I won't claim to have any idea what I am doing, but, I keep a 45 gallon drum, with a lid, nearly full of used diesel engine oil. I was told that this quench contains more carbon available for absorption. I have never had a problem with flaming. The idea is to completely submerge the part quickly, then rotate it in a circle without turning the part, giving it an equal exposure to the oil moving around it.
The only flaming is at the contact point while the part is being submerged. The flame goes out once the part is away from the air. The part will boil the oil for a while after submerged. This will emit burnt oil fumes as the bubbles reach the surface. I don't remember the information, but there was a recommended volume of oil related to the size of part, so that the quench was adequate. I remember determining that a 45 gal. drum was large enough to do anything I would ever want.
If you have ever tried lighting engine oils, you will find them hard to start. To ignite them most people mix in a generous amount of diesel oil or you can use a wicking method like placing a paper towel in oil and allowing the flame to transfer from the paper to the oil. I have never been concerned with the ignition of my drum of oil (comprised mostly of 15-40w), though I do keep several extinguishers around the shop. As mentioned, my drum has a good fitting lid, and if there were ever to be a problem my response would be to drop the part and put the lid back on. To get an idea of the kind of fire fighting conditions you could face try some small controlled experimentation.
