Exploring the Power of Steam
This is an article written years ago, but the message still resonates. Safety must come first!
A water heater exploded inside a restaurant in Southern California last year, killing one man, injuring several others and demolishing the rear of the building. Our purpose in writing about it a year later is not to second guess or affix blame. The precise cause or causes will probably never be known for certain. There is value, however, in looking at possible causes and contributing factors.
The water heater equipment at the El Torito restaurant was a fairly typical installation: a 726,000 BTU boiler, a ½ horse power pump and a 115 gallon, hot water storage tank. Water softening was provided by two adjacent tanks. Where are the potential weak points or trouble spots in such a set-up? We’ll explore several, some relating directly and others indirectly to the explosion.
One direct cause of the explosion was the lack of a temperature and pressure relief (T&P) valve on the storage tank, and a T&P is the last line of defense against overheating. When the system was installed six years earlier it is likely that a T&P was provided in the tank. For whatever reason, the T&P was plugged by the time the explosion occurred on August 1, 1993. You’ve seen leaky relief valves. It’s easy to imagine someone removed the annoyance from the tank, intending to replace it and then forgot about it. There was a pressure relief valve on the boiler, but that would not protect the tank from excess temperature as you’ll see.
One reason the tank explodes was that the water in the tank got too hot and there was no T&P relief. Now, how and why did the water get too hot?
We can deduce with some certainty that rusting was well under way inside the tank. First, the tank was six years old, and tanks which are not maintained, have generally begun to deteriorate by that time. (How many stories have you heard about five-year tanks giving out in five years and one day?) Second, this storage tank was fed with softened water. Since salt in softened water easily doubles or triples the consumption of a tank’s sacrificial anode, this tank had probably been without rust protection for several of its six years. (We’ve seen anodes completely consumed in as little as six months in over-softened water conditions.)
So the tank was most likely rusting away from both inside and out. Any number of conditions could have caused the weakened metal to fail--a restriction on the cold inlet, which blocked the expansion caused by heating, a water hammer caused by an automatic valve, or even a faucet closing. Fluctuation in line pressure could have done it. Or, if one too many molecules of steel rusted away, the bottom of the tank would begin to deform, cracking the already weakened metal and causing it to break. Once broken, a large leak would develop, instantly allowing the super-heated water to flash into steam with explosive results.
To get a clear picture of what happened to the tank at El Torito, you have to re-think your concept of water. Think of water as rocket fuel. And think of the steel tank, which holds the fuel as paper. With enough force, the tank will tear and wrinkle, just like paper does. Imagine that the static pressure involved here is 50 pounds per square inch (psi). The 18 inch diameter of the tank’s bottom has about 354 square inches, so that amounts to 12,700 pounds of pressure against the bottom… over six tons!
With a normal water leak, the pressure will drop as the leak grows, limiting the size of the tear. But with super-heated water/rocket fuel, the pressure will not fall off until much of the water turns to steam. The tank may already be through the roof by then! (Did you know a pound of steam is 1,700 times bigger than a pound of water?)
What ignited the rocket at El Torito? We imagine it was a combination of excessive rusting of the tank, some form of overpressure or water hammer and water which was heated over 212 degrees.
Whether or not incorrect equipment installation, improper equipment operation or equipment failure occurred is a moot point. It’s more productive to focus on the things which will make the system less dangerous.
It’s likely that people monkeyed with the controls, and not knowing all the effects of what they were doing led to an unsafe condition. To avoid this situation in your own work, talk to the people who actually use the equipment. Talk to the dishwasher. Is he satisfied with the hot water supply? Listen to any complaints or comments people have. Although they may not understand how the equipment functions, they know what it does or doesn’t do. Thy will give you the information you need to keep the equipment behaving, and that will help you to keep unskilled hands off the controls. Ask directly if anyone else adjusts or operates the equipment. Look for evidence of others’ work, like loose access covers, wrench marks or inappropriate settings. It’s not in anyone’s best interest to have unskilled hands on the equipment.
A comprehensive service routine and printed forms are needed to make sure regularly scheduled service/maintenance is adequate and complete. Mechanics may lose the ability to really see a system, especially one they’ve taken care of for a long time. Over familiarity can lead them to feel they know what components need maintenance, so some other parts may not be checked as well or as often as they should be.
It’s important to devise and use forms that require service and inspection information to be written down.
Keeping written records is still important even though we all use computers now. I like putting service info directly on the equipment, so it can’t be lost or ignored too easily.
I just finished teaching a class of about fifty maintenance people some of the nuances of water heater repair—and in the process I learned something about my source of strength.
We were playing with some dead water heaters that had been captured on their way to the dump. I like using old heaters as a teaching tool; they have stories to tell about their lives, if you know how to look. In that looking, we were removing pipe nipples from the tops of the heaters—and some were rather stuck.
A few students said, “This is too hard. I can’t do heater maintenance.” I don’t like the word “can’t,” so I jumped in to see if this old white-haired guy could make the stubborn pipe nipple move. I put my trusty Hoe Wrench from 1922 on the nipple and focused. The pipe came loose. Students were surprised!
It happened again twice. A student was unable to budge the pipe nipple (even using my wrench) and I waltzed in and made it spin. The young guys with visible muscles rippling in their arms had no success while the old guy did--what gives?
Finally, someone asked me what my trick was. I had to think for a bit, but I remembered back about forty years when I was shown this: Rest your hand on a friend’s shoulder. Have your friend put both hands on the inside of your elbow and try to bend your arm down. Resist by thinking about your arm and give it all the strength it has to stay straight. In my case, my arm bent despite my best effort. Now put your hand on your friend’s shoulder again, but this time concentrate on the area just under your breast bone as your source of strength and keep your arm straight. Let your friend try to bend your arm and see what happens. In my case, they couldn’t do it. My arm stayed straight!
I’m just a plumber, and I don’t know how this works, but I know it does. It turns out I’d worked this approach into my practice for decades without thinking about it. It’s simply that I refuse to walk away from a job without finishing it, and this “trick” has allowed me to finish every job. The guys who couldn’t make the pipes come loose thought I’d bested them, but really the point was that I’d demonstrated a tool we all have that most of us don’t use. It certainly sounds woo-woo, but with no doubt it works.
There are a couple of other not-so-obvious tricks I’ve learned over the years. For example, the plumber who appears to move the slowest often gets the work done the fastest. When you go to a job, sit down and map out the work in your head before picking up a tool. Understand every step of what you’ll be doing before you start. This way, when you get going on it, things will go together smoothly and you won’t need to re-work anything. When you finish, it will be just as you envisioned. That feels pretty good!
Here’s another trick that helps me work effectively. I’ve noticed that I think in pictures. When I can get a clear picture in my mind of what I’m trying to accomplish, it inevitably works. When I can only get a fuzzy image in my head, it doesn’t work; I wind up needing to figure out a different way. So, when you have the opportunity, see if getting a clear picture before you start works for you on your next project. It just might save you some time and frustration.
The moral of my story? Sometimes it’s the subtle shifts in focus that make your actions powerful.
Looking back over my working life of 50+ years, it seems clear that self sufficiency has always been the best way for me to be useful. Now, mix in a strong interest in water in its many forms and the wide world of animals and you'll know what's important to me.