Which of the following is a good technique when using a fire extinguisher?

Answer 1

The best technique is to let someone who knows what they're doing do it. It's surprising to many people how hard a relatively small fire is to put out. When I was in graduate school we had a required fire safety class, and they set a 4 foot square pan of gasoline on fire and let us try to put it out. About half the class was not able to do so before their extinguisher ran out, and these were chemistry graduate students who understood the whole "how fire works" thing from a theoretical standpoint pretty well. Several people wound up blowing burning gasoline out of the pan, which obviously would have been really bad if the area around the pan hadn't already been cleared of anything flammable for a considerable distance.

For the record: aim at the base of the fire and sweep from side to side, not too fast and not too slow.

Not that that will likely help much; they told us all the same thing beforehand, and only about half of us were able to make it work anyway. The point they were making is that if a fire occured in your lab, unless it was trivially small, calling the campus fire department immediately was almost certainly a better use of your time than futzing about with a fire extinguisher.

Answer 2

Direct the extinguisher at the base of the flames using a sweeping motion