DCHAS-L Archives, Jan 23 2018 - Re: [DCHAS-L] Benzene flammability teachable moment

Ralph, you touch on a concept that I think has eluded chemistry instruction for decades. I remember many years ago teaching my high school chemistry students about the chemical reaction 2KClO₃-a` 2KCl + 3O₂. I'm not even sure what the lesson was about (activation energy? Example of a decomposition reaction? Bond energy? Maybe it was simply balancing equations). Anyway, I remember thinking, I could explore so many chemical concepts with this equation, but do any of the topics in my course suggest that this reaction has the potential to burn their eyebrows off? In other words, after I've analyzed every conceivable aspect of a reaction, what does this actually look like in person?

The Next Generation Science Standards relating to high school chemical reactions are found at this link:

https://www.nextgenscience.org/topic-arrangement/hschemical-reactions

As you see, much of the student work (developing models, constructing explanations) focus on the level of particles and bond energy. It seems like it could be a logical next step to relate these models and explanation to the macroscopic situation; specifically, based on what we've concluded about bond energies, rates of reactions, etc, etc, witll this reaction explode? Will the reactants or products burn me? This isn't just safety in science instruction; it's safety as science instruction.

Eddie McGrath

Edward J. McGrath

Supervisor of Science

Red Clay Consolidated School District

1502 Spruce Avenue

Wilmington, DE 19805

(302) 552-3768

We did not inherit the Earth from our parents. We borrowed it from our children.

From: ACS Division of Chemical Health and Safety [mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU] On Behalf Of Jeffrey Lewin
Sent: Tuesday, January 23, 2018 9:10 AM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Benzene flammability teachable moment

I can share a personal one from High School. I worked in a restaurant that deep fried everything (fish, fries, hushpuppies) so we had lots of deep fryers. The oil was regularly drained, filtered then returned to a fryer (there was succession, shrimp got the freshest oil, while panko fish got the oldest oil). The fryers were gas heated and the gas was turned off during the draining process. After refilling the fryers we relit them. But not with a long-handled lighter; instead, we would tightly roll up some paper towel, dip it in the vegetable oil, and light it like a wick, using that to reach into the guts of the unit to light it.

Fast forward to high school chemistry class where I was explaining this to one of my fellow students. They didn't understand the wick part, so I showed him by rolling up the paper and sticking it in the nearest liquid...acetone. The results were predictive as the paper towel flashed in my hand, fortunately not injuring me (and, fortunately for me, not catching anything else, like the acetone bottle, on fire). A good lesson in flammable/combustible, flashpoint, and volatility differences in liquids.

I think back to that incident when I hear about the Rainbow disasters and sometimes wonder if part of the problem is Uncle Joe. Everyone has been to Uncle Joe's BBQ where the charcoal isn't heating up fast enough, so in spite of the instructions on the bottle, he adds more lighter fluid to the charcoal. Unlike the methanol bottle, the differences in volatility, flash point, and the fact that the squirt bottle design makes a natural flame arrester, Uncle Joe usually gets away with it, or suffers singed eyebrows rather than exploding bottles.

If you want to spend 14 minutes wondering what guardian angel is watching over him, watch this YouTube video as a guy deftly sticks lit matches into (fortunately full) Mason jars of various fuel oils, jet fuel, and gasoline...had the jars been half full and a hot day, he might not have been so lucky...

https://www.youtube.com/watch?v=7nL10C7FSbE

Jeff

On Tue, Jan 23, 2018 at 8:27 AM Stuart, Ralph <Ralph.Stuart**At_Symbol_Here**keene.edu> wrote:

I am very interested in identifying opportunities to use safety examples to illustrate scientific principles as a teaching strategy for both safety and science.

Along these lines, a colleague shared this anecdote with me during a discussion on a different topic:
"I had a very cautious student take a heat gun to a flask of frozen benzene to warm it up. They were truly surprised by the fire that resulted."

It was not intuitively clear to me what was going on here until I looked up the melting point of benzene (42 degrees F) and the flashpoint (12 degrees F) and saw that solid benzene is still flammable. Am I correct in interpreting this to mean that frozen benzene is sublimating enough gas to support a flame if the vapor doesn't disperse too quickly? This seems to me like an opportunity to connect the scientific concept of sublimation to a memorable lesson by using safety data and connect science and safety in an educational way.

I wonder if other people have similar examples of Science taught through considering Safety Scenarios.

Thanks for any thoughts on this.

- Ralph

Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
603 358-2859

ralph.stuart**At_Symbol_Here**keene.edu

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Jeff Lewin

Chemical Safety Officer

Compliance, Integrity, and Safety

Environmental Health and Safety

Michigan Technological University

Houghton, MI 49931

O 906-487.3153

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