53 Pa. Stat. § 16599
The mayor of the city of Philadelphia is hereby authorized, whenever in his judgment the occasion demands it, to issue subpoena, in the name of the state of Pennsylvania, to any person or persons, requiring them to attend before him, or the fire marshal, at such time and place as may be named in said subpoena, then and there to testify, under oath or affirmation, which the fire marshal, in the absence of the mayor, is hereby empowered to administer, as to the origin of any fire occurring within the bounds of the consolidated city of Philadelphia, and also as to any facts or circumstances that may be deemed important to secure the detection and conviction of any party or parties guilty of the offences of arson or attempted arson.
53 P.S. § 16599