My thoughts are that say using the Dash 8 example above. The company will gain approval for 1:50 but normally operate with 2 CC on board for service delivery reasons. This gives the flexibility then, if a CC goes sick at short notice, or for a recovery flight they can operate with one CC.
Taking a wider view here, when travelling on a packed commuter train in any Australian capital city, who helps you evacuate from the train carriage in an emergency? No power to run the pneumatic doors, no power to run hydraulic doors, carriage on its side, possible fire. You are on your own. We all accept this as normal, rational and safe. (whatever safe is, no such thing as absolutely safe)
Travel on a serious size ferry on Sydney harbour, or down to Tasmania on the car ferry, or over to any one of a number of Qld Islands. Do the staff numbers look like anything like 1:36?
We get very precious about aviation safety, this has ended up with full body scanners, no nail clippers and pilots who cannot take a 200gm can of tuna to work with them. Is this really what we want or need? Don't interpret this as me saying we should disregard safety, of course we should aim for safe operations. We should also look around at what goes on elsewhere and pick the relevant parallels.
For my money the manning of each exit is important not whether there are crew at say 1L and 1R so long as one is at that pair. I cannot see major issues with 1:50 if that is how many aircraft were certified anyway. It is in the same category to me as the TO distance charts having 15% added for Australian conditions; we just had to be different. The US has plenty of hot/high airfields but they seemed to cope with manufacturers data.
I think most operators will use this as a get out of jail free card when it comes to CC sickness and shortages.
As a matter of historical interest can anyone give an example of a slides out evacuation carried out anywhere in Australia? New Zealand? How did it go?