Oxy Acetylene Safety Tips
Oxy acetylene and high pressure oxygen cylinders, in general, have the potential to be extremely dangerous, but they’re safe if they’re used with caution, common sense and you play by the rules.
Let’s start with oxygen. Oxygen is a gas and a new bottle is usually filled about two thousand PSI give or take. That’s about one hundred and forty bar and that’s a lot of pressure. To get that down to something we can work with we need a regulator. The regulator is the thing that looks like a clock stuck to the top of the tank. Welding regulators have two gauges. Usually the one closer to the valve tells you the pressure in the bottle or the cylinder as the pros call them. The other gauge tells you the working pressure coming into the hoses. Welding regulators are adjustable, you turn the knob to change the working pressure.
Now let’s have a look at the acetylene bottle. Acetylene isn’t a gas, well, it is, but it’s dissolved in a liquid, it’s dissolved in acetone. Acetylene is unstable above 15 to 20 PSI so it can’t be shipped on its own like oxygen. Let’s have a look inside. Inside the steel shell of the cylinder is a porous matrix. Kind of like that big hard sponge you have in the utility sink. The matrix is filled with acetone. Don’t quote me on this, but it might be about 50 percent acetone. If you want exact details do a Hey Alexa or Hey Siri search for acetylene bottle matrix/acetone percentage. The acetylene gas is dissolved in the acetone, sort of like CO2 is dissolved in your soda before you open it if that makes sense. When you crack the can open, the CO2 starts to bubble out and that’s more or less what happens with acetylene, that’s what keeps it stable. That, by the way, is also the reason you should never use acetylene bottles that have been laying on their side or after they’ve been laying on their side, like in the trunk of your car, you should let them settle overnight or so. Now, I know there’s someone who will say that they’ve used their acetylene bottle upside down hanging from the ceiling for the past 30 years and nothing bad has ever happened. The point is, you shouldn’t do it, it’s very dangerous. Anyway, just like the oxy bottle, this also has a regulator, the scale is a little bit different because of the operating pressure of acetylene, but it’s the same principle.
Let’s get into the numbers now. Just like the wonder twins, acetylene and oxygen on their own are absolutely marvelous, but when you put them together, that’s when the magic happens.
Acetylene is C2 H2 and oxygen is O2. When you put those together and burn them like any hydrocarbon, you get carbon dioxide and water, CO2 and H2O. I’m sure you probably get all sorts of other weird stuff, but the majority will be CO2 and H2O.
We have more C2, H2 and O’s on one side than we do on the other. Let’s see what happens when we try to balance our equation here. It’s been awhile, but we’ll start with the O2. That looks easy. Sitting there all by itself on the left, we have one O2 oxygen atom. On the right we have two in the carbon dioxide and one of the water. So there’s 3 there. We can’t add another oxygen by itself on the left. So let’s double the H2O just to even it all out. Now we have four oxygen. All right, we’ll add a two on the left to get us to O2’s. So four oxygen atoms on the left, four oxygen atoms on the right. And when we double that water, we also doubled the hydrogens. So let’s double the number of hydrogens we have on the left in the acetylene into H 2’s on the right in the water. So now what happened? We’ve got the oxygen sorted out, got the hydrogen sorted out. But when we doubled, the H2’s on the left we also doubled the carbons. We essentially have four on the left in the acetylene and one on the right in the CO2. So let’s put four carbon atoms on the right hand side to match the four carbon atoms on the left, just like before we fix the carbons. But we broke the oxygen’s on the right, we now have 4 O2’s from the carbon dioxide and 1 O from the water for a total of 5 oxygen pairs on the right. Just change our 2 to a 5. We have the same number of carbons, hydrogens and oxygen’s on the left as we do on the right. Now, if you’re wondering why I went through all this, I can’t blame you. But take a look at what happened. In order to get complete combustion of the acetylene and the oxygen for every two parts of acetylene we need five parts of oxygen to completely burn it, and if we set up our torch to do that and meter those proportions of acetylene and oxygen, we end up with what’s called a neutral flame. When we light up, a neutral flame produces carbon dioxide and water. Alternatively, you could adjust the torch, so you have an excess of oxygen or an excess of acetylene. If you have too much oxygen, you have an oxidizing flame, if you have too much acetylene, you have a carbon rising flame.
All right. We’re not quite down to brass tacks, but we are almost cooking with gas. I picked up some new tips for my torch. Tips need to be cleaned with a special tip cleaner, but sooner or later they wear out and you need new ones. Remember keep your tip clean, get comfortable before you start, and concentrate on the cut while it’s happening. Good brands of tip cleaners include Victor, Irwin, US Forge, and Tech Team https://techteamproducts.com/. We like Tech Team’s 762 Tip Cleaner Set because it has all the correct size reamers, a file, and it comes in a handy storage case. https://www.amazon.com/Tech-Team-Long-Pattern-Cleaner-Oxy-Acetylene/dp/B07NGV9CS2/ref=sr_1_1?keywords=tech+team+tip+cleaner&qid=1553187220&s=gateway&sr=8-1. Tips are sized by orifice diameter, either the size of the hole or some made up number like a number two or a number four. What you need is three different nozzles one each for heating and welding or braising and cutting. The largest one is the one that gets the most use for heating and braising. You kind of want a large soft flame instead of a needle like the pinpoint you might want for welding.
Now the torch has two knobs on it, one for each gas, and I’ll be using both to adjust the balance of the flame. Because I will be using a smaller tip, I’ve also dropped the pressure at the regulators. The working pressures you set on the regulator are based on the tip or the nozzle and sort of based on the work you’re trying to do. The bigger the work, the bigger the tip, the higher the pressure. Check the literature from your torch manufacturer to find out exactly what pressures those should be. Those are very important to both your safety and having a good result. Brands like Victor, Harris, and Forney provide good information.
You should use a striker to light up your torch. The safest and best way to light your oxy acetylene torch is to use a flint striker. Basically, this is a device that has a flint member that is fixed into a threaded socket that screws into a spring loaded member that moves back and forth against a hardened steel surface like a file. This assembly is held inside a protective steel cap about 1” in diameter x ½” deep. When the striker is activated by hand pressure, the flint moves across the steel file and creates sparks. These sparks, of course, will ignite the acetylene, and the steel cap will keep the flame from unexpectedly projecting too far. These strikers are made by many companies such as: Forney, Hobart, Ally Tools, Vas Tools, Hot Max, US Forge, Lincoln Electric, Worthington, Levado, and Tech Team https://techteamproducts.com/. Tech Team’s model 763 Flint Striker https://www.amazon.com/Lighter-Igniter-Oxy-Acetylene-Tech-Team/dp/B07NGS8PLY/ref=sr_1_33?crid=2QQKZ0LGHZBCF&keywords=flint+striker+welding&qid=1565098867&s=gateway&sprefix=flint+striker+welding%2Caps%2C124&sr=8-33 is the one we like the best because it has high quality construction with a durable zinc plating, and it contains 3 flints that can easily be rotated one to the next to the next as it wears down and becomes ineffective.
It probably also occurs to you that eventually these flints will wear out and oddly enough there are several companies that make replacement flints such as: Forney, US Forge, Shurlite, Zippo, and Tech Team https://techteamproducts.com/. We happen to like Tech Team’s item 761 https://www.amazon.com/Replacement-Strikers-Oxy-Acetylene-Tech-Team/dp/B07NGNFK2V/ref=sr_1_1?keywords=tech+team+flint&qid=1565108056&s=gateway&sr=8-1which contains 3 sets, each set having 3 replacement flints, which easily fits into their 763 3 Flint Striker. I’ve always been taught not to light a torch with an open flame like a lighter and I’m not exactly sure why that is. The only thing I’ve ever been able to think of is maybe the torch pressure could blow out your open flame like you try to light the torch and it just blows the lighter out like a birthday candle. Then you might be in a situation where you’ve got your torch, putting out a deadly mix of acetylene and oxygen and you’re trying to strike your lighter.
Slowly open the oxygen up and you may, or may not, see three flame cones, the outer cone, the inner cone and the smallest one nearest the nozzle. You can continue to open the oxygen until that middle cone and the small cone sort of become one. Now there’s something else going on here you may have never thought about. The flame is conveniently staying put. It’s attached to the tip of the nozzle. Now, what’s happening is there’s a flame front. The flame is trying to burn its way up that gas, sort of like when you light a fuse. The flame isn’t moving because the gas is coming at it as fast as it’s trying to burn it. In our fuse analogy, the fuse is moving closer to the fire at the same speed that the fire is trying to climb up the fuse. So we have a bit of a balancing act, the gas coming out, the nozzle, at a certain speed and the flame trying to burn its way back into that gas. If the pressure is set too low on your regulators you could end up in a situation where that flame speed exceeds the speed of a gas and the flame comes into the nozzle, comes into the torch, and it starts to burn its way up that fuse back to the bottles. The term for that is flashback, in your lines. At some point, maybe two points, you should have installed thermal check valves that should break the link if a flame makes it this far back in the tubing.
When you light the torch start with the acetylene. Some people like to open both valves so they’re not getting as sooty a flame and making a mess. But that’s actually quite dangerous. The acetylene on its own at the pressures you will be welding with isn’t as dangerous as an oxy mix. To keep it from making such a mess just open it up a little bit more. A small flame will start to clean up slowly as the oxygen reduces the acetylene to get the balance right to get us to a neutral flame.
I’d hoped this would go without saying, but I’m gonna say it. The flame is very hot. I mean, if you’ve never used an oxy acetylene torch before, you likely have no real reference for just how hot this thing is. Take my word for it. Be very mindful of where you point this thing. I know, I know, it’ll be just a second. You just need that one thing a couple of steps away. You’ll just put the torch down and be right back. If it’s not in your hand, turn the torch off.