Which pressure must safeties be lifted to if a steaming boiler suffers a ruptured tube?

In the event of a ruptured tube in a steaming boiler, it is crucial to ensure that the pressure in the system is reduced to a safe level to prevent further damage and ensure the safety of personnel. Lifting safeties to 0 psig indicates that the boiler pressure has been reduced to atmospheric pressure, eliminating the risk of high-pressure steam causing additional hazards or injuries.

When a boiler tube ruptures, it can lead to the release of steam and water under high pressure, which can be extremely dangerous. Bringing the pressure down to 0 psig essentially means venting the system to relieve all pressure, rendering the boiler safe to inspect and repair.

The other pressure levels mentioned do not account for the immediate safety needs after a significant failure like a ruptured tube. Continuing to maintain any pressure above atmospheric level after such an event could lead to further accidents or complications, which is why reducing the pressure to 0 psig is the established safety protocol in these situations.