Reading this made me sad:
Early detection [of a bomb] can backfire because of the grisly fact that human beings act as human shields. "There is a trade-off between crowd size and crowd blocking," says Prof. Kaplan. A large, dense crowd puts more people in harm’s way, but "the probability of being exposed to a bomb fragment declines exponentially with the size of the crowd." As a crowd flees, there are fewer people near the bomber to absorb the fragments (as when a soldier falls on a grenade) and more people, unshielded, farther away. Simple geometry shows that you can hit more people at a radius 20 feet from a bomber than you can five feet from him…The same effect occurs if people throw themselves to the ground That minimizes each person’s exposed area, but also at the expense of decreasing human shielding. For bombs with 500 or more fragments (in Israel, 1,000 is typical), "hit the deck" can raise rather than cut casualties.
That is from The Wall Street Journal, 8 July 2005, by Sharon Begley.