312.12. Duties of the standby diver: The standby diver must
(1) remain on the surface and dive only in case of emergency to help a diver underwater;
(2) ensure that the required diving and communication equipment is ready for use in the environmental conditions surrounding the diver underwater; and
(3) be ready to dive in the environmental conditions surrounding the diver underwater within not more than
(a) 5 minutes for scuba diving; or
(b) 7 minutes for surface-supply diving.
In addition, the standby diver may not assist more than one diver at a time, except if the distance separating the standby diver from the divers’ entry points does not exceed 30 m.
A scuba diver may not act as a standby diver for a surface-supplied diver.