A B777 Captain reports he was unable to open the Pilot's Bunk Room door from inside the bunk area during a recent flight; essentially trapping him in the compartment. The inside door knob is polished metal; very slippery and offers virtually 'no grip'. The Bunk door was forcefully opened by a Flight Attendant. The reporter indicated that a similar event had happened previously.

Narrative

The B-777 Pilot bunk room aircraft; including this one; have an easily opened lever type handle on the outside of the door. The inside though is a round metal doorknob. These are often difficult to turn; particularly from the top bunk; or if one has very dry hands. On this flight I was unable to open the door from the inside; essentially trapping me in the bunk room. One Flight Attendant tried from the outside; without success; and another with more strength eventually was able to open the door. It; of course; is much easier to get leverage on this knob from the outside; due to the design. Though the humor of the event was not lost on my First Officers in the Cockpit; nor on I; it was of course quite serious. I have seen this happen before.A few months ago we were dispatched with a door locked closed; because Maintenance couldn't open it. I watched them struggle with it; and at the time; was oh so glad I wasn't inside. This design is in serious need of a re-design or modification. My suggestions: 1- Replace the inside knob with the same knob as on the outside. The current inside knob is polished metal and is very slippery with dry hands and offers virtually no grip. 2- Find a backup way to release the door pin from its floor catch; and make that available on the inside of the door. This must be accessible from the top bunk also; as it's nearly impossible for one to move from the top bunk to the lower bunk while the door is closed. My belief is that another Pilot could easily find himself locked-in for landing. Not at all safe. Of course we sent a Maintenance Report; and I personally showed the Mechanic in ZZZ the issue.