I'll throw my 2cents in the hat...
IIRC during the Blue Peter dry pipe failure the engineer attempted to center the gear and was severely injured when it disintegrated and transmitted some of the energy and destruction back into the cab. I've seen a manual johnson bar take an engineer for a ride trying to hook it up a notch, If i had a power reverse gear and felt comfortable with the conditions I'd put it in the corner in hopes of choking it with back pressure, centering it would be just like hooking it up.
The order may be altered depending on convenience or where your hand are when it happens
Engineer
1. Open cylinder cocks
2. Apply breaks
3. start injector on full
4. Adjust reverse gear if safe and practical.
5. consider joining the birds.
Fireman if coal:
1. Start the injector
2. Dump the fire
3. Consider joining the birds
Fireman if Oil:
1. Pull the emergency fuel shutoff
2. Start injector
3. Red Bull, it gives you wings....
Not included to any order position. Pay attention to the other side of the cab. the fireman might be struggling to dump the fire, or the engineer with the injector. When a fecal distribution system of this size hits full RPM you will need to the demands of the situation. I'd go as far as to say if you do need to jump don't leave your fellow crew hanging.
you could argue whether to open or close the dampers or fire doors to help cool things off, if things are bad enough to jump I'm pretty sure that any benefits of damage to the boiler would be inconsequential to where things would be going.