Final answer:
If a diver's comms are down, they can use pulses or bangs on a tank or structure to signal topside as part of established safety protocols.
Step-by-step explanation:
If you are a diver and your communication systems fail, it would be important to have a pre-determined protocol for such situations. One way to check if topside can still hear you without the comms is to use a standard series of pulses or bangs on the side of the tank or structure to create noise that can be heard through the water. This kind of acoustic signaling can be established before the dive as part of the safety protocols. If the topside crew recognizes these signals, they might respond with a similar method, such as a series of bangs on the hull or another structure that can be heard underwater, confirming that the communication has been received.