What makes watertube boilers generally safer than firetube boilers?

Watertube boilers are considered generally safer than firetube boilers primarily because of their design, which results in a smaller volume of water and steam contained within the system. In watertube boilers, water circulates in tubes that are heated externally, allowing for a more controlled and stable pressure environment. Should an issue arise, the smaller volume of water means there is less potential for an explosive failure compared to firetube boilers, where large amounts of hot water and steam are present. This greatly reduces the risks associated with pressure surges and overheating.

The other aspects related to safety, such as the ability to withstand pressure, materials used in construction, and cost-effectiveness, do play a role in the overall performance and reliability of the boilers. However, the fundamental design characteristic relating to the volume of water and steam is the primary reason for the enhanced safety profile of watertube boilers.