Update this morning from ESA’s Mike Steinkopf at ATV-CC.
The ATV-ISS pressure equalization has been performed and crew just reported that the ATV hatch is open!
Crew will now carry out the ‘Initial Ingress’ procedure, which consist out of crew taking air samples of the ATV air for later air quality analysis on ground.
Then Crew will install the Scrubber Device (an electrical powered Airfiltering Device) in the Aft Cone (opposite to the ATV hatch) to further clean the ATV internal air volume for a duration of about 4hrs:40mins. In addition, a so-called Scrubber Curtain will be installed close to the ATV hatch inside ATV.
For the duration of the air scrubbing, the Hatch will be closed again (but not latched). After the scrubbing duration the Scrubber will be switched off. The ‘Final Ingress’ process (scrubber removal, etc.), full hatch opening and access to the ATV payload is scheduled for later today; then ATV is fully accessible and the Cargo Transfer Operation can start.
— Mike Steinkopf