Final answer:
To confirm Nonel tubes' initiation, trained professionals observe the initiation sequence, potentially using test equipment, while adhering to rigorous safety protocols due to the explosive materials involved.
Step-by-step explanation:
To check that Nonel tubes have been initiated, one would typically use a method to observe the initiation sequence and confirm the detonation. While the question does not provide enough context to describe a specific procedure for Nonel tubes, commonly used in mining and blasting operations, the general idea is to ensure that the tube has been properly activated and is transmitting the shock wave or detonation signal as intended. In common practice, this might involve an observation of a connected detonator's function or the use of test equipment designed to detect the initiation. However, any such checking procedure must be carried out by trained professionals who follow strict safety protocols inherent to the explosive nature of the materials involved.