When must a steam boiler be equipped with two low water fuel cut-off devices?

A steam boiler must be equipped with two low water fuel cut-off devices when it is not continuously attended to ensure safety and prevent hazardous situations. The primary function of low water fuel cut-off devices is to detect the water level in the boiler. If the water level falls below a certain point, these devices will automatically shut off the fuel supply to the boiler, preventing it from running dry, which could lead to boiler damage or an explosion.

In situations where a boiler is not continuously attended, there is an increased risk of low water conditions going unnoticed. The second low water fuel cut-off device acts as a redundancy to the first, providing an added layer of safety. This requirement is particularly crucial in facilities that may leave boilers unattended for extended periods, as it helps to safeguard against potential accidents caused by human error or unforeseen circumstances.

This is in contrast to continuously attended boilers, where operators are present to monitor the water levels and operations, thereby reducing the need for such stringent safety measures.