Read up here (Ironman):
http://www.ironman.com/...s.aspx#axzz4FXheDaUi

"Section 2.02 OUTSIDE ASSISTANCE
(a) Assistance provided by Race Referees or Race Officials is allowed but such assistance is limited to: providing drinks, nutrition, mechanical and medical assistance, and other necessary assistance (as may be approved by the Event Director or Head Referee).
Athletes competing in the same Race may assist each other with incidental items such as, but not restricted to: nutrition and drinks after an aid station and pumps, tires, inner tubes, and puncture repair kits; and (b) Athletes may not provide any item of equipment to an athlete competing in the same Race if it results in the donor athlete being unable to continue with his/her own Race. Such equipment includes but is not restricted to: shoes, complete bicycle, frame, wheels, or helmet. The penalty for this will be disqualification of both athletes."

And here (USAT and ITU):
http://triathlon.competitor.com/...low-competitor_93696