Posts Tagged ‘news’
Good Times, bad Times
June 22nd, 2010 at 6:29 am
The New York Times has a big article about the Deepwater Horizon, the failure of regulatory agencies to recognize and act on the hazards associated with offshore drilling, and—most interesting to me—the safety device known as the “blind shear ram” that was the last line of defense against a spill. When a newspaper covers an engineering matter, it’s usually hit and miss. In this case, there are hits, misses, and one curious omission.
First, the big hit. The “interactive graphic”—which is quite graphic, but isn’t interactive in the least—that accompanies the article seems really well done. I don’t know the details of the blind shear ram, but I’m familiar with similar hydraulic devices, and the drawings seem reasonably accurate.
Two large rams squeeze a set of pincers together, slicing and breaking through the walls of the pipe to close it off and prevent the pressurized oil below from escaping. If you’ve been trying without success to understand earlier verbal descriptions of the device, go to the graphics page and look at all the drawings and the animation. They should clear up the confusion.
The misses, though, are bothersome. First, a small mistake that seems to be the product of sloppiness. The Times says these devices are called blind shear rams “because they close off wells like a window blind.” This is nonsense. The action of a blind shear ram is nothing like that of a window blind. Window blinds rotate as you pull the control cord; there’s no rotation whatsoever in a blind shear ram.
I don’t have much experience with the oil industry, but I do with other industries that use piping, and the word “blind” is used to denote a dead end in a pipe—think “blind alley.” That’s exactly what the blind shear ram is supposed to do: create a dead end in the vertical pipe to prevent a blowout.
Now, I’m certain that the Times reporters didn’t make up this “window blind” thing on their own. They were probably told that the blind shear ram shuts off the flow of oil like a window blind shuts off the flow of sunlight into a room, and that’s why the word “blind” is in its name. But they screwed up the explanation, either because they didn’t care or because they don’t themselves understand how a window blind works.
A more important miss is in the title of the piece: “Regulators Failed to Address Risks in Oil Rig Fail-Safe Device.” The term “fail-safe” has a specific meaning, and it’s not a synonym for “backup” or “safety,” as the Times seems to think. Fail-safe is a type of failure in which the system stops working but goes to a safe state. It’s not simply an add-on device that works to mitigate a failure; it’s an integral part of a system’s design.
George Westinghouse’s air brake system for railcars is the canonical fail-safe design in mechanical engineering. Most pneumatic systems are actuated by raising the pressure. Through a clever set of valves and accumulators, Westinghouse’s design turns this on its head, actuating the brakes by lowering the pressure. This was a brilliant design decision, because the most common and important failures in a pneumatic system are hose and tubing damage, valve and coupling leaks, and inadvertent line separations, all of which lead to lowered line pressure. Westinghouse’s genius was to get all of these failures to apply the brakes, shifting the system to a safe state.
Westinghouse’s brakes were a safety revolution in the railroad industry and made him an incredibly wealthy man. The basic idea is still used today, nearly 150 years later.
Compare the Westinghouse brake to the blind shear ram. If the blind shear ram loses pressure, the pincers won’t move and the pipe will not be blocked off. Instead of moving to a safe state, the system doesn’t move at all, and because the blind shear ram is the last line of defense, the rig is now in the “you’re fucked” state. Which is exactly what happened to the Deepwater Horizon.
To be sure, the main theme of the Times article is that the blind shear ram is an inadequately tested and unreliable system. But the article gives the impression that if only the blind shear ram had a more reliable shuttle valve, or a backup shuttle valve, or if there were an entire backup blind shear ram, the rig would have had a fail-safe device.
It wouldn’t.
Making those changes might have made the blind shear ram a more reliable piece of equipment, and it might have prevented this tragedy, but it wouldn’t have made it fail-safe. In using that terminology, the Times is succumbing to marketing from the oil industry.
And with regard to the blind shear ram’s reliability, there’s this passage, which many readers probably questioned and which should have been explained better.
The benefit of two shear rams was examined last year in a report to Transocean. It estimated that while a blowout preventer with a single blind shear ram was 99 percent reliable, having two shear rams increased that reliability to 99.32 percent.
A reliability increase from 99% to 99.32% doesn’t seem like much, given that you’re doubling the number of blind shear rams. There had to have been plenty of readers scratching their heads at that, wondering why the second blind shear ram doesn’t do a better job of increasing the reliability. The article doesn’t address this question at all, but we can.
First, recognize that, according to this study, the second blind shear ram would reduce the probability of failure of the system by 32%, from odds of 100 in 10,000 to 68 in 10,000. Put this way, the second blind shear ram seems more valuable.
Still, the reduction in failure probability isn’t what we might expect from those old standbys of probability theory: flipping coins or tossing dice. For example, the chance of rolling a one with a single die is 1 in 6, or 16.67%. If we add a second die, the chance of both coming up one is 1 in 36, or just 2.78% Why can’t we use the same multiplication rule when calculating the effect of a second blind shear ram? Why doesn’t it work out to 1 in 10,000, or 0.01%?
The answer is that, unlike coin tosses and dice rolls, the failures of two blind shear rams would not be statistically independent. The conditions that lead to failure in one ram can lead to failure in the other. This is especially true if the two rams are made to the same design or by the same manufacturer. An explosion, for example, that damages one of the hydraulic systems has a good chance of damaging the other. To get statistical independence, you’d need a completely different type of device as the backup to the blind shear ram.
I know that by focusing on the misses and the omission, I’ve given an unfairly negative impression of the article. I don’t think it’s a bad article; I think it’s quite good, especially for a newspaper article written by and for non-experts.
But whenever I see mistakes on topics I know something about, I wonder if the article has even more mistakes on topics I know nothing about.
God as a thing
May 13th, 2010 at 10:29 pm
I was away from the internets yesterday and didn’t see this item until today:
A recording of a 1966 Beatles press conference at which John Lennon was quizzed over his controversial comments about Jesus is to be auctioned.
This is an August 17 press conference in Toronto, not the one in Chicago on August 11 that gave this blog its name. Let’s hear the clip from Chicago again:
As I’ve said before: poetry.
I was, frankly, sorry to read last month that the Vatican has forgiven the Beatles for this and their many, many other sins. The old boys just can’t seem to hold a grudge the way they used to.
No, you can’t click the links in the graphic: http://xrl.us/bhg7te, http://xrl.us/bhg7tg
Biking season is like deer season
May 4th, 2010 at 9:52 am
If you’re a bicyclist who rides in Naperville, you’ll be interested to know that the cost of attacking you with a car has just been set by a DuPage County judge: 21 days, to be served in three-day increments over seven weeks. And although the attacker has been forced to give up her gun owner’s ID card, she’s apparently still allowed to drive her weapon of choice.
I wrote a post about this story last year. In a nutshell: Two teenagers are riding their bikes in downtown Naperville. A woman driving near them gets pissed and stomps on the gas, aiming her car at one of them. The kid jumps off safely, but she nails his bike, which gets wedged into her bumper and undercarriage. She drives home, dragging the bike along. It’s still stuck to her car when the police arrive and arrest her.
Last week the woman, Mary Rehm, pled guilty to one charge of aggravated battery and was sentenced to 42 days, of which she’s expected to serve 21 in a series of three-day stints starting on May 10. So she’ll have a late spring filled with exotic three-day weekends in the pokey.1
From the article in the Naperville Sun:
Rehm, a gun owner, was also ordered to surrender her firearms owner’s identification card as a condition of the sentence, according to court records.
While it’s nice to see that this unstable idiot is having her gun owner’s ID taken away, I don’t see why she still has her driver’s license. Even during her “sentence,” she’ll still be able to drive the attempted murder weapon around the scene of the crime four days a week.
Liberal, socialist, communist, whitey-hater that I am, I can’t help but think that had her name been Maria Ramirez rather than Mary Rehm, she wouldn’t have gotten off so lightly.
Be that as it may, cyclists should know how much DuPage County values them. Drivers should know it, too. Hate those cyclists who take up space on your roads? Got some vacation days coming? Tune up your engines and come to Naperville!
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“Pokey” was one of my grandfather’s favorite words, and I seldom get a chance to use it. ↩
Scratch off
April 21st, 2010 at 11:35 am
This NY Times article about banning an app from the App Store is really poorly written and jumbles up a couple of related, but distinctly different, aspects of iPhone OS development.
The main topic is Apple’s recent decision to remove the Scratch Viewer app from the App Store. Scratch is a teaching language/environment from the MIT Media Lab that’s intended to help kids learn to program. It seems to be a followup to Squeak, which was, in turn, a followup to Smalltalk. Scratch Viewer was an app that ran Scratch programs. According to the Times
Scratch Viewer was designed to let educators and others review a child’s work that was created on an iPad, iPhone or iPod Touch using the Scratch programming language, which has become popular in many schools.
I think the “created on an iPad, iPhone or iPod Touch” part is wrong. Everything I’ve read about Scratch Viewer indicates that it was, as its name implies, an app for viewing, not creating. If I’m right about that, the educational value of Scratch Viewer is not as great as the Times suggests.
(I’m going to confess here that I’m dubious of the educational value of Scratch itself, let alone Scratch Viewer. Alan Kay has been trying to push various forms of Smalltalk for decades and it just hasn’t taken off. The ideas of Smalltalk are everywhere, and he’s a tremendously influential figure because of that. But Smalltalk itself just isn’t a language most programmers enjoy using, and there’s no evidence that exposing kids to Scratch will change that.)
Whether Scratch Viewer allowed programming or not, Gruber was exactly right: “It’s only surprising that it ever made it into the App Store in the first place.” Apps that include code interpreters have always been disallowed.1 And this is where the Times jumbles the story.
This paragraph about halfway through the article is the problem:
But bloggers are theorizing that Apple removed the viewer because it violates Section 3.3.1 of the company’s policy against apps that interpret or execute code. This is the same reason that Adobe Flash-based apps are not permitted, as covered in this Bits blog post by Nick Bilton.
The linked post is all about the recent changes to Section 3.3.1 that killed Adobe’s Flash authoring tool in Creative Suite 5. The idea behind CS5 was to allow developers to write programs in Flash and compile them into executable apps for the iPhone. It had nothing to do with installing a Flash interpreter that could run any SWF file.2
By bringing up the changes to Section 3.3.1, the Times is saying that Apple screwed Scratch Viewer by changing the rules in the middle of the game. This is simply not true. You may not like Apple’s “no interpreters” rule—I don’t—but it’s been absolutely clear since the App Store opened, and Scratch Viewer has always been in violation of it.
Thanks to Tom Levenson for tweeting a link to the article.
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Not that other interpreters haven’t slipped in. This HP 15C emulator is a programmable calculator app and must have a built-in interpreter. I doubt it’s using JavaScript. ↩
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To be sure, apps compiled with CS5 may well have a small bytecode interpreter embedded in them, but that interpreter is only for the code in the app itself. It’s not a Flash Player app. ↩
Playstation 3 leap year bug
March 1st, 2010 at 9:46 pm
As a big fan of Reingold & Dershowitz’s Calendrical Calculations, I’m always on the lookout for calendar-related programming news. This morning I heard (via @jamesthomson) that the Playstation 3 has a leap year bug that screwed up a lot of users yesterday when it became midnight GMT and the calendar flipped from February 28 to March 1.
In addition to my nerdy calendar interest, there was a family angle. My son plays Modern Warfare online with many of his friends. Last night he told me that a few of them were locked out because they couldn’t get online. It seemed weird that 3-4 kids would have network problems simultaneously, but now we know it wasn’t a coincidence.
Unless there’s a leak out of Sony, we may never learn the precise cause of the bug, but it must have acutely embarrassing for an international electronics giant to have to post this:
We are aware that the internal clock functionality in the PS3 units other than the slim model, recognized the year 2010 as a leap year.
Let’s first note that recognized is the wrong verb; you wouldn’t say you saw Ernest Borgnine in a restaurant and recognized him as Brad Pitt. How about mistook? More to the point: can you imagine spending millions of dollars to develop a product that can’t figure out whether a given year is a leap year or not?
My guess is that the firmware takes every even-numbered year to be a leap year. The PS3 came out in late 2006, too late for the bug to have an affect that year. 2008 was, of course, a real leap year, so the faulty code worked. Yesterday was the first time in the PS3’s product life that the bug would cause a problem.
I’m pretty sure that Sony has no real fix. The solution, like Microsoft’s solution for the Zune’s leap year bug back in 2008,1 was to simply wait until the calendar flipped again. Now that February 29 March 1 is over in the GMT zone, the bug is safely tucked away. If my guess is right, it won’t resurface until 2014, by which time most “fat” PS3s will be out of service.
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Yes, that was a self-link. I’m positioning myself as the go-to blogger on leap year bugs. ↩
Chile’s earthquake
February 27th, 2010 at 9:59 pm
I’m not surprised that—so far, at least—the death toll from Chile’s earthquake is so low compared to Haiti’s, despite the much stronger quake. I was trained as a structural engineer, and my department was loaded with graduate students from South America. Latin American countries tend to take earthquakes very seriously, and their engineers are highly educated, both at home and abroad.
News reports will, of course, focus on the devastated areas, but most of the buildings must have done an excellent job of protecting the people within. This is not to say that the buildings weren’t damaged; there’s too much energy in a big quake to expect most buildings to escape unscathed. But I would expect to see most engineered buildings1 to have absorbed the energy without large-scale collapse.
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Buildings that were designed by engineers, like office and apartment buildings. Older, smaller residences are typically not engineered and usually suffer the most damage. ↩