When is it required for a boiler to have two safety valves?

A boiler is required to have two safety valves when it has more than 47 m² of heating surface. This requirement is in place to ensure safety and redundancy in the pressure relief system of the boiler. Safety valves are critical components that prevent unsafe pressure buildup within the boiler, which could lead to catastrophic failures.

The decision to mandate multiple safety valves is based on the size and capacity of the boiler. As the heating surface area increases, the potential energy stored in the steam also increases. In cases where a single safety valve might fail or become obstructed, having a second safety valve provides a crucial backup to ensure the boiler can still release excess pressure effectively.

The other criteria listed in the options relate to specific design and operational parameters but do not apply universally across all boiler types. The heating surface area specifically is a standard measurement used in codes and regulations to determine safety valve requirements. This ensures that as boilers scale in size and capacity, their safety measures are equally robust.