Philadelphia police officers were on patrol at 9:30 p.m. Tuesday when they heard a blast coming from the area of G and Allegheny streets in the city's Kensington section.
They found the 12-year-old boy injured and running toward his home on Custer Street, Officers took him and his mother in a patrol car to St. Christopher's Hospital for Children.
Police said the boy was with a friend when he lit some type of explosive device and attempted to hold it as long as possible before letting go, with the device ultimately exploding in his hand.
Philadelphia Police Chief Inspector Scott Small said, "The 12-year-old boy suffered severe injuries to his left hand. His left fingers and left hand are seriously injured. Right now, he is in critical condition, however, it's nothing life-threatening."
According to officials, the boy was immediately taken into surgery at St. Christopher's where surgeons removed the remaining part of his left hand. He is reportedly in critical but stable condition.
The Bomb Squad came to the scene to determine what exactly exploded in the boy's hand. It's not yet known exactly what type of device it was - or if it was a firework, if it was within legal limits.
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"We're not really certain what type of explosive device he was handling. It appears that with the injuries to his hand and it was such a loud explosion, they believe possibly something like an M-80 or something the size of a quarter stick of dynamite in that area, we're not certain," said Small.
M-80 fireworks are illegal under federal guidelines because they have more explosive power than what's allowed.
Police said real-time crime cameras captured the entire incident.