Chemistry explosion

[snopes]

Forensics and school punishments combine in this remarkable anecdote from Athol Greenhalgh, of Narraweena (Column 8, since Michaelmas Term): ''A story from my father who would have been at school in Newcastle in the 1920s,'' Athol writes. ''The teacher was doing a chemistry demonstration at the front of the room using glass equipment. It suddenly exploded, showering the room and students with glass fragments. The students trooped over the road to the nearest doctor and returned to class after repairs had been carried out. The teacher then inspected them all - those with cuts to the back of their heads or behind their ears were promptly caned. They were irrefutable evidence that they had not been paying attention at the critical moment.''

http://www.smh.com.au/column8

[Darth Credence]

Or, they had reflexes and turned away when something exploded.

[snopes]

During a high school science class, we were performing the hydrolysis of water experiment, and the two guys at the bench in front of ours -- who were total goof-offs -- managed to screw something up (allowed the electrodes to touch, maybe?) that caused their beaker to suddenly shatter and throw fragments everywhere.

Neither of these two clowns was wearing his required safety goggles at the time of the explosion. They stood there, stupefied, for a few seconds, and then one of them quickly reached out, snatched his goggles off the bench, and pressed them to his eyes.

[Mr. Furious]

I set my high school Chemistry teacher on fire.

He was doing some sort of demonstration that involved soap bubbles filled with natural gas. Basically, a student was supposed to touch an open flame to the bubble, resulting in an impressive fireball. He'd admonished us not to ignite the bubble when it was close to him. I volunteered, of course, and in my excitement, I ignited the bubble about 6" from him. It set his lab coat on fire, and his quick thinking avoided the gas jet turning into a flamethrower. Nobody was hurt, thankfully, and we all laughed about it afterward.

[mags]

My high school chemistry teacher neglected to follow part of her instructions for setting up an experiment, and it resulted in one of my classmates's test tube of chemicals bursting into flames as he carried it back to his station, while it was inches from my face as he passed me.

There was a rubber stopper in the top, and thankfully it did not burst. We were not required to be wearing safety goggles at the time, because it was not expected to be a dangerous experiment. Afterward my teacher said "oh, that's why the instructions said to let it stop bubbling before putting it out." I'm still a little angry about it.

She did tell an interesting story once about when she was taking high school chemistry. One of the other students stole a small piece of solid sodium from the supply closet, after seeing its volatility in class. He decided the best place to hide it was his back pocket. At some point between classes, perspiration apparently soaked through his pants. A different teacher ended up tackling him in the middle of the hallway, to put out his flaming rear that he had not yet become aware of.

[A Turtle Named Mack]

Originally Posted by mags

She did tell an interesting story once about when she was taking high school chemistry. One of the other students stole a small piece of solid sodium from the supply closet, after seeing its volatility in class. He decided the best place to hide it was his back pocket. At some point between classes, perspiration apparently soaked through his pants. A different teacher ended up tackling him in the middle of the hallway, to put out his flaming rear that he had not yet become aware of.

A friend of mine took a piece of sodium and threw it into a beaker of sulfuric acid, which promptly erupted. It sprayed his girlfriend with sulfuric acid and immediately began dissolving her doubleknit (fashionable at the time) dress. The teacher had to make a deft maneuver of throwing the gf under the shower and seconds later threw her raincoat over the girl.

[jimmy101_again]

Originally Posted by Darth Credence

Or, they had reflexes and turned away when something exploded.

Not a chance. Human reflexes are nowhere near good enough to dodge an explosion. At least not at the range that might occur in a classroom. It would be about as likely as dodging a bullet.

[Darth Credence]

Originally Posted by A Turtle Named Mack

A friend of mine took a piece of sodium and threw it into a beaker of sulfuric acid, which promptly erupted. It sprayed his girlfriend with sulfuric acid and immediately began dissolving her doubleknit (fashionable at the time) dress. The teacher had to make a deft maneuver of throwing the gf under the shower and seconds later threw her raincoat over the girl.

If the raincoat was thrown on her for modesty, that was a bad idea. A few seconds of flushing might not have been enough.

Originally Posted by jimmy101_again

Not a chance. Human reflexes are nowhere near good enough to dodge an explosion. At least not at the range that might occur in a classroom. It would be about as likely as dodging a bullet.

If we were talking about high explosives, then that would be absolutely correct. But we were talking about glassware blowing up during a chemistry experiment. You'll have glass bouncing off the ceiling, desks, or anything else. I've been in a chem lab when glass exploded, and got hit on the back because I had turned when I saw the explosion coming. No, you couldn't avoid an instant shock wave, but shards that could give you cuts wouldn't necessarily hit in the first microseconds.
And if someone was really paying attention, they may have realized "oh crap, it's gonna blow" with just enough time to duck and cover.
I realize my first statement wasn't clear, but it definitely would not be irrefutable proof of not paying attention if you got cut on the back of the head.

[jimmy101_again]

Originally Posted by Darth Credence

If we were talking about high explosives, then that would be absolutely correct. But we were talking about glassware blowing up during a chemistry experiment. You'll have glass bouncing off the ceiling, desks, or anything else. I've been in a chem lab when glass exploded, and got hit on the back because I had turned when I saw the explosion coming. No, you couldn't avoid an instant shock wave, but shards that could give you cuts wouldn't necessarily hit in the first microseconds.
And if someone was really paying attention, they may have realized "oh crap, it's gonna blow" with just enough time to duck and cover.
I realize my first statement wasn't clear, but it definitely would not be irrefutable proof of not paying attention if you got cut on the back of the head.

Doesn't have to be a high explosive. Indeed, guns don't use high explosives. The "high" or "low" of the explosive really has very little to do with the characteristics of this type of explosion. The explosion occurs when the pressure rises to the point that the container fails. Both high and low explosives reach about the same maximum pressure. The only difference between a high and a low explosive (TNT versus black powder for example) is the length of time from ignition until maximum pressure is obtained. Once the pressure is high enough the container will fail and the two explosions are essentially identical from that point on.

The point about ricochet is good though. Injuries would be possible to the back of the head for example.

The velocity of the shards is mostly determined by the rupture pressure of the container. If the container ruptures at a fairly low pressure then the fragments will be moving fairly slowly. At high failure pressures the fragments will be moving at high velocities. Most lab glassware is designed to take a fair amount of pressure. When lab glass fails because it's pressure limit has been exceeded (as opposed to a failure caused by something like a pre-existing crack) the fragments are typically moving much to fast for a person to dodge them.

Human response times to unexpected events are measured, IIRC, in the tenths of seconds. A typical bullet (~1400 MPH, 2000 FPS) will cover hundreds of feet in that response time. A fairly low velocity shard, at say just 50 MPH (~75 FPS) will still cover 7.5 feet in 0.1 seconds. To move your head 6 inches in 0.1 second would require an acceleration of a couple G's, probably enough to snap your neck.

It all really depends on the failure pressure of the container. If the container was up to spec then dodging is out of the question. If the container had a significant structural flaw then dodging is possible.

Exploding lab glassware, that was up to spec to start with, typically severely maims or kills anyone in it's way. It killed an acquaintance of mine in grad school.

[Darth Credence]

RE: jimmy101_again
I would agree with everything that you said there, including that I was using the term high explosive wrong. What I meant, and I was clearly wrong, was the difference between a real explosion and glassware breaking for a number of possible reasons, including dropping it and it shattering and glass being thrown about. I would also speculate that lab equipment at a school in the 1920's may not have been up to today's standards. [hijack]I recall using a glass batch distillation vessel once. We were distilling a relatively low boiling point solvent to separate it from some paraffin. When done, one of the people in the lab picked it up by the neck, walked three steps, and it hit the ground and shattered, throwing glass everywhere. The person who dropped it still held the neck in his hand. No idea when it had been made, but it wasn't new.[/hijack]
Thanks for the human response time info - good stuff there.

[Eddylizard]

One of my high school chemistry teacher was giving a demonstration of how gold leaf could spontaniously ignite in chlorine gas. He had a very lage jar of chlorine, and a piece of gold leaf. Before conducting the demonstration, he patiently explained how gold leaf sticks to anything, including your fingers, and to be very careful trying this.

He then picked up the gold leaf with a pair of tweezers, opened the jar, and dipped the gold into it.

Now guess what happened next? But he was okay after a couple of weeks.

Another chemistry teacher dropped some potassium into a sink by a window. You know that little bit of water that lingers around the sink? It flared a little, then in a panic, he opened the tap to put it out. The curtains caught fire, and the Fire Brigade attended.

The same guy as above decided to demonstrate what setting fire to sulphur looks like. Sensibly, he did it in a fume cabinet. Not so sensibly, he neglected to notice there was a large crack in the glass of the cabinet. 20 kids were taken to hospital as a precaution.

[jimmy101_again]

Originally Posted by Darth Credence

...between a real explosion and glassware breaking for a number of possible reasons, including dropping it and it shattering and glass being thrown about.

That is also a possibility. "Hard" glass (Pyrex, lab glass etc.) and "Soft" glasses can have a fair amount of internal stress. Heat, especially localized heat, can cause glass to fail even when it isn't under pressure or load. Though in that case a person looking at the glass would have no reason to expect that it's about to "explode". When it does "explode" the fragments may be moving relatively slowly. (We once had a pyrex baking dish containng a duck "explode" as it was being removed from the oven. The shrapnel wasn't bad. The couple cups of duck fat falling on the hot oven element was a problem. )

I would also speculate that lab equipment at a school in the 1920's may not have been up to today's standards. [hijack]I recall using a glass batch distillation vessel once. We were distilling a relatively low boiling point solvent to separate it from some paraffin. When done, one of the people in the lab picked it up by the neck, walked three steps, and it hit the ground and shattered, throwing glass everywhere. The person who dropped it still held the neck in his hand. No idea when it had been made, but it wasn't new.[/hijack]

Old glass can be a problem. '20's era lab glass would have been fine in the '20's. A high school may well have been using soft glass instead of hard, to save money. Still, I can't see being able to duck anything that is moving fast enough to actually cut a person.

I had a great HS chem teacher. Early in the year he would fill a 5 gallon water jug up with some hydrogen and air and light it. The bang got everyones attention, and kept it for the entire semester. If the jug had failed there would have been zero chance of dodging the shards since they would have been moving very fast.

[KaiTheInvader]

I had a chemistry teacher who would do an experiment every year, involving filling a pringles can about an inch full of rubbing alcohol, putting the lid on, and putting a lit match in a hole about 2" over the rubbing alcohol. It popped the lid off pretty high in the air and made a loud bang, and one student asked if he could do it with something bigger. So my teacher obliged, and this time used one of those large metal coffee cans. Only this time, not only did the top come off, the bottom came off as well, spilling flaming alcohol all over his desk!

[Stoneage Dinosaur]

The best school chemistry mishap I witnessed was when a girl in my class somehow managed to light the gas tap directly rather than her bunsen burner. The funny thing was her informing the teacher with "Eeh sir, look!" leading to everyone turning round expecting a slight spill or a broken beaker, but actually seeing a four foot jet of flame roaring over the benchtop. The quick thinking teacher dealt with it well, a sheet of paper in front of the tap stopped the flame instantly so the gas could be safely turned off with no harm done.

[Squirt]

My A-Level chemistry teacher used to hand out "Awards for Laboratory Competence" when someone messed up. I managed to get the "Michaelangelo Award for Ceiling Decoration" for hugely overheating something or other and causing it to boil over enough to spray 10 feet up and onto the ceiling.

[Mosherette]

My A-level chemistry teacher was notorious for not using the fume cupboard properly. We got a day off college when he did this as he attempted to make aluminium chloride (by passing chlorine gas over heated aluminium). He was quite sloppy in other ways too, and this time not only did he not close the fume cupboard door properly, he also didn't check to make sure the seals on the chlorine gas canister were properly sealed. We left the lab pretty quickly.

[Troberg]

Originally Posted by KaiTheInvader

I had a chemistry teacher who would do an experiment every year, involving filling a pringles can about an inch full of rubbing alcohol, putting the lid on, and putting a lit match in a hole about 2" over the rubbing alcohol. It popped the lid off pretty high in the air and made a loud bang, and one student asked if he could do it with something bigger. So my teacher obliged, and this time used one of those large metal coffee cans. Only this time, not only did the top come off, the bottom came off as well, spilling flaming alcohol all over his desk!

Yikes, why so much? A few drops would be sufficient.

[Cestrian]

I'm sure health and safety must prevent such easy access to chemicals nowadays, but in my school days, every couple of months or so someone in class would make hydrogen sulphide and the lab would have to be cleared.

Then there was the student who added ascorbic acid to water, called it lemonade and drank it.