Boeing engine fire on ground and evacuation
In the event of an engine fire on the ground, Boeing procedures call for using one fire extinguisher bottle, as this is likely will be more effective than discharging the 2 bottles (though there may be other reasons I'm not aware of). However, the last step in the evacuation checklist states, 'if an engine or APU fire is observed or indicated: rotate the related fire switch to the stop and hold for 1 second.' I interpret this as meaning that if the engine fire is still burning when pax are evacuating, I should discharge the second bottle. But what's the purpose of this step?