Having been on many flights, sitting next to pax who can barely get up from a seat without assistance, I've often wondered who is responsible for these pax in the event of such an emergency.
One flight, from LHR to US, the guy next to me could barely use utensils to eat and used his diapers to relieve his bodily functions. (I know this because of odor) and yet he traveled alone. Sitting in an aisle seat, he would have been extremely difficult to crawl over, had there been an emergency evacuation, as he was a plump man.
Kids in car seats, senior citizens and the infirmed, will all become difficult in such evacuations and can impede those who are right next to them. Sadly, I suspect some of the fatalities will be the result of the above.