[Sir_Humphrey]

If this is was a bomb , then where is the damage done to the building ?

[kiryandil]

Pressure cooker type nail bomb.

https://twitter.com/search?q=Manchester&src=tren&data_id=tweet%3A866788808490078208

[citizen]

Personal injury bomb, such as Boston Marathon pressure cooker bombs. Flying nuts & bolts, like that.

[Freee-dame]

If this is was a bomb , then where is the damage done to the building ?

I heard on the radio that it happened outside of security in the area where vendors were selling things. It happened just as everyone was leaving so people were densely packed together. accurate? who knows this early?

[Spktyr]

Nail bombs typically have relatively small explosive charges wrapped by as many nails, bolts, jagged metal and other intended shrapnel as possible. The method of wounding or killing isn’t the explosive’s blast effect but the clouds of high speed metal it propels. Typically damage to buildings is minimal.