I am trying to come up with best possible evidence for young unbelieving students that will explain to them about oxygen and its relation to flammibility. Can i get some expert advice on the matter. Remember, we are talking about highschool students.
Victor... A brand of Oxy-Fuel cutting and heating equipment has a video that covers safety matters very well. They use an example of a slightly smoldering shop cloth and how it behaves in ambient air and how it reacts to pure O2. (nice flameup) Your local welding supplier can get hold of this training video for little or no cost. It's one of the few training videos out there with no mistakes.
Oxygen by itself is not flammable; it accelerates combustion.
Oxygen can convert moderately flamable materials into highly flamable ones. The higher the pressure the more effect. Coal dust soaked in liquid oxygen can be used as a blasting explosive, the blasting cap provides the high pressure to start things off. Years ago a NASCAR pit crew ran out of nitrogen to run the air wrenches. Someone decided to try oxygen, hit the trigger to test, 10 feet of flame (as I heard it) from the burning lubricant out the exhaust. One of the high school chemistry tests for oxygen is to place a smoldering pine splinter into the container, if it bursts into flame oxygen is indicated. The trick here is to make it spectacular enough to get the students attention but controlled enough to keep the room intact.
Bill
fbrieden has it right, O2 is not flammable at it's own rate, it aids in combustion that has already started. Bill, I'm not sure how the NASCAR impact wrench shot flames, the lubricant did not ignite just because O2 was used to spin the motor, furthermore the inside housing on the air motor is all made from aluminum and the veins that propel it are made from a fiber material. O2 needs to be handled with care and common sense, not fear or lack of knowledge.
MDG
You are wrong about the impact wrench.
Oil can and will ignite spontaniously in the presence of high pressure o2.
A good friend was seriously injured in an industrial accident when o2 was mistakenly introduced into a piece of process machinery which was designed to accept an inert gas.
The oil present in the piping exploded and blew half of his face off.
How high of a pressure are you talking for the oil to spontaneously combust? I'm not sure of exact numbers, but very high performance impact wrenches function under 175-200psi. Is that enough to provoke spontaneous combustion??
Gentlemen,
that's why your tought in oxy-acetylene 101 never to put oil on the threads of oxy-acetylene gauges because it can cause a fire. Lincoln and ABC merit shops offer video classes on this subject and cover this issue.
Jim
High pressure is not the precisely culprit else wise we would not have spontaneous combustion.
It is simple the correct mixture and pressure can assure you of a broad expanse of mixtures. Rest assured, oxygen mixed with petroleum will combust
Not sure how much pressure is involved to cause an explosion; I think it has more to do with sudden pressure or "hammer" effects. But that is the reason that "Use No Oil" is on oxygen gauges. In my past life as a calibration lab manager, we routinely had to send oxygen gauges out for certification to "oil free" condition before they could be placed back into a test system after being calibrated. As a rookie calibration tech, I once had a gentleman come to our lab in a hurry to get his test gauge calibrated. I did it while he waited in the lobby. I took this very expensive test gauge and put it directly onto a dead weight tester, calibrated it and gave it back to the owner with oil dripping out the end. Needless to say, he spent in excess of $300 to have it cleaned and recertified oil free. Learned my lesson right then about proper, conscientious handling of oxygen line components.
That leads to another question. How much is to much (oil) when you are talking about keeping your oxyacetylene equipment and lines clean and grease free. The shops i have been associated with were always filled with grease and grime to one extent or the other.I know that contractors that install new oxygen and acetylene lines and manifolds adhere to some strict guidelines, (codes) when it comes to cleaning and testing on new instalation. TSP (Tri-sodium- phosphate) i believe is a common industrial degreaser used to clear out any grease or debree in new lines. So my question is, what should be the red flag that tells a shop owner that his oxy equipment needs servicing and cleaning?
Use a OAW torch and a length of 1/8" diameter steel filler rod clamped in a vise. With a neutral flame, heat the end of the rod to near melting and then shut off only the acetylene torch valve. Play the tip with oxygen flowing on the heated wire. The wire disappears with no flame. Be very careful, and I would caution setting up an explosion demo. Use two rags, one rag clean and dry a second saturated with oxygen. Use a flint striker and one is going to ignite and the other will not. Practice & Practice the demo you will use, don't experiment in front of students.
I remember a very simple demonstration from chemistry class that was part of an experiment designed to identify various gases produced from different chemical reactions.
Basically, the demonstration was done with a piece of wood that was lit on fire and then blown out so that the splint was smouldering. This was then inserted into a test tube that had oxygen in it. The result was that the wood instantly burst into flame when exposed to the high concentration of oxygen in the tube.
I was thinking this could be set up safely and easily, and will clearly show what happens when oxygen reaches smouldering flammable materials. (I still shudder when I see someone using oxygen from a cutting torch to blow off their clothing.)
Chet Guilford
PS - in my reading of this post, I somehow did not notice billvanderhoof's (and others) post that says the same as I just posted. Sorry 'bout that.
Bill,
Our instructor filled two baloons to normal size. One was filled with Acetylene only and the other with an extinguised neutral cutting flame. The tied ends were placed in a vice and the torch lit. the first was a boom, but the second shook dust off of the overhead lights. Very noticable.
gls
Don't try this one at home kids!
Don't try this one in the shop pros!
Don't try this one in the classroom educators!
Forgive me Lawrence and all, for this should not be tried by anyone.
Sometimes I must try harder to remember that this is a public forum wherein accounts and examples may be told without specific metion to context simply because I will assume that all will know the context. I unintentionally replied only to the question of "What does oxygen do to combustion?" rather than answering the entire question of "What are good examples of what oxygen does to combustion?" without realizing that they are not separate questions.
Again, there are no excuses for my hasty and ill-considered reply. Forgive me and thank you for catching my slip of the tongue.
gls
Just a quick safety note to anyone who tries to duplicate the expieriment that gls mentioned...
While it works wonderfully, and creates an awe inspiring boom, (especially when you use garbage bags) all it takes is one spark of static electricity to set it off. The "bomb" doesn't care if it is still in your hand or not when it ignites.
There was an article in the news recently that showed a picture of a car that some fool tried to tranport a garbage bag oxy/acetelyene bomb in. Evidently, when they tried to put it in the car, the bag rubbed against the cloth seat, which created a static spark, and ignited. Needless to say, both the car and the fool were blown away.
Stay safe,
Tim
I also learned of perfect gas mixtures in coke cans in shop class. One day we took 3 tennis ball cans and cut the end out of the middle one. Taped all three together. Set our torch perfectly and wiped the flame out. Filled the cans with gas mix. Had a long firecracker fuse out of a string of Black Cats for ignition. We set this off outside of the shop class in the parking lot. It made a HUGE BOOM. We ended up having the Ft.Worth bomb squad investigating the blast. Mr. Owens just KNEW who did it and told us that we better not EVER tell anyone what we had done and better never even blow up a coke can in his class again. That was close to 30 years ago and I remember it like it was yesterday. Nowdays I have some cannon fuse I ordered from the army surplus store and I use those gallon+22oz size detergent bottles. Only do them during firecracker season and only if it is really damp outside. What was said about static electricity is true and I get VERY nervous picking those bottles up to put the lid on them and carry them outside. I always have my weldering gloves and coat on, safety glasses and face shield, and hold them as far away from me as possible. But I know if one ever goes off in my hand I'll probably lose it and will be lucky to survive the blast at all. I just can't help it though. They make such good firecrackers and are SO impressive!
Hard to top that one.
Bill
Worked with a guy who was using a framing nailer and didn`t have enough air hose to reach his work area.This nailer had been used earler in the day and was giving some problems so a good constant hosing down with WD-40 helped greatly.So to get around the air hose problem he hooked it up to a bottle of oxygen and when he opened the valve on the tank.Well lets just say all that was left was the handle and what parts where embedded in his upper body and one nice size bill for a life flight ride to the hospital.
Regarding the question "how much oil/grease is too much", had a recent incudent where a nurse was changing a patients oxygen cylinder and whiped the reg seating area with her fingures to make sure it was clean.
When she opened the cylinder valve there was a bit of a pop followed by some black smoke.
The culprit, she'd had a McDonalds at lunch time and hadn't washed her hands before changing the cylinder, so as you see ANY OIL/GREASE IS TOO MUCH
When I was in school I remeber our shop teacher making the point with two rags. He said "these both represent the clothing you are wearing. Now, you get some shop dirt on you and the most convienant source is oxygen to blow off the dirt. What you're actually doing is super saturating your clothing with oxygen. Now you walk over to the grinder a minute later and..........." He then waved the shop rag behind the grinder and it lite up quickly. The other rag would have give you plenty of warning with a hot spot but not violent ignition.
It made a good impression but not such that we wanted to play with itl. I'd be worried about plastic garbage bags. I can see everyone wanting to get a big bang of their own.
Lesson learned so far,,,, handle regulators with clean hands and dont blow the dirt off ur clothes with the oxygen from a cutting torch. :)
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