At Tufts Medical Center, surgeons fixed the smaller of the two bones in her lower left leg that was apparently shattered by shrapnel from the blast.

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At a U.N. compound next door to the scene of the attack, anxious U.N. employees hunkered down indoors after shrapnel from the initial blast sprinkled the gardens.

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Feinberg's warning to lower expectations wasn't lost on Dan Loring, whose daughter, Brittany, was so badly hurt by shrapnel from the first blast that she was in the hospital for 11 days.

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Secondary blast injuries are caused by flying objects such as shrapnel.

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George Velmahos, chief of trauma surgery at Massachusetts General Hospital, where many of the wounded were taken, said some had blast wounds "as well as small metallic fragments that entered their body - pellets, shrapnel, nails".

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