The emergency channel was a block of communications channels reserved by Starfleet for emergency use. Starfleet personnel could use this channel to transmit a plea for help or a status update after a ship or station was disabled. An emergency channel had four digits.
In 2286, the Whale Probe disabled two starships. One of these ships, the U.S.S. Yorktown, sent a message on emergency channel 0130 to Starfleet Command. Captain Joel Randolph informed Command that his ship had lost all power. He hoped that his systems engineers could restore some power to his ship through a makeshift solar sail.
Then, the Spacedock sent a message on this channel after the Whale Probe had disabled the space station. In their message, station controllers informed Starfleet that the station had lost internal power. (Star Trek IV: The Voyage Home)