I deal with barrels all day long at work... remember even things that seem harmless may not be. Any kind of oil, including food grade soy, corn or other oils are flammable and in the right situation explosive!!! Other things to keep in mind is that things like corn syrup, malt extract, and other high sugar items that are transported in 55 gallon drums are flammable as well when exposed to the right ignition source.
The best bet would be to search out a barrel that has a clamp on lid. I personally have obtained several corn syrup barrels that have the lids held on with a clamp. These don't require cutting to get them open. You can then thoroughly wash the corn syrup away completely with some hot water and a bit of soap.
Take the time to find a drum that isn't going to hurt you!!! think about what was in it!!! if you wasn't the one who emptied the ingredients be suspect of what may have been in it!!!
One last idea... Years ago my grandfather had a barrel opener that he used in the gas station he owned. It was a giant version of a P-38 can opener that he had made. (P-38 can opener picture can be found here P-38
the handle was about 5 foot long and with a guy to hold the barrel and one to operate the can opener a barrel could be opened in a matter of minutes. Grandad, did not like the idea of wasting anything and would then be able to get every last drop of oil out of a barrel... and those who know me think I'm chintzy!