without proper monitoring of the water level emphasizes the importance of clear visibility in the gauge glass and the necessity of maintaining proper water levels before any adjustments are made. This highlights the need for rigorous safety protocols and the implementation of proper techniques in boiler operations.