I drive by rural operation that receives train cars of propane. I tried reading up on the process but I’m still unclear on some of it. It comes out of a pipeline as a gas and turns into a liquid when pumped into a car under pressure? Why are some propane cars white and others black? What happens if there is a leak? Isn’t that car a rolling timebomb?
While it is a gas at room temperature and atmospheric pressure propane does not require massive pressure to be compressed into a liquid, 177 PSI will do it at 100 F. This means that tanks capable of containing liquified propane can be constructed relatively easily. For comparison, even at over 3,000 PSI natural gas is still a gas, and it requires much stronger (heavier and expensive) tanks to hold it. Cooling the gas makes it liquify at a lower pressure, but then you have the expense and complexity of the refrigeration system.
When stored in tanks or railcars and at loading/unloading facilities propane is kept as a liquid. When delivered by truck and stored in tanks at the end user’s facility it is kept as a liquid. It is only allowed to expand into a gas when it flows through the regulating valve out of the tank, heading to whatever appliance will burn it.
Some locations have large underground caverns (usually left over from salt mining) that are used to store propane or other gases. Here’s one from my area:
A propane leak is similar to a natural gas leak, but the main difference is that propane is heavier than air (natural gas is lighter and floats away) so it will accumulate in underground spaces. That is why propane powered vehicles are not allowed in underground parkades. If either kind of gas leak encounters a ignition source watch out!
Any tank car of combustible gas or liquid is a rolling time bomb if the right conditions are met, but propane is more dangerous because it will boil and expand into gas at a much lower temperature than gasoline or other fuels. You have probably heard the term BLEVE before (boiling liquid expanding vapour explosion). This is where a intact tank
With a BLEVE, not only is there a fireball, but sometimes part of the tank can become a rocket. Not quite into orbit, of course, but parts could travel a quarter mile and more in the wrong circumstances. In recent decades various design modifications have been made to the tankcars to make BLEVEs even less likely.
After a couple of major disasters involving LP cars (Oneonta, Kingman, to name two) there were changes, although I’m no expert on what they did.
As I learned it, when a tank fails, one end will rupture and lay out open while the other end remains intact - a cylinder with a closed end - and becomes something of a rocket. I’ve heard reports of the railcars traveling 3000’ and more.
One thing (probably the main thing) that causes the tanks to fail is direct flame impingment. A double shell can help prevent that, and I think that has been the “cure” for rail cars.
I did once see a report from a fellow who got caught inside a BLEVE of a local distributor-type tank. He wasn’t hit by any debris, and suffered no significant injuries, but did relate that the burning droplets made an interesting “rain of fire.”
A fire involving a large LP tank is one of those situation where we invoke the “rule of thumb” - if your thumb, held up between you and the incident, you’re far enough away.
So it’s stored in a liquid state because it’s under pressure? What happens if there is some sort of small leak out of a tank? Does it turn to a gas as it excapes?
Tree- you’ve probably seen this: about every other year a house in the rural areas or small towns around here suddenly turns itself into a pile of toothpicks when the propane decides to get cranky.
If a RR takes this on it should be with a CYA that avoids litigation and criminal penalties. Why take such risks unless required to do so by federal common carrier requirements.
Happened last year in Massachussetts with an overpressured natural gas line. Quite a few houses succombed, keeping area fire departments very busy in three cities (with a lot of mutual aid) outside Boston.
Switchmen still refer to the things as “Bomb Cars”, especially the 4-trucked behemoths. Diningcar and I both worked with folks that were there at Kingman. The image of rail melting under the wheels of the railcars and the stories about scrambling around to minimize the end result will always stick with me. Fortunately I was 7 years or so from hiring-on.
The railcar is no more a rolling time-bomb than the pipeline is a potential industrial flamethrower. (Ask PG&E in the bay area)
Going on in the courts and the STB still.
Pipeline Natural Gas is mainly Methane (CH4) with varying small amounts of Ethane(C2H6). Propane(C3H8) is the next heavier Hydrocarbon above Ethane. Next are Butane, and then Pentane. After Pentane is Hexane, the most important component of the Gasoline you put in your car’s gas tank, In winter small amounts of Pentane are added to Gasoline to help it vaporize in cold weather
Murphy,
I never figured you for a chicken little kind of guy. I worked for the Bureau of Explosives for 5 years and SP Hazardous Material Control Department for 8, so propane in tank cars is something I KNOW about.
Propane is a straight chain hydrocarbon as Beauleau described. It can be liquefied at relatively low pressures, how low depends on the temperature, and there are vapor pressure/temperature charts that let you determine pressure or temperature if you know one but not the other. About 90% of the tank is liquid and 10% vapor in round numbers. It takes a page of calculations to figure out how full to fill each car based on the temperature of the product being loaded. If the lading is 55 degrees F, then pressure is 100 PSI gauge. At a temperature of 115 F, pressure is 220 PSI gauge.
Propane was first shipped in ICC specification 105A300W tank cars, which are insulated cars. In the late 1950’s the 112A340W uninsulated car was introduced. The top 2/3 was required to be painted white. The general rule about safety valves is that they start to discharge at 75% of the tank test pressure, that is 225# for the 300 pound hydrotest insulated car, but for the 112 cars the specification allowed STD of 82.5%, a 10% bump, which is 280.5 pounds for the 112A340W car. Since the cars are/were not insulated, the reference temperature was 115 degrees. Since pressure at 115 degrees will be 220 pounds there is a 60.5 degree spread between maximum expected pressure in transportation and the start to discharge pressure. All is well.
You asked about leaks. Leaks will always involve the fittings. A loose plug at liquid or vapor or slip tube, or a loose valve attachment to the cover plate for example. Most of these will be vapor and so minor that they can not be detected from the ground and vapors will be rapidly dispersed and thus present no threat to anybody.
Liquid leaks are more worrysome since one volume of liquid will convert to 280 volumes of vapor. If you see frost running down
There is a significant difference. If a small leak emanates from a tankcar it usually dissipates into the surrounding atmosphere. Inside a house, on the other hand, it can collect and increase in concentration (especially in a basement)until the atmosphere is an explosive mixture waiting for a spark.
The one additional factor to bear in mind is that if it is a very calm day, gases that are heavier than air may collect in a surrounding low area. (Others have already mentioned propane powered vehicles are not permitted in underground parkades.) So it becomes preferable to head for higher ground and avoid nearby hollows should certain gases such as chlorine and propane are escaping. Anhydrous ammonia is another fairly common cargo that is real nasty if it leaks.
But dangerous leaks are extremely uncommon except in cases of high energy derailments, and even then most tankcars remain intact. So no valid reason to be paranoid about that rail line past your back yard!
Propane leak = uphill and upwind.
BLEVE is an acronym for Boiling Liquid Expanding Vapor Explosion. They aren’t limited to LP - a 55 gallon drum could go under the right conditions.
PNWRMNM’s explanation as to why they happen is spot on with what I learned in HazMat class. At Oneonta, NY, the cars involved had derailed and were in various positions other than upright. In a situation like that, a relief valve blowing off (and afire) may be directed at another car, which I believe happened there. It was a rural setting, so the fire department couldn’t get enough water to cool the point of impingment.
And that’s how we were trained - put copious amounts of water on the point of impingment (using an unmanned nozzle).
As I recall from the training, one end of one of the cars that did explode travelled some 3000’ before being stopped by a riverbank.
(Edit - had the distance wrong…)
I know it is not a ‘recent event’ but it was one of the more spectacular events that st the time counted as ‘one of the most’ types of BLEVE’s of record. Feburary 24,1978 is a date that many in West Tennessee will remember, it was a derailment of an LPG tanker car that resulted in the deaths of 16 people, directly and indirectly, in thet BLEVE.
Here is a link to one account, which is a pretty accurate representation of that L&NRR derailment in the downtown area of Waverly, Tenn.
Linked @ https://en.wikipedia.org/wiki/Waverly,_Tennessee,_tank_car_explosion
Your description of a propane tank failure is very similar to a steam locomotive boiler explosion, with the “no liquid behind it” equivalent to no water over the crown sheet. In both cases the liquid temperature well above the boili
Sam,
Waverly is a case of applying the term to an event that does not meet the defintion. It is a perfect example of muddled thinking, and a fine example of why I never used the word BLEVE. I was at Bureau Headquarters as the supervisor of our 17 man field inspection force and KNOW what happened.
The short story is this. The car was involved in a derailment. The car was moved out of the track bed and placed upright on the ground. Something like 24-30 hours after the derailment, the tank failed without any fire anywhere in the area before the failure. There was no boiling liquid. It was just sitting there under pressure like it always does.
The rest of the story is that the car passed over something, most likely a rail head, that put a long more or less horizontal dent, or crease, in the side of the tank. The tank fractured along that long dent. When I taught at the Tank Car School at Pueblo I did an hour long discussion explaining the Waverly event in detail, and how to determine how sharp a dent (radius of curviture) is too sharp.
The cure would have been to flare the vapor. Nobody knew what they were looking at. The L&N did not call us, so the Bureau Inspector was not there. Only two of our 17 guys would probably have recognized the risk associated with that damage. The L&N probably saved our man’s life.
The time line in the wiki article is probably correct. The cause the author ascribes to the NTSB is incorrect. Without the NTSB report I can not tell if the NTSB did not get it right or if the author has no idea what he is talking about. Both could be true.
Mac McCulloch
Many people heat hpomes with propane and more have propane gas grills and/or RV’s with propane for cooking, water heating and heaters. It is a very common fuel but it is easy to forget the energy a tank of it contains. RV’s are required in many places to have the tanks sealed closed such as onboard the Alaska Marine Highway ships, and in many tunnels.
I always got a small chuckle out of the Commercials that used the expression “GAS does the big jobs better!” and thinking BOOM. As with many things, there are risks and too many people don’t respect them.
First responders are well aware of them and unfortunately can’t teach enough school kids about them though they try.
Several years ago some fellows decided to couple some Tannerite with an LP tank - I don’t recall if they were taking out a beaver dam or just making noise.
To say a lot of people heard it would be an understatement…