CBS Sweeps Week Shocker: Glass Can Break!

Chicago’s CBS affiliate has discovered the laws of physics, and the shocking news is that…um… glass can break. Like, if you drop a dish made of glass it can… break (mechanical breakage), or if you put a very hot glass dish in cold water it can… break (thermal downshock).

In a segment blowing gale-force spin, CBS 2 tries to make out that a supposed spate of ‘exploding’ Pyrex dishes means that…um, glass bakeware isn’t safe. And if something isn’t perfectly safe, well, the question of where to apportion blame can’t be far behind.

“It may be the most popular glass bakeware in America,” said co-anchor Rob Johnson. “But tonight, some cooks are asking, ‘Is there a problem with Pyrex?” CBS investigative reporter Pam Zekman turned to one family for a shocking anecdote:

JULIA TUSO (Pyrex User’s Daughter): When it hitted (sic)
me in the hand I–I was crying. That’s why I said, ‘Mommy, I’m scared.’

ZEKMAN: Her mother had just taken a year-old Pyrex dish
out of a 350-degree oven. She put it on the oven door…

Ms. GINA TUSO (Pyrex User): .and when I turned back to
get a fork to flip the steak, I heard a loud explosion.

Mr. JOE TUSO (Pyrex User): There was glass scattered
everywhere, from 10 to 15 feet away from where it happened;
in three separate rooms.

ZEKMAN: Their daughter Julia was sitting across the room
at the kitchen table and was burned on her hand and neck by
a piece of flying glass.

First, glass doesn’t actually explode; it just sounds good for TV to say it does. It may sound like an explosion when it shatters (the sound is of atomic bonds being ripped apart), but there is no expulsion of gas, which is the signal for a true explosion. Glass can only be broken in tension, either by dropping it on a hard surface, hitting it with something, or subjecting it to dramatic changes in heat, which puts different areas of the glass in tension. So, for example, when a hot dish is placed on a cold surface or in cold water, the cooled surface shrinks in comparison to the glass inside, and the tension makes the glass break. Abrasions from, say, a chip or scoring a glass dish with a knife will exacerbate breakage.

So what actually happened in the Tuso’s kitchen? The only thing we know for sure is that the laws of physics weren’t broken along with the dish. It had to have been dropped, or have some prior damage, or have been exposed to extreme temperature change or some measure of all three. These are the only ways glass can break. But there are some real problems with the story – beginning with cooking a steak in an oven at 350 degrees and needing to flip it. Who bakes steak? Were the Tusos actually broiling the steak? If so, this is something Pyrex warns you not to do with glass bakeware.

It’s also hard, given that the dish apparently shattered on the door of the oven, to understand how the force projected upwards across the room to where their child was sitting, injuring her neck. The position of impact and the food in the dish would have directed the force outwards and downwards. Odd too is the fact the the shard of glass, apparently, retained enough heat after traveling a considerable distance and possessed enough sticking power to cause a burn.

[update - after reviewing the video, the wall oven appears high enough not to require upward force.]

But the questionable aspects of this kitchen misfortune raised no questions; instead, to make something more significant out of this misfortune, CBS 2 trawled a bunch of consumer websites for corroborating events in order to create the idea of an explosive trend – and it found some 300 incidents over the past five years.

But wait: Did CBS 2 verify that each of these events involved Pyrex? Did it check out the conditions in which the breakage occurred? Or did the reporters simply assume that an anecdote on a consumer website must be about Pyrex and must be a case of explosive shattering? No systematic analysis is presented by Zekman, so one can only conclude that they skipped checking the details out.

CBS 2 also cited the Consumer Product Safety Commission’s (CPSC) list of 66 complaints about for the last 10 years. That’s 6.6 complaints per year for 369 million Pyrex glass products manufactured since 1998 – assuming that the complaints did actually refer to Pyrex and not a rival glass product (once again, no-one checked). Add that number to Pyrex dishes still being used from before 1998, the overall rate of usage (say times per week), and one is left wondering: by what rational measure is this a problem worthy of headline treatment?

Based on emergency room data for 2005, you had a 1 in 3,706, 338 chance in the United States of sustaining a non-fatal injury from glass bakeware that didn’t shatter from mechanical breakage (i.e., being dropped). And even that is a crude estimation – a more accurate picture of the risk would involve the chance calculated per times glassware was used in cooking during the year, or per hour of cooking usage. For 2006 all calculation is moot: there were no injuries recorded by emergency rooms participating in the CPSC database, so the risk, as best we know, was zero. All of which means, compared to other kitchen equipment, glass bakeware is pretty darn safe. Take blenders for example, based on 2006 data, you have 1 in 95,152 risk for a non-fatal injury. And they have moving blades.

Because CBS 2 can’t figure out a way of explaining how Pyrex glass could defy physics and break in some special way that presents a hitherto unknown risk, the segment resorts to trying to show that the safety instructions are confusing to people whose Pyrex bakeware shattered (well, they think it was Pyrex, again no-one has checked). But the instructions explicitly warn about temperature changes and other conditions that can cause breakage and the overwhelming majority of people seem to be able to use their glass bakeware without mishap. CBS 2 promised a second segment tonight showing the results of its safety tests.

But if glass bakeware is going to be a benchmark for risk, and a handful of anecdotes the measure of a problem, people should stay out of the kitchen altogether. That’s where knives cut, and water boils, and things get hot. And, in fact, to be super-duper safe, people should probably avoid watching local TV news too, and not because it can damage your sanity, but because vastly more people injure themselves from television sets in the U.S. each year than from glass bakeware or blenders – in fact, based on 2006 data, you had a 1 in 5,613 chance of incurring a non-fatal injury from lifting, moving, and, believe it or not, watching TV.

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4 Responses to CBS Sweeps Week Shocker: Glass Can Break!

  1. [...] even though CBS failed to verify any of the anecdotes about exploding Pyrex (see yesterday’s post), and essentially relies on self-reported incidents from other Internet sites (since when is this a [...]

  2. [...] delivered part three of its investigation into “exploding” Pyrex last night (see here and here for reviews of parts one and [...]

  3. anon says:

    Actually, glass which fails from thermal shock does effectively explode under the stresses involved.

  4. Reader says:

    glass break no matter what

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