The Straight Dope®
I work for an electric utility. I've heard tales over the years of invisible high-pressure steam leaks in power plants that have "cut people in two." Any truth to this? --wr99gre, via email
Much to the disappointment of my inner ghoul, so far I've turned up no confirmed cases of steam bisection. Could it happen, though? You bet.
The boilers in a typical power plant generate steam at around 2,400 pounds per square inch--about 163 times atmospheric pressure. Some "supercritical" steam plants operate at pressures over 4,000 PSI. Here the steam is heated far above the boiling point, generally to 1,000 degrees Fahrenheit or higher. This "superheated steam" is invisible when released until it starts to condense back into liquid water. Combine high pressure with high temperature and a jet of steam from a leak could travel a long way before becoming visible to an unwary passerby. Anyone walking into such a leak would be seriously injured or killed by the heat alone.
It's been well documented that jets of high-pressure gas (which is what superheated steam is) can cause injuries even without the added complication of heat. OSHA warns against possible amputation from high-pressure gas and limits air pressure for industrial cleaning to 30 PSI. High-pressure gases can easily penetrate the skin, especially via an existing cut or wound, and potentially lead to gas embolism--bubbles in the bloodstream that can migrate to the heart, lungs, or brain and cause serious trouble. U.S. Army medical reports tell of numerous gas-penetration injuries suffered during training with blank firearm rounds. Just 12 PSI can likely pop your eyeball from its socket. Less than 80 PSI of air from 12 inches away reportedly swelled up a woodworker's hand "to the size of a grapefruit." One source reports that high-pressure nitrogen cut into a worker's leg like a knife, and other references warn that high-pressure gases can cut fingers, toes, and other body parts. Again, I didn't find an actual case of high-pressure gas cutting anyone in half, but its not going out on much of a limb to say it sure would smart.
Steam leaks can injure or kill in many ways. The force of a high-pressure leak, for instance, can turn loose items nearby into projectiles. My assistant Una, who works in the power industry and has visited more than half the steam power plants in the United States, once witnessed a rupture in some 2400-PSI steam pipes that flung a set of heavy welding tanks 50 feet and through a sheet-metal barrier. Pieces of pipe, insulation, tools--almost anything can become deadly in such circumstances. Ducking won't necessarily save you--a big steam leak in close quarters can quickly raise the surrounding air temperature so high youll cook from the inside if you breathe. Even at lower temperatures enough steam in a small area can suffocate you as it displaces the air. Una has a friend who got nicknamed "the Lobster" after a relatively low-temperature steam accident--he was exposed to a wet 180-degree leak for a few seconds and spent nearly a month in the hospital. An indirect low-temperature leak can also lead to heat exhaustion if youre around it long enough.
Its common belief among utility operators that a good way to check for high-pressure steam leaks is by waving a broomstick in front of you: when the stick suddenly gets chopped in half, you've found your leak. However, Una contacted operations personnel at several power plants across the United States, and while almost all had heard of this alleged practice, most thought it would be an unusual way to find a leak these days. A leak in a steam line with enough pressure to cut a broom in half would likely warrant shutting down the unit. Given the danger of a fatal mistake, it's hard to imagine a plant boss sending workers out on a search mission armed only with a trusty broom. Una further points out that a steam leak, invisible or not, usually isn't tough to locate--imagine a locomotive horn a few inches from your ear. Operators in an enclosed control room can hear steam leaks from several floors away.
Some industry sources speculate that using a broom to search for leaks may have started aboard ships with steam boilers, where tight quarters and noisy conditions may have made it difficult to find leaks quickly without some direct evidence. It may even have been recommended as a way to survive a steam leak, using the broom to check that the route to safety was clear. Then again, most shipboard steam isn't at high enough pressure to slice through wood (although it could cut the bristles). Personally I'm guessing the broomstick thing is part of the informal neophyte training process familiar to anyone who's worked in industry: "Did they tell you about high-pressure steam leaks? Cut you right in half. Better wave this broom."
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