Death by Teacher

All the facts are not in but yesterday a student died and several students were injured in an explosion at a school. One report stated that a barrel was being cut open to make a barbecue …

I was not there and don’t know the technique being used but Welding 101 is that when cutting any container that held a flammable substance or may have held a flammable substance either

  • steam-clean the container to eliminate all flammable substances or
  • fill the container with water or inert gas to eliminate oxygen within.

An explosion makes it seem likely that a poor technique was used. In a barrel, for example, all it takes is an air-fuel mixture to be ignited in a confined space and the thing creates a fire-ball at least and may rupture the barrel sending pieces outward at high speed. A person nearby may receive a severe blow, burns or shrapnel.

I have been a teacher for a lot of years and I have made mistakes. Any time there is a potential for injury a teacher must make precautions to eliminate the possibility. Doing something that has been done before without disaster is no guarantee that the next time will not result in death and destruction. I would bet some hard lesson has been learned but at too high a price.

see CBC – Ottawa student dies after explosion at school

see Ottawa Citizen – Explosion at high school kills Grade 12 student

UPDATE
“A spokeswoman for the Ottawa-Carleton District School Board told CBC News the board is reviewing its safety policies and procedures following the incident.

“We are asking schools to avoid the use of cutting and welding equipment on enclosed containers of unknown origin, particularly those which are being recycled from their primary intended use,” Sharlene Hunter said in an email.”

Amen. Welding 101…

see CBC – Probe into fatal school blast looks at oil drum

Here is an excerpt from a US Navy welding manual:

CUTTING ON CONTAINERS
Never perform cutting or welding on containers that have held a flammable substance until they have been cleaned thoroughly and safeguarded. Cutting, welding, or other work involving heat or sparks on used barrels,drums, tanks, or other containers is extremely dangerous and could lead to property damage or loss of life.

Whenever available, use steam to remove materials that are easily volatile. Washing the containers with a strong solution of caustic soda or a similar chemical will remove heavier oils.

Even after thorough cleansing, the container should be further safeguarded by filling it with water before any cutting, welding, or other hot work is done. In almost every situation, it is possible to position the container so it can be kept filled with water while cutting or other hot work is being done. Always ensure there is a vent or opening in the container for the release of the heated vapor inside the container. This can be done by opening the bung, handhole, or other fitting that is above water level.

When it is practical to fill the container with water, you also should use carbon dioxide or nitrogen in the vessel for added protection. From time to time, examine the gas content of the container to ensure the concentration of carbon dioxide or nitrogen is high enough to prevent a flammable or explosive mixture. The air-gas
mixture inside any container can be tested with a suitable gas detector.

The carbon dioxide concentration should beat least 50 percent of the air space inside the container, and 80 percent or more when the presence of hydrogen or carbon monoxide is detected. When using nitrogen, you must ensure the concentration is at least 10 percent higher than that specified for carbon dioxide.

Carbon dioxide or nitrogen is used in apparently clean containers because there may still be traces of oil or grease under the seams, even though the vessel was cleaned and flushed with a caustic soda solution. The heat from the cutting or welding operation could cause the trapped oil or grease to release flammable vapors that form an explosive mixture inside the container.

Again, nothing new, just stuff that has been known in the trade for many years. This stuff is from
Steelworker, Volume 1
NAVEDTRA 14250

About Robert Pogson

I am a retired teacher in Canada. I taught in the subject areas where I have worked for almost forty years: maths, physics, chemistry and computers. I love hunting, fishing, picking berries and mushrooms, too.
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6 Responses to Death by Teacher

  1. Yes, acetylene is dangerous stuff. Thanks for the tip. I normally use propane for cutting and it is not quite as energetic. Acetylene is an explosive all by itself.

    I know a guy who was a foolish young man and tried to have fun filling garbage bags with acetylene for “fireworks” one went off spontaneously and he was deafened. I am amazed that young men like that actually survive to adulthood. I was once on a date with a young lady who brought into the conversation a story about a guy filling garbage bags with acetylene and floating them above the city. I, being a foolish young man at the time, chuckled. That was the end of that date. It was her ex-boyfriend and she did not want to make the same mistake twice. Acetylene is very dangerous stuff …

  2. oiaohm says:

    Really after the errors I have seen. Presume a drum or other wise closed is explosive even if new or never held fuel.

    One of the nasty ones I saw personally was a case of the cutting torch going out. Result was the acetylene end up in the drum. So when cutting touch was relighted was now a live bomb.

    What had happened was the O2 had run out. And the acetylene was coming out at a speed it put the flame out. Then basically blew acetylene into the drum through the cut so turning the drum live. Yes this all happens very quickly.

    Yes the drum was brand new and clean before the cutting operation. The guy was lucky the fragments missed him and everyone near by including me. This was cutting drums for cattle feed holding. So person had done a lot. Reason for running out of gas.

    US Navy welding manual basically does not cover gear failure that taints the can from the cutting tool. This flaw is risky.

    So their is a chance the teacher was working by the USA mil and metal workers manual and got caught out by this one.

  3. Yes. That is why old guys who have made plenty of mistakes and lived get to be teachers. Oops. With the recent wave of professionalism in education, young folks fresh out of university with little real-world work-experience get to be teachers and old guys like me usually don’t get to be teachers… In the old days experience counted for something but it’s not respected much in education. In the 1990s, the provincial ministers of education got together and decided a teacher had to have two years of training in the faculties of education plus years’ more education to become teachers. Typically young teachers have five years of university and little or no real-world experience. They don’t know what they don’t know and make big mistakes. They know all kinds of theories about education but much less about the subject matter they teach. For example, there are teachers of physics around who have never studied physics at university and instructors of welding who were top of their class but never worked as a welder. It’s embarrassing sometimes.

    In my case I worked doing maths and science and technology before I went to the faculty of education. I have worked in sweat-shop factories, a university, a hospital, been in business for myself and been a house-husband. I bring a lot of experiences outside of education to education. I know not to make sparks in an explosive atmosphere.

  4. Ray says:

    Sigh… even the best percaution results can result in death.

  5. True. Many lives are saved because fuel-air mixtures have to be close to optimal to get rapid combustion with maximum release of energy. Some people are unlucky and their mistakes are costly. What allows people to become lax about safety is that under apparently similar circumstances, a practice that is safe dozens of time may be lethal another time. Things like air temperature can make dramatic changes in the flammability of a liquid in equilibrium with its vapour.

    There are other traps that surprise people like welding next to concrete. The heat releases steam and the welder gets a surprising explosion of steam. Fuel tanks are a big killer though because volumes can be large. Sometimes people weld inside the tanks or direct sparks in through an open vent/fill pipe or through the joint being welded.

  6. Richard Chapman says:

    It only takes a small amount of fuel (in the right conditions) to make a big explosion. A tablespoon is enough.

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