What is the main purpose of test method B in the expansion and drainage test?

The main purpose of test method B in the expansion and drainage test is to obtain a sample that is representative of foam as it would function under actual fire conditions. This method simulates the scenario wherein foam is deployed in a real-world emergency, allowing for the assessment of how the foam will behave when subjected to factors such as drainage and expansion in a typical fire suppression situation. By focusing on this aspect, the test ensures that the foam's performance can be accurately evaluated based on conditions it will face when deployed, which is critical for determining the effectiveness of the foam in extinguishing fires. This means the results from test method B can be relied upon for practical application in fire-fighting scenarios.

Other options, while potentially related to foam characteristics, do not directly align with the specific intent of test method B. For instance, measuring viscosity is important in foam formulation but is not the focal point of this test. Similarly, evaluating foam's effectiveness on various surfaces and determining its environmental impact address different aspects of foam performance but are not the primary purpose of the expansion and drainage test.