Sarin is extremely deadly organophosphate nerve gas that causes paralysis of all muscles including the muscles used for breathing...you die of respiratory failure within a few minutes without the antidote (IM Atropine SO4). One of these shells set off inside a basketball game, hockey game, or subway could conceiveably kill hundreds of people.
Point well made, but probably in a scenario like that the numbers would be higher. For one thing, panic would kill many people too as they watched people convulsing on the ground and dying. But the good part is that these are old, not brand new, rounds. So it's not like it's really, really bad WMD.