The following regulations apply whenever someone is wholly or partially submerged and is using a face mask and snorkel or underwater breathing apparatus. A divers-down warning device may be a divers-down flag, buoy, or other similar warning device. These devices are designed for, and used by, divers and dive vessels as a way to notify nearby boaters that divers are in the water in the immediate area. The device must be displayed prominently when in use. The divers-down warning device must meet the following requirements.