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.
“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…
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