I would think
one is the answer. I give you a USA FM ref. again tables 19 and 21 are your focus. Note safety distances for accompanying infantry in combat at 50M and for training at 100M. Browsing the web and going back to the earliest and therefore minimum coverage we're looking at about 30M to ~75 DEPENDENT on grenade type used. Most modern IR/LASER disruption types are ~50M+ as the tables above will indicate as they would release solid and chemical materials that might injure supporting troops again as noted above.
http://www.globalsecurity.org/milita...3-50/appc2.HTM
Regards,
Pat