I'm currently working on a couple home-made blades and I have some questions for anybody who has heat treated O2 steel at home.

I found the following on the Hock Tools web site:

When it's hit critical temp, remove it from the heat and quickly dunk it into a sufficient quantity of oil (preheated to about 150F.) Swish it around a bit until it's cooled then let it cool to ambient in the air.
So, here are my questions:

[1] What type of oil is best to use? I've read everything from automatic transmission fluid to peanut oil.

[2] My understanding is that one wants to use a lot of oil so as to reduce the chance of flash fire when the hot metal hits the oil. How do I heat up a couple gallons of oil without risking fire?