Different topic:
With fragmentation and improvised hand grenades having lost their direct damage effects the question remains, what the crit values are (maybe refering to other blast weapons would be sufficient?).
Is there already news on the crit level for hand grenades? As per the table on p. 68 (PM), crit levels are +/-1 of the damage value of explosions. With the relative low level of hand grenade explosions in mind, but considering that the base damage is "0", I feel that a crit value of "1" would be within reasonable range compared to other explosions and reflecting actual lethality of hand grenades.
I must admit, I'm not too happy with the solution of reducing base damage to "0", because it means that the maximum damage achievable is "2" for hand grenades. That makes it impossible to harm or even critically injure characters eqquipped with heavy armor, unless an uncovered location is hit. Also, a person with any form of protection in the form of armor value need not fear critical hits from hand grenades, as no critical injuries could happen. Effectively, this means that hand grenades cannot "kill" characters, since fatal injuries are soley the product of critical injuries in T2K. That seems to be a gross misconception of the battle field impact hand grenades have.
Additionally, I don't get, why a hand grenade with its blast power of "C" should have so much less base damage than any ordinary type "C" explosion? Certainly a device especially constructed for the explosion and destruction of personell should not be inferior in effect to any regular type of explosion with the same basic power?
Finally, I would argue in favor of a blast power or other damage modifier in enclosed spaces, especially if they are roofed. Something like +1 damage for 3 or more walls and +1 for a roof, alternatively shifts upward in the blast column could be applied or a reduction of the crit value could be considered.
Note: The example for explosions on p. 68 (PM) uses a hand grenade for its calculations and should also be revised, reflecting new rules.