What are the levels of Vault?

The common treasury doors are graded, and the violent destruction time and fire resistance limit of each level are different, and they are also exquisite in terms of steel materials and locks. Different levels of vault doors are equipped with different locks and steel plates of different thicknesses.
There are four levels of Vault, which are M, A, B, and C. The M level is the lowest level, the C level is the highest level, and how are the treasury doors defined at each level? Their anti-violence destruction time and What is the fire endurance limit? What locks are used?
The M-class treasury door requires at least one set of special locks and a mechanical code lock to resist violent damage for 15 minutes and a fire endurance of 1.5 hours.
Class A vault doors require at least 2 mechanical code locks to resist violent damage for 30 minutes and a fire resistance limit of 2 hours.
Class B vault doors require at least 2 mechanical code locks and a set of time locks to resist violent damage for 60 minutes and a fire resistance limit of 4 hours.
Class C vault doors require at least 2 mechanical code locks and a set of time locks to resist violent damage for 120 minutes and a fire resistance limit of 6 hours.

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