The drawing you posted is representative of the three orbiters equipped with an *external* airlock and ODS for docking with ISS. Just aft of the docking assembly you will note a short tunnel section with truss around it. That's the EVA hatch for that particular payload bay configuration.The photo you posted shows the docking assembly, not an EVA hatch.

When Spacelab and Spacehabs are carried by orbiters with internal airlocks (i.e. Columbia) a tunnel adapter assembly about 90" long is added right outside the bulkhead of the crew compartment. That module has an exterior hatch right on top of it (with no vertical displacement to speak of) and an interior hatch at the aft end. The photo in the press kit show shows the tunnel section that mates to the module I just described.

shows the TAA installed in Columbia for a Spacelab mission, which used the same tunnel config as a SpaceHab mission.

and

show the completed assembly. The disc-shaped thermal cover shrouds the "C" hatch that an EVA crewman would use.

No orbiter has ever been flown without the provision for emergency spacewalks. Two EMUs are stowed in the airlock on every flight. ON STS-107, Dave Brown was one of two designated EVA crewmen. I don't know who the other one was.

-Kim-