This is a good question
For me the most important thing is a blunt tip . Put yourself in a rescue situation in the dark and maybe chuck some foul weather in too
Your driving along and the car infront of you swerves to miss a Deer , looses control and turns upside down into a water filled ditch
Before you know it your up to your waist in freezing cold water next to the upturned car and trying to get the occupent/s out . In that situation a glass breaker would be very nice but in a pinch the corner of a full size multi would have to do . No time to cover the window with tape here .Obviously you wouldn't break a window if it fully submerged under the water ( unless you have no choice ) . Next you may have to cut the seat belt if it won't come undone and this is where a blint tip comes in . Imagine poking a very sharp blade about in the wet and dark trying to get between the casualty and the seat belt , you may have to push hard aswell . I don't need to explain what could happen if you slip
Of course this is just one type of rescue but I think Vehicle rescue is probably one that most members could find themselves in .
But there are many other types of rescue and a glass breaker wouldn't be much good up a mountain of out in the sea . But a Blunt tip blade is IMO a must have .
On our lifeboat we used to have this huge Diving knife , I reckon you could have killed a wale with it . But as a rescue knife it was usless and has now been replace with a Spyderco Atlantic Salt left in the open position and stored in a Kydex sheath ( Thank you Mojofilter
) that is bolted to the centre console of the boat .In this case its yellow handle is very usefull as th bottom of the boat is orange with black cables and other equipment so it stands out very well .
So for me a Rescue knife must have a blunt tip blade , be serrated and easily opened and accessed .I think the blade should be at least 3 inchs.I also think it should be paired with a full size multitool . Not all rescues involve cutting clothing and equipment away from casualties. Things still break , jam and go wrong on rescues just as they do in normal life . My Swisstool has seen far more use on rescues then any other knife .
Dunc