Quote (kragujevac @ Apr 15 2013 02:54pm)
they can be concealed
Yea, they can, but at events like this, security is trained to look for random bags laying around. For an explosion of that scale, we're talking a hefty pipebomb that is probably closer to 70-80 pounds.
This is a 25 pound pipebomb (6 feet in length) and is about 1/4 the size of that explosion. Things like that, as I said, would be notice. Especially someone struggling to carry that backpack.
http://www.youtube.com/watch?v=tFoDHsCJwdEIf it was another type of explosive, it might have been smaller, but it wouldnt be significantly lighter in terms of weight.