Hardcore Ironman works in the exact same way as a standard Ironman account, simply with the added challenge of only one life. Your one life will only be claimed by a dangerous death. Safe deaths, such as those in many minigames, will not cause you to lose your Hardcore status.
There are no second chances as a Hardcore Ironman. If you fall into the clutches of death, you will be stripped of your Hardcore status and your stats will be frozen on the Hardcore Ironman hiscores.
Following a death, you can continue your adventure as a standard Ironman.
Following next week's game update on Thursday November 10th, you'll be able to talk to Juan as you exit Tutorial Island to start your journey as a Hardcore Ironman.
Prepare to take on the greatest challenge Old School RuneScape has to offer!