When must a triathlete have their helmet on?

• Fastened: the helmet must be "securely fastened" and fit properly at all times "when the athlete is in possession of the bike".
• Approved: by a national testing authority recognised by a federation affiliated with World Triathlon.
• Unaltered: it is prohibited to change any part of it, the chin strap included. Leaving any part off is prohibited too.
• Always when riding: in competition, course familiarisation and training sessions.
• Leaving the course: an athlete who takes the bike off the course may not unfasten the helmet until outside the course boundary and off the bike.
• Coming back: it must be fastened again before returning to the course or remounting.
• Numbers: race number stickers go on the front and both sides. No other stickers.
• Not on the run: athletes may "not run with a bike helmet on".
• In transition: the helmet may be placed on the bike beforehand, and at the end it goes in the bin.
• The penalty: a helmet infringement in transition is a time penalty. The amounts are in an appendix that was not read.

The glossary has the transition area, the bike course, the time penalty, the transition, the technical official and the penalty.

Tying the helmet to possession of the bike, and not to riding it, gives officials one clear thing to check at the rack and leaves no gap. The moments straight after mounting and shortly before dismounting, in a crowd, are when falls happen. It is among the commonest penalties in the sport, because athletes rush.