PHILADELPHIA — A package bomb exploded in a downtown apartment early Tuesday after a man who apparently thought the manila envelope contained an inhaler opened it, police said. The victim was hospitalized with hand and chest injuries.

Agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were working with U.S. Postal Inspectors and the city bomb squad on the cause of the blast that injured a man at about 4 a.m.

CBS Philadelphia identified the man as 60-year-old Jim Alden.

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The man received the package Monday evening and opened it early Tuesday, apparently believing it contained an inhaler or other type of medicine, police said.

The package was “target specific,” Philadelphia Police Commissioner Richard Ross said. It wasn’t immediately clear if police know or suspect who sent the package, or why.

According to CBS Philadelphia, a box with a bar code was placed on the steps in front of the building.

Authorities say the package had a power source and loop switch. When it detonated there was a smell of sulfur in the apartment.

The victim was taken to Thomas Jefferson University Hospital and was in stable condition.

“As far as I know, there were no threats prior to this and no threats since,” Police Chief Inspector Scott Small said.

Police say they are looking at every possible explanation for the explosion, including the possibility of this being a hate crime. Officials tell CBS News they do not believe this is related to terrorism.

The man opened the package near the stove in the kitchen of the apartment he shares with a roommate, leading police to initially believe the blast may have been an accidental explosion caused by an inhaler getting too close to heat.

The damage from the blast was confined to the kitchen and included broken glass, Small said.

Aly King and Brian Muldoon live two doors down from the townhouse where the blast happened and said they didn’t hear any explosion, but their dog woke up around 3:45 a.m.

King said she let her puppy out in the backyard and that is when she heard firefighters in the alley, shuffling garbage cans, and saw emergency vehicles filling the street. They said they had never met the victim.

“It’s kind of a peculiar time of day to open a package, at 4 a.m.,” Muldoon said.

Ten residents were evacuated from nearby apartments, but were allowed to return after the bomb squad cleared other packages.

The victim’s 36-year-old roommate told police that the man often receives medical inhalers in the mail.