What would be a fair way to adjudicate the detonation of a grenade in an enclosed space, such as a stairwell?
I have used the rules for blowback in games such as Shadowrun before, but recently ran a scene in an A Time of War session where a soldier lobbed grenades after a fleeing group of PCs as they ran down several flights of stairs. Due to the circumstances of the scene, the detonation did not affect anyone, but what if it had?
If the grenade exploded in a narrow flight of stairs, what would happen to the force and shape of the blast? If the blast was defined as being 12 points of damage at the point of detonation, and decreasing 1 point per circular meter it expands outward from that point, what would be an appropriate modification for the blast if it occurred in a space 2m wide and 3m high, with flights of stairs spanning 4m of horizontal distance and dropping 4m within that span.
(I recognize that these figures may not actually represent a sane flight of stairs, please indicate more appropriate stair stats in your answer if you like. I present these here as these are the dimensions I used in the session. )
Also, it should be clarified that I am interested in all aspects of the explosion, including but not limited to increased damage, increased range where the blast can escape, secondary effects such as deafness, dust clouds, etc.