I mentioned it in the other fire thread, but be aware of the limitations of CO2. They are a good option to have in a shop but are BC only extinguishers meaning they have minimal effect on class A (ordinary combustibles, wood, paper etc). They will knock down a fire in wood or paper, but rekindles are very likely if not followed up with water or other means of actually cooling the material. We used to let people use a CO2 to put out a fire in stacked wood, leaf pile, waste basket full of paper and wood scrap, and in many cases once the CO2 dispersed (a few seconds) the fire came right back. You can have the same issue with flammable liquids on hot metal.
Dry chem is very messy, but ABC dry chem extinguishers are very common because they work. The dry chem forms a crust over the burning material which smothers the fire and give the agent lasting effect. The mess is not being exaggerated though, you can expect to spend days cleaning up the powder, and will probably continue to find powder for weeks in the nooks and crannies of your shop.
CO2 is great, and good to have available, just know you may need to repeat applications, and do not leave an "extinguished" fire until you have thoroughly checked it and ensured it is 100% out, then check it again (this goes for any extinguisher). Always have an ABC dry chem available as back up in case the CO2 can't finish the job. CO2 can also displace oxygen so after use make sure you ventilate the shop well and avoid low spots where it might accumulate.
If you have wood or paper in the shop do not overlook the effectiveness of the good old pressurized water can extinguisher on ordinary combustibles, and even has some effectiveness on flammable liquid coated / soaked materials (not so much on pooled liquids). Easy to use (basically a big squirt gun) and you can refill it yourself if you have an air compressor. A strategically hose reel and garden hose can also be quite effective. Of course with water you want to make sure you don't get into energized electrical equipment.
If you do have a fire and are not 100% positive that it is out, do not hesitate to call the fire department. Let the 911 dispatcher know the fire has been extinguished so they don't race across town with red lights and siren, but in most communities there is no issue in having an engine company come out and make sure you got everything. They can also help clear out smoke if it was a serious fire. There are a very few communities with private subscription fire services where this may be an issue, but everywhere else it is just part of the job. They are much happier to spend 30 minutes making sure than coming back at 2am when the whole building is engulfed.
