I served 26 years in the Army with 20 in the Explosive Ordnance Disposal field, my last tour in Iraq in 2010 I did post blast investigations/reconstructions. My partner I worked with in Iraq is in Kabul right now, I communicated with him yesterday. His initial thought from hearing the explosion was a VBIED. Apparently is was a suicide bomber strapped with about 50-100lbs of semtex or C-4. Yes a bomb that size could easily create that much damage and destruction in a very crowded area, especially if nails or ball bearings were added. The British were responsible for the Bomb Disposal school that taught the trade to the Afghani Army so yes there are tons of plastic explosives left behind.
Thanks for that info, just hard to believe you could get through a check point undetected, unless it was planned to get through undetected.
Yeah, I looked up the minimum safe distance for 100lb of C4 open on the ground: 1,500 feet. Concussion kill radius is almost 1,000 feet.