**Period of Structural Adequacy Under Fire**

The correct answer is option 'B' - Period of structural adequacy under fire.

**Explanation:**

During a fire, the structural elements of a building are subjected to high temperatures, which can cause them to weaken and eventually fail. The period of structural adequacy under fire refers to the time it takes for the structural elements to reach their limit state of inadequacy and become unable to perform their intended function.

This period is typically measured in minutes and is an important consideration in the design of fire-resistant structures. It helps determine the level of fire protection required for the structural elements and allows for the implementation of appropriate fire safety measures.

The period of structural adequacy under fire depends on various factors, including the type of structural material, the dimensions and configuration of the structural elements, and the fire load within the building. Different materials have different fire resistance properties, and therefore, the period of structural adequacy may vary.

Fire testing is conducted to determine the fire resistance of structural elements and systems. These tests involve subjecting the elements to controlled fire conditions and measuring their performance over time. The period of structural adequacy under fire is determined by observing the time it takes for the elements to reach their limit state of inadequacy, such as excessive deflection or failure.

It is important to note that the period of structural adequacy under fire is not the same as the fire warning period or the fire collapse time.

- The fire warning period refers to the time it takes for a fire to be detected and for occupants to be warned about the fire. It is typically measured in seconds or minutes and is crucial for timely evacuation and fire suppression efforts.
- The fire collapse time refers to the time it takes for a structural element or system to fail completely and collapse under the influence of fire. It is an important consideration for emergency responders and can affect rescue operations.

In conclusion, the time in minutes for a member to reach the limit state of structural inadequacy in a standard fire test is known as the period of structural adequacy under fire. It is an important parameter in the design and evaluation of fire-resistant structures, helping determine the level of fire protection required for the structural elements.