Mayor-elect Jim Kenney is conducting a national search for candidates to head three major departments - prisons, fire, and human services.

Prisons Commissioner Lou Giorla is retiring after nearly 34 years on the job and nearly eight as commissioner. Fire Commissioner Derrick Sawyer, a 30-year veteran, has been at the helm 18 months and will stay as acting commissioner until a successor is named.

Vanessa Garrett Harley has led the Department of Human Services (DHS) since 2014, and previously was deputy commissioner of its Children and Youth Division.

Internal candidates will also be considered for the various posts, Kenney spokeswoman Lauren Hitt said. "We're not looking outside the city because of inadequacies in the existing department," she said in an email. "We think it's important to consider external candidates as well as internal ones because of the varying perspectives they bring."

Until now, Kenney, who takes office Jan. 4, has filled top posts in his administration from within the city. The national search has been underway for several weeks, and decisions will come early next year, a news release said.

In the meantime, Sawyer and other top brass have agreed to serve as acting commissioners. Mike Resnick, Mayor Nutter's director of public safety, will be acting prisons commissioner.

Kenney, a firefighter's son, has said the Fire Department needs more resources, and has criticized some decisions predating Sawyer's tenure, such as a move to rotate firefighters among firehouses.

At DHS, Jessica Shapiro, who is Harley's chief of staff and has served at both DHS and the city law department, will become acting commissioner.

Kenney said last month he wanted an independent review of DHS, an often-criticized agency that has been implementing 10 years of reforms.