An apparatus (12) provides inflation fluid for inflating an inflatable vehicle occupant protection device (14). The apparatus (12) includes a primary housing (20), a primary inflation fluid source (100), a secondary housing (70), and a secondary inflation fluid source (200). The primary housing (20) is constructed from sheet metal by stamping. The primary inflation fluid source (100) is located in the primary housing (20). The primary inflation fluid source (100) is actuatable to effect a primary flow of inflation fluid out of the primary housing (20) to inflate the inflatable device (14). The secondary housing (70) is constructed from sheet metal by stamping. The secondary housing (70) is disposed within the primary housing (20). The secondary inflation fluid source (200) is located in the secondary housing. The secondary inflation fluid source (200) is actuatable to affect a secondary flow of inflation fluid to supplement the primary flow of inflation fluid. The secondary housing (70) has a first portion (7
