Fire Extinguishers

A bit on Fire extinguishers: Having fire extinguishers in the shop is of course a great thing. So some fire extinguishers truths. A 10# dry powder extinguisher will spray for 9 to 13 seconds if you squeeze that handle and hold it. Yep 9-13 SECONDS. Unlike the movie guns that shoot forever without reloading, a fir extinguisher does run out, and quickly. Fire extinguishers are for "Incipient stage" fires. The firemen will tell you that is a small fire that is in the early stages.

Sooo... if a 10# sprays for only 9-13 seconds what use is it? If you catch a fire early 9-13 seconds of dry powder, sprayed at the base of the flames where the fuel is will usually put out a small fire.

Lets talk types of extinguishers. A bucket full of dry sand is works on metal fires but not at all on burning liquids. A bucket of water works great on burning wood or paper, but gets very exciting on electrical fires or burning liquids. So the folks that make the rules have a system where extinguishers are rated. 
type A is for burning solids like wood, paper and the like
Type B is for burning liquids like oil
Type C is for Electrical
Type D is for burning metals

Now if you go to the big box store you will find type A-B-C extinguishers. They work for all 3 and are the best choice for those of us who don't work with metals that will burn like magnesium.

So how do extinguishers work? Think of a fire as a 3 legged stool. It can only stand if all three legs are present. Fire needs three things to exist, Fuel, Heat and oxygen. Take any of the 3 away, and the fire can't burn. So when you toss a bucket of water on burning wood, the water flashes to steam pulling the heat out and no fire. Dry powder coats the fuel and prevents oxygen from reaching the fuel. A CO2 extinguisher blankets the fuel with extremely cold CO2, which both cools and excludes oxygen.

So now that we understand how the fire works and how to kill it, lets talk some practical bits about fire extinguishers. First the very best way to use a fire extinguisher is have it hanging on the wall and never use it. That's right never use it. We achieve that by planning and some discipline on our own part. Keep your shop as clean as you can of things that can burn. Bits of paper, rags etc. Stay in the shop and cleaning up for 30 minutes after any hot work achieves both a clean shop and some one observing for a fie that is smoldering. If you are going to quench with oil, keep the oil totally free of water, as it can flash to steam and cause a flaming eruption of oil. ONLY use a metal container with a good fitting lid for oil quench. Use a size container that will both contain the oil and the item being quenched if you drop it, and consider the volume of oil needed to pull out the heat. Quenching knives is much safer in a 5 gallon bucket of oil then in a quart.Plan a safe route out of the shop when quenching. I like to hang an extinguisher by every exit door of the shop. That way I can leave the shop, stand at the door and grab an extinguisher and THEN decide, in safety, if this is a fire I can handle with my 9-13 seconds of spray.

For those with hydraulic presses, these can be very useful machines, and also can present the threat of a fire throwing shop destroyer if a leak sprays hydraulic oil onto hot metal. These fires are usually not a single extinguisher type fire, but there are a couple of things one can do to make them maybe fight-able. Rig an E-stop that is at the door of the shop. That way, if the beast starts flame throwing you can retreat, slap the E-stop at the door as you exit. Once the pump stops, the pressure drops and then you have an oil fire not a flame thrower shooting flaming oil across the shop fire. You most likely still have a major fire and 911 is the first thing, then extinguishers from a safe exit point will maybe save the shop till the fire dept gets there. ( Note, this is not a theoretical fire issue, I have cleaned up several in industrial forges. Hydraulics are a blessing that carries the absolute, no if 
s,ands, or buts of leaks. All hydraulics leak. The only question is when and how much)

Sooo... you have you nice BIG 10# type A-B-C extinguishers at the doors and you get a fire. How do you use the extinguisher? Many folks use the P-A-S-S memory trick. That is;
Pull the pin
Aim at the base of the flames
Squeeze the handle
Sweep the spray a bit to fully cover the fuel.
I like to remind folks that the extinguisher is usually hanging on a pin. you have to LIFT the extinguisher to get it off the hanger. Now you are thinking the old guy has lost it. I have had to replace many hangers hat were either ripped off the wall or bent where in the excitement of a fire the folks forgot to lift and struggled a bit to get the extinguisher off the wall.

So you get that 10#er to the fire, what is this sweep stuff and how far do I stay away to do the job? You will hear things like 6-8 feet. I use Reinhardt's rule of eyebrows:
If you are spraying and hitting the fuel, you are close enough.
If you are hitting the fuel and your eyebrows are burning off you are too close.
If you are spraying and not hitting the fuel you are too far away.

What about care and feeding of your extinguishers? In industrial settings where a fire extinguisher tech is caring for your equipment they will check the overall condition monthly, checking that the Gage shows charged and no damage has occurred. CO2 extinguishers are high pressure compared to dry powder, and since the CO2 is liquid and flash to gas during use the Gage will show the same pressure till all the liquid has become gas before dropping. These have a TARE weight stamped near the valve mount. You add the tare weight to the rated weight IE 10# rated and say 6# tare and the extinguisher must weigh that or it has begun to lose charge.
A dry powder extinguisher is turned upside down and shaken vigorously every year at the annual inspection to "Unpack" the powder.Extinguisher get a hydro test every 6 years and often at the design life the extinguishers are pulled from service and sometimes become available to folks like us.They are usually fine, but you have to accept that they are past design life. If you do big festivals and take one there the fire dept folks are often checking an will usually note that they are out of date. I have never had a fire Marshall fail to accept a 5 gallon bucket of water as an acceptable extinguisher for a coal burning forge at a festival.

Last but not least, be aware that when you pull that trigger you get a huge spray of dry powder that flows much like water. Surprises some and they let up. don't let up, spray the fuel till the flames are gone then spray some more to prevent a re-ignite. CO2 will be loud, make a fog cloud and freezing anything in its path. Once yo use an extinguisher ANY, consider it dead till rebuilt. The flow across the valve seat usually damages the o-ring and the will leak down over time from that point. Dry powder is basically baking powder. It is NOT good to breath, and is corrosive to things like electrical panels and aluminum, so once the fire is safely out, start cleaning it out if possible or the panel is still savable.

Last, remember, things can be replaced, you can not be replaced. First GET out to a safe spot, look and call 911, and then fight a SMALL fire from the safety of a clear exit path and a good charged extinguisher.

Written by Jeff Reinhardt