If a tank malfunctions, the diver can use the tank of a companion (tanks have two nozzles), and then they can slowly rise to the surface together.
拿「共生」為例：當一個潛水者在水深卅公尺處，空氣筒用罄或掉了時，同伴須將自己的空氣筒分對方使用，一人吸一口，一起慢慢游回水面。