safe distance from a steam pipe that ruptures 7

[ss123]

In light of the recent fatalities at the japenese nuclear plant caused by the rupture of high pressure steam pipe which caused fatal burns, could someone tell me how I could estimate what safe distance a person needs to be away from the pipe in case of rupture.

My steam pipes carry 10barg saturated steam. I've been told that a temperature of 70C is sufficient to cause fatal burns.

 

[Latexman]

In above post, ? = Integral sign.

Good luck,
Latexman

 

[sailoday28]

Latexman
If we consider the downstream volume to be extremely large, the internal energy analogy that I suggested should still work. For smaller volumes with relief openings, we would have to consider a mass energy anlysis for the downsteam room. And that can be a messy analysis.
Regards
sailoday28

 

[CHD01]

Refer to API 521, Section 4; you may also want to look at its appendixes. Note that inclusion of referenced formulas depends on the version of API that you have, it may not be in some of the later versions.

The more you learn, the less you are certain of.

 

[4Pipes]

See the link to the Iwo Jima valve failure. A case of not following the rules.

http://www.nationalboard.org/nationalboard/articles/classics/classic57.aspx

 

[hacksaw]

Briefly served on the Iwo Jima in the 60's. It was a converted WWII aircraft carrier and used for vertical assaults and for retrieving astronauts from the Pacific. It was decommisioned shortly after this failure ('97).

 

[rmw]

Interesting read. Back to ss123's original question. Looks like there was no part of that boiler room that was safe in this incident. I wonder if any of them even tried to get into the bilges. (see my post of Aug 12 to understand this last comment.)

rmw

 

[saxon]

Classic case of SNAFU. I'm surprised we don't have more disasters. A bolt is a bolt, a stud is a stud, a nut is a nut and parts is parts. Right?

One question, where was the officer in charge of repairs?

saxon

 

[rmw]

Hacksaw,

The DDG I served on in the 60's, the USS Conyngham, DDG-16 was scrapped shortly after a fwd fire room fire caused by an exploding fuel oil pump back in the '90's as I remember it.

Strange, this was one of the first series of ships in the USN that was 1,200 PSI steam, and the older hands (I was green) who had worked with 600 PSI steam for lots of years were scared to death of it.

But that, in the end, was not what got this ship.

I worked on that firing aisle where the pump failed. Eirie when I think about it.

rmw

 

[hacksaw]

pays to be a little scared with steam

 

[pandora]

LuizSouza,

The author of the book in question is Trevor Kletz. He has also produced many other great safety books.

Hacksaw is right, it pays to be a little scared of steam, because one thing Trevor Kletz points out in an early book is that the single most dangerous chemical we use is nitrogen, you know that big part of the air we breath. We get so complacent about using for inerting flammable atmospheres that we forget it kills.

 

[Wilkie]

You have received some very good responses here. I am a little late in replying to your post, but have nearly 30 years experience in the chemical industry and as many of the other post contributors here, have experienced the hazards of steam firsthand.

Things that CANNOT be over-emphasized are:
- Assure yourself that your system is adequately designed and is OPERATED ACCORDINGLY. I use "adequate design" as an all-inclusive term which includes proper engineering of your system, correct materials used in construction, appropriate construction procedures used, proper gaskets, etc. In regard to protecting personnel from ruptured steam pipes, it is much better to PREVENT an occurrence from happening in the first place.
Seemingly minor components such as pipe supports or gasket thickness can play a significant role in overall system integrity (or failure) under the right circumstances.
With all of the downsizing and staffing cutbacks it is becoming much easier for a system to be operated outside of its' design limits and going unnoticed, until problems develop. Computerized control systems often help by notifying personnel when safe operating parameters are exceeded, but only when the warning is heeded and acted upon.

- The response about the aging workforce and long hours is right on the money. I was seriously burned years ago (and I wasn't THAT old at the time either) when a steam hose ruptured under 200 psig pressure. I was only six inches away when it blew, and it removed almost two square feet of skin from my stomach and back. I was working a double shift, was tired, normally wouldn't have had my body in the awkward position that it was, and most likely would have noticed signs that indicated the hose needed to be replaced before I used it.

- Don't ignore seemingly impossible (or highly improbable) events. In cold weather, a failed steam trap in the right place can result in pipe fittings freezing, which can crack and then burst when the weather warms and the line thaws out. I have actually watched a 20-foot section of pipe "unscrew itself" and blow off - carrying many yards away - when a elbow fitting on one end froze and then burst when it thawed out while the rest of the line was still under steam pressure.

Good engineering should not only consider the overall purpose and design of a system, it should also include the potential for operational upsets, equipment failures, and human error / stupid acts in general. You cannot design for all possible "stupid acts", but you CAN decrease the risk if you are aware of some of the things to lookout for while a project is still in the design stage. Things you can't design around should be taken care of administratively or with personnel training. The previous post regarding restricted access to operating areas is something my plant also practices, and is a highly recommended method to minimize unnecessary risk in industrial facilities.

Steve

 

[JStephen]

Maybe I'm missing something here. If you have a reasonably large steam line exhausting into the atmosphere, you would get a large cloud of steam at that point. If, as in the Iwo Jima example above, that line is connected to a sizable source of steam, you could conceivably have a large cloud of hot steam drifting hundreds of yards from the source, and still being dangerous. That steam does not cease being dangerous just because it is no longer part of a "jet" being emitted from the pipe.

I can just visualize the situation where a steam line is in obvious distress, with a crowd of spectators standing behind the "Safe" line painted on the floor, to watch it blow....

 

[TBP]

As the steam jet contacts atmospheric air, it mixes with it, and cools fairly quickly - as long as there's enough air and/or a small enough leak. I've also seen several "interesting" water hammer events, and can't recall a crowd gathering. Typically everyone in the area is very much aware that something potentially bad is unfolding, and can't wait to put a significant amount of distance between themselves, and the line or equipment in question.

 

[JStephen]

I was just kidding about the spectators, TBP, but you illustrate the point I was getting at- there's not a "safe" distance, other than the next county. "If there's enough air and a small enough leak" are two factors that aren't stated in the question, which means there's really no way to determine a safe distance.

The problem strikes me as similar to the gas releases at the chemical plants. They don't try to tell you "this far is safe". You just evacuate cross wind and hope for the best. In this case, the risk is thermal rather than toxic, but the same issues arise.

The original statement says a temperature of 70 degrees can cause fatal burns, but that doesn't mean 69 is safe- so the criteria for safety is open as well.

Depending on the nature of the leak, you could have flying shrapnel as well. I remember reading of an intentional head-on locomotive collision quite a few years back, and as I recall, the damage was done by flying parts and not by steam (didn't help that the locomotives were riveted).

 

[steveen]

For what it is worth.
During world war 2, there were many fatalities aboard ships due to high pressure steam leaks. One problem with high pressure steam is that, besides the noise, there is no way to see the plume.

Many fatalities occured by people walking through the enginer rooms -- during action -- and literally getting cut by the high pressure steam leak. One of my seabee buddies, tells of using broom sticks to check for high pressure leaks, if the handle fell off, you found one.

Training of personnel around high pressure steam systems is recommended. Planning to have flanges located away from areas of personnel is difficult, but can be done.

 

[25362]

Pay a visit to:

http://www.kirsner.org/pages/articlesAlt.html

Mr Kirsner analyses steam burns, and other factors that may be relevant to this thread, in the article titled: Surviving a Steam Rupture....

 

[FredRosse]

A steam jet discharging to atmosphere typically becomes an eductor, and entrains a large amount of ambient air, cooling the bulk flow considerably. This phenomenon is strongly influenced by The safe distance depends on the size of the steam pipe rupture, pressure, etc., and the surrounding enclosure.

For example, a small "Try Cock" on a 10 bar boiler is opened to test the water level in the boiler. By passing your finger near the jet issuing from the Try Cock, the operator detects if steam (feels cool) or saturated water (feels hot) is on the other side of the Try Cock. I have done this hundreds of times.

A small "rupture" of this size is normally harmless at 1 meter distance, but could cause problems if continuously discharging into a relatively confined space which would heat up to greater than 70C in a short time.
the local geometry. Flashing steam/water mixtures are worse than pure steam, and have a greater potential for personnel injury in many situations.