Stair access that has a three-hour fire door or hatch and a smoke-proof and airtight seal, or two sets of fire doors for radiant heat protection. 

A special roll cage that is designed to stop debris from blocking the exits

A fire bunker must be made out of appropriate materials. Some options:

•  Concrete: Reinforced concrete set into the ground deep enough so as to not be compromised (explode) from intense fire
• Wood: Built underground similar to a basement. Very thick timbers that char rather than burn rapidly, buying you time while the fire front passes
• Prefabricated: Specialized concrete reinforced with steel. Often modular in design and sometimes available as kits.  Completely buried or partially exposed.