The Service Type should be a Dropdown Content Control with a title of "Service Type"
Your document should be saved as a docm so it can contain a macro
Bookmark the text that needs to hide/show with the name "Safety"
In the ThisDocument module in the document, copy in this macro
Code:
Private Sub Document_ContentControlOnExit(ByVal aCC As ContentControl, Cancel As Boolean)
If aCC.Title = "Service Type" Then
ActiveDocument.Bookmarks("Safety").Range.Font.Hidden = Not aCC.Range.Text = "Safety"
End If
End Sub