The buffets have their own "steam tables" and no sterno is used. I have never seen sterno used and it probably isn't because there are no open flames on a cruise ship. All stoves, ovens and heating units are electric. No gas appliances on the ship.
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Upcoming Cruise(s) Carnival Liberty: May 31, 2014. The Anniversary Getaway.
"There is a great difference between being well traveled and just having been to many places." ~Me