Aftermath photos of residential boiler explosion-no relief valve

Constantin

... as little as I know about steam systems, being a mere homeowner and all that.

I suspect the unit was dry firing because of a nonexistent LWCO. Then, when it was nice and hot (i.e. cherry red) a slug of water hit the boiler. The T&P either is nonexistent, clogged, or nonfunctional. Everything goes to hell in a handbasket as the steam pressure builds and the boiler then explodes.

I'll be interested to hear what you guys found. Hopefully, nobody died like in many of Dan's stories. Too often it seems, someone in charge of the boiler gets killed for trying to add water to a boiler that had been allowed to run dry.

Mark Woll_2

Thought boiler exposions were a thing of the past?

Here's one I worked on for 3 insurance companies, one for the house at the site of the explosion, plus the neighbors on each side.

Look at the pictures, tell me what you think, then I'll let you know what apparently happened (as much as we could piece together!).

Ken D.

Explosion

I witnessed the aftermath of a similar situation about 10 years ago. It was at a neighbor's house of our customer. It was a rowhouse with 1 1/2 foot thick stone walls. The gas water heater was just inside the back door. The thermostat failed and the heater ran away. The pressure built up because the relief valve was blocked with crud. The heater took off like a rocket through the front stone wall, across 4 lanes of traffic, through the front upstairs wall of a house across the street coming to rest in the bathroom in the middle of the house. I have always checked relief valve operation to be sure they will relieve on every inspection, cleaning and sevice call. I have had to replace many a valve because it would leak after checking and had many a P.O.'ed customer, but it is not worth the chance of an accident. I have also discovered many a blocked relief valve during an inspection, avoiding a potential disaster. It is amazing how much power is in one of those things. You can't be too careful.

Unknown

not even close

If it were a steam system, there wouldn't be a hot water system hanging from the joists.

Steam is compressable. A slug of water wouldn't build pressure so much as the thermal shock would crack the boiler and release the now superheated water. No evidence of that here.

This was an overpressurized water boiler.

Mike T., Swampeast MO

One of those old "auto-manual" gas valves malfunctioned or was accidentally set to "manual"? Relief valve removed because it had started to leak?

Joe_50

explosion

I see the oil tank in the basement. Was there natural gas in the home?
In the past 10 or 15 years I can recall 3 properties having gas leaks in their basements causing an explosion in my area. 2 of them were stick built homes that leveled them in a heap and the third was a brick and stone building that did a massive amount of structural damage that they brought in equiptment and took it down.

Speaking of relief valvles I was to a Labor and Industry seminar and they showed a film (I think it was from watts) of what happens with water heaters with no reliefs. They had these heaters in the middle of a field and plugged them up and ran them until they took off like a rocket and went hundreds of feet in the air. Also showed us pictures of a well-x-trol tank that didnt have a relief on it and apparently the pressure switch stuck causing that to go launching up through the 2x10 floor joists of a resturant.

Mark Woll_2

Not a gas leak, it was a hot water oilburner--more details!

The heating equipment was a very, very old TIMKEN rotary boiler converted at sometime in the past to a gun type high pressure oil burner. It was fitted with a tankless coil directly above the boiler.

The as the unit exploded it launched upwards into the living room. (look at the dirty water residue in the living room photo). Luckily this house had massive 3x8 floor joists typical in row houses of this age that acted as a cage I guess because all the boiler parts were still in the basement. However a huge instant pressure-pulse from the explosion destroyed the house's masonary like a bomb.

We searched forever for every inch of heating equipment as if we were reconstructing a jetliner crash. We found everything and every pipe. We reconstructed it in a rented u-store it locker. We accounted for every connection.

The original Timken had a COMBINED automatic water feeder AND pressure relief, an old B&G Dual Eight, however, we found a rather brand new FB-38 (no pressure relief) had been installed by an oil company just a few weeks prior.

For an undetermined reason the boiler's operation during a call for heat by the thermostat was not interrupted by the high limit switch Honeywell pipe surface mounted aquastat installed. Perhaps it had little or no water to activate the aquastat, perhaps the oil company forgot to fill it, perhaps the fill valve opened to a dry boiler, we'll never know.

The actual explosion occured in the overhead tankless coil, the weakest link, which probably saved the owner who was on the couch right in the living room when the explosion occured.

Interestingly, both their cars were destroyed too; one was parked in the front, one in the back!

Constantin

My favorite description of a FMEA analysis

was in "why buildings fall down". A fantastic book.

A new york skyscraper was leveled because a water heater T&P had been plugged. When the water heater took off (one of four, the second one on the same system was about to blow) it hit a 4" gas main.

The gas main promptly fell apart because it had been engaged with only 2 screw threads (!!!). The building then filled up with gas, particularly due to the elevators pumping the stuff up and down the shafts until they went stoichometric and WABOOM!

Luckily, this happened at 6 AM or so, before the building was filled with a lot of people. Unfortunately, that didn't help the few that were in the building.

Anyway, the damage makes me wonder if the place didn't have two explosions. One of the boiler, and another one of gas. However, there is no fire damage that is readily visible... so I guess I have to discount that possibility.

Tony Conner

There Have Been...

...SPECTACULAR boiler explosions from adding water to a hot steam (or hot water) boiler with no water in it. The first reaction most people have to seeing no water in the gauge glass of a firing steam boiler is to get water into it. That is an EXTREMELY dangerous thing to do, unless you were standing right there when the water dipped out of the bottom of the glass. Sometimes, nothing particularly bad will happen when water is added. Other times, the boiler will be damaged. Other times again, a slug of cold water (and I mean relatively cold - it could be condensate temperature - it doesn't have to be tap water temp) into a dry-firing boiler will cause catastrophic failure. If you're "lucky", it'll leave the building as pretty much one lump of high velocity metal, and most of the structure will remain pretty much intact, like in the pictures. A lot of expensive damage to repair, but people can exit the building. The other possiblity is that it will become more of a bomb than a missle. Whole buildings have been leveled in events like that.

A lot of people will see these pictures, and get freaked-out over steam or hot water boilers. They really shouldn't. A properly installed and maintained boiler, and the fuel source that fires it, is no more dangerous than the electrical power that is in every room in your house. Many of the same folks who will worry about their boilers now, will routinely do just TERRIBLE things casually storing & handling the gasoline for their lawnmowers, snowblowers and boat motors. They'll worry about how dangerous boilers are, while calmly looking for the side-cutters so they can cut the ground pin off an electrical extension cord. All energy sources should be respected. If they've got enough power to do any amount of useful work, they've got enough power to kill you, under the right circumstances.

Steve_57

I've found many inaccurate aquastats on boilers, the most severe was off by 80 degrees. A tech went to a customers house and adjusted the aquastat to 180-200. When I got there the boiler was at nearly 300 degrees with steam coming out the high vents and the boiler actually shaking from the pressure.

Mijola

Mark

I have a question that I do not want to post on the board. I tried to e-mailyou directly but it would not got through on the e-mail address on you post.

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Fill in the spaces between the letters in my e-mail address below. No caps, no spaces. Sorry to be a PIA but I do this to try and fool the spam bots.


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Mark Woll_2

The aquastat dial was set for 180 F,but it was mostly destroyed

It could not be throughly tested.

Mark Woll_2

I agree with you, Ken

Our physicst gave the opinion that even a relatively small psi pressure-pulse exerted over a large area, especially on a surface which is unyielding such as stone can inflict catastrauphic failures.

Mark Woll_2

I actually have the sister book, Why Buildings Stand Up

It was written by a Mario somebody if I recall

Mark Eatherton1

The power of water and fire...

are AWESOME...

I'm glad there were survivors. They're not usually that lucky.

ME

Dave McGavin

High Limit switches are only as good as wiring to the burner!

External safety controls that open an electrical circuit in case of excessive temperature or pressure should be wired as though lives depend on the integrity of the insulated conductors. Wire or cable "draped" from a safety control to the equipment being controled can get pinched or melted on hot surfaces. The high limit would be effectively by-passed as a result of a short circuit in the vital safety circuit. That old Honeywell high limit could have performed flawlessly but careless wiring can negate the best safety control.

I think we need to emphasise better installation practices and the difference between safety wiring and operating controls. The wires going to a safety control must be installed so that they are immune to rodents chewing the insulation or a sloppy service person. Thermostat cable (LVT) is often used for safety wiring even though it is a soft, low temperature control cable suited to - thermostats. I would like to see safety wiring to "remote limits" protected by flex (conduit) or armoured cable to prevent more tragedies.

Mark Woll_2

Dave raises an awesome point!

You are absolutely correct! And we never thought of that!
(incidentally this explosion is a long closed file of many many years ago)
But who doesn't see it time and time again! Of course what are you supposed to do when you come across someone else's crappy work? Rewire it? Hang it out of harm's way? Maybe yes. Certainly the installer here had a duty to fit a pressure relief valve, and then the question arises, did the later service technician that week have a duty to notice the missing relief valve? If he did, did he have an obligation to do something about it? If so, what? Hmmmmm......

I would suggest that written notification to the owner specifically identifying problem areas such as inadequate wiring is a mandatory item. The owner should sign.

But a dramatically life-threatening omission of a relief valve, if noticed by a technician, he probably should shut the system down pending correction. But what if it's the dead of winter? What if the owner doesn't want him to shut it down, nor fix it????????? hmmmmmm.....

Mark Eatherton1

I was always taught...

that you should run the hot (in the case of 120 volts) or the R leg of a 24 volt transfor through the safeties. This way, if it DOES short to ground, it should either take out a fuse, a circuit breaker or at least the transformer.

Is this not considered an industry practice??

ME

Kyle Kubs - Benchmark Home Inspections

Good Post

Mark, any chance you could e-mail me these pictures in a slightly larger resolution/size - With your permision I would love to use them as part of my educational materials - All to often I run into a know it all home owner or real estate agent that thinks a malfunctioning PRV or T&P is a minor issue or that it can be capped till someone can get by to fix it.... I tell them the facts and the usuall stories, but as they say these pics are worth many thousands of words. If you can please send them to me at kyle.kubs@nospambenchmarkinspect.com (just remove the nospam from the address...) Thanks, Kyle

Kyle Kubs - Benchmark Home Inspections

Good Post

Mark, any chance you could e-mail me these pictures in a slightly larger resolution/size - With your permision I would love to use them as part of my educational materials - All to often I run into a know it all home owner or real estate agent that thinks a malfunctioning PRV or T&P is a minor issue or that it can be capped till someone can get by to fix it.... I tell them the facts and the usuall stories, but as they say these pics are worth many thousands of words. If you can, please send them to me at kyle.kubs@nospambenchmarkinspect.com (just remove the nospam from the address...) Thanks, Kyle