Building Explosion Analysis (PLEASE HELP!)
 

I would like to apologize in advance if this is not the correct forum for my post. A few months ago there was a fire explosion on my property that completed destroyed a water treatment plant housed inside a 24' X 32' X 20' building. The force of the explosion was so great that it blew down a 24 feet wide vertical metal sectional garage door off of its tracks, and the heat was so intense that it destroyed everything inside the building. Regrettably, this water treatment facility inside the building was not covered by insurance!


GOOGLE DRIVE PHOTOS

This fire was investigated by both the local fire marshal and a cause-of-origin fire investigator (hired by the insurance company), they both determined the explosion was due by a leaking 130 Gallon Propane tank located right outside the building and ignited by the heater. In fact, the fire marshal took pictures showing visible gas vapors escaping from the heavily corroded bottom of the gas tank. The gas company (a large multi-billion company in US) actually admitted that they filled (pressurized) the tank on the morning of the explosion (which accelerated the leak), and their maintenance record has confirmed the tank has never been replaced or maintained for at least 20 years! With so much evidence pointing to the leaking gas tank as the cause, we expect this big billion dollar gas company to pay for the fire damages? Unfortunately, NO.

The big gas company commissioned Gene Mcdowell - a certified Fire and Explosion Investigator (License 4208-0736) based in Houston, who authored a report claiming that this accident was not a propane fueled chemical combustion event that blew down the metal garage door and destroyed the building, instead the damages were caused by ESCAPED HIGH VELOCITY AIR from a 119 Gallon Well Pressure Tank (Model Well-Rite WR-360, 16 gauge cold rolled steel wall, contains inert air pressurized at 38 PSI). For some background, the purpose of this low pressure 119 Gallon air tank was to prevent backflow of well water into the water pipes. Mr. Mcdowell claims the WR-360 tank was ruptured by heat caused by a secondary fire triggered by an unidentified ignition source burning an unidentified fuel stock (lots of unknowns). Citing this report, the gas company has refused to reimbursed for the damages. Hopefully with the help of smart kind souls in this forum, I can somehow quantitatively disproof Mr. Mcdowell's outlandish theory.

Intuitively I know that only an exothermic chemical reaction can create enough air pressure to blow down a metal garage door, because a 119 Gallon air tank pressurized at 38 PSI simply does not have enough air molecules to cause that magnitude of damage. I do not have any simulation software and am not trained in this field, could anyone help me to quantitatively prove (even just at the order of magniturde level) required to do this type of damage? I really appreciate your help!

Not an expert or a lawyer. Here are my observations. Maybe someone else can do the more complicated calculations required.



38 PSI = 2.6 bars = 2.58 Atmospheres of pressure (source : duckduckgo converter)
A coca cola bottle can hold max 100 PSI.
Comparing the two, 38 PSI seems pretty low.



You'll need to find the pressure rating of your ruptured vessel. That would give you the internal pressure at the point of rupture.


You'll need to find the mass of fluid that was present in the vessel before the accident. You'll need to find the temperature of the fire and how long it lasted to evaporate the fluid and pressurize the tank.


Based on those, maybe someone can calculate the velocity at rupture.


Since you showed many items nearby, try to see if many items or equipments in its path were destroyed or not.


Edit : Rethinking about your problem, there's good news and bad news.


Bad news - rocket pressure vessels are sometimes rated to rupture at 5 to 6 times their nominal working pressure. So, your pressure vessel would probably need to be at a very high pressure to rupture too. And that rupture might just be strong enough to cause the damage. But you'll need the help of the experts to verify if that happened.


Good news - What caused the rupture? If the fire was started due to negligence of the company, then you might have a good case.


Asking your question in other forums might also be helpful. Reddit has a lot of forums that deal with industrial failures such as this. https://www.reddit.com/r/catastrophicfailure has some people who know well about OSHA and how accidents can happen. I don't know if they take questions though.

Approximate Force Required?
 

Hi Sayan,

Thanks for your reply. This information I seek will not be used in any legal proceedings, nor will it be interpreted as legal advice of any sort, just looking for some unbiased science calculations.

I'm simply looking for a few back-of-the-envelop calculations on the force it would take to blow down a 24 feet metal garage door, and the amount of force that can be generated from a 119 Gallon metal container.

This is my thinking process...The garage door was blown down from an "event", the event applied enough force on the door to push it off its tracks, and that force can only be imparted by fast moving air. And in my untrained mind, there need to be quite a bit of air molecules moving very fast to impart the force necessary to push the metal door down (think hurricane force wind). Can the magnitude of this force be quantified?

The gas company claimed that air from the 119 Gallon container somehow pushed the door down. The amount of air molecules in the WR-360 is limited and can probably be calculated, and there are probably some equation that calculates the force this amount of molecules can generate....I expect the math will show that the force from the container is not on the same scale as the force required to blow down a metal door.

This is where I could use the help of someone smarter than me from this forum...

Just my two cents as a senior (biomedical and) mechanical engineering student... Similarly, I cannot give legal advice or anything.

With an explosion within a confined space, two types of typical pressure loads will be generated: shock wave and quasi-static pressure.

The first shock wave is decisive; the quasi-static pressure is considered a decisive factor that triggers structural disintegration and overall destruction based on structural and local damage. Therefore, the first incident shock wave and quasi-static pressure are important factors for analyzing and evaluating the damage effect.

I do not know if you can solve the equations for each though, as there may be some unknowns you wouldn't know/need to find out.
First, to calculate the reflected shock wave pressure, the incident shock wave pressure should be calculated first.
Then, the peak overpressure of the quasi-static pressure is determined by the total energy released by the explosion and the volume of the garage.

My information comes from this paper, and contains the equations for the reflected shock wave pressure and quasi-static pressure:
https://www.hindawi.com/journals/sv/2019/6862134/

Hopefully that could be a good jumping-off point. Calculating the the total energy released by the explosion might be difficult, but we know properties and volume of propane. Then, (sorry if this is going down a rabbit hole) we would probably use thick/thin-walled cylinder approximation (16 gauge = 1/16 inch = 1.58 mm, so probably thin walled approximation based on the radius). To be able to determine the force of the explosion from the tank itself, as aerosayan mentioned, the force is 5-6X as the pressurized tank. The thickness and material (Young's Modulus) of the door would probably also be required for such a calculation (the resistance the door would have).

So, this is for sure a multi-part problem. Some of this may be irrelevant, but it's a discussion forum, so I feel like suggestions can't hurt.

You're correct. However we can simplify the problem at hand and see if the pressures generated by the explosion would be enough to cause such structural damage.

I'm considering that we can find out the fluid pressure inside the vessel when it exploded from the manufacturer's safety compliance reports.

OP currently has the hypothesis that since there wasn't much air molecules inside the vessel, it wouldn't cause much damage. I think that's only true when the explosion wave is subsonic. But in this case, I think that the explosion wave will most likely be supersonic, and will generate an expanding blast wave front.

That blast wave will cause overpressure as it compresses the air in the room, and it will generate high velocity winds that go towards the explosion origin.

I referred the wiki page, and a cdc pdf for the effect of blastwave overpressure on humans and structures.

https://en.wikipedia.org/wiki/Overpressure
https://www.cdc.gov/niosh/docket/arc...geChambers.pdf

There are many PSI values given in the references, but both agree that most buildings collapse (except concrete buildings as per the wiki) at 5 PSI overpressure.

Maybe someone in this forum can do a Sedov-Blast simulation in 2D or 3D to see what kinds of overpressure will be generated in the room?

Regards
~sayan

Wr-360 specs
 

Yes, the challenge is to quantify the "order of magnitudes" of force created and that WR-360 can not be the culprit (based on reasonable assumptions). As you can see from the pictures (in Google folder), there are all sorts of light weight debris laying undisturbed on the floor near the ruptured WR-360, so there is visual evidence that the air escaped from the WR-360 did not create a "gale force wind" that may take down the garage door. But the gas company pointed to Mr. McDowell's report (based on some pseudo science) and hid behind his years of experience. They have asked me to show some evidences of why Mr. McDowell's analysis is faulty.

GOOGLE PHOTO FOLDER

The spec of the WR-360 says that the maximum pressure the tank can take is 125 PSI. And the physical dimensions is in the second doc:

WR-360 MAX PRESSURE
WR-360 PHYSICAL SPEC

On the speed of the explosion wave, Mr. McDowell claims that the tank was ruptured due to overpressure from the heat cause by a fire (not involving the propane). So if the max pressure the tank can take is 125 PSI, and the max working temperature is 140F, is it possible for this to create a supersonic wave? And how much destructive power could this rupture cause?

On "building collapse at 6 PSI"....Does that assume an air-tight building with no other egress? Because wouldn't air first escape from the weakest points, like a window or a door? In the photos, you can see that some of the green windows were also blown out.

I don't have the mathematical answer to that, since I don't have any powerful PC or easy to use software like ANSYS to run the simulations I mentioned before.


125 PSI is roughly equal to 8.5 Atmospheres of pressure. Since there is such a high difference in pressure between the internals of the tank, and the atmosphere, as soon as the tank membrane ruptures, it will explode out.


My intuition tells me that such a high pressure difference would cause an explosion with a supersonic blastwave front.


I searched on Youtube "pressure vessel explosion" and found this good explanation and a pressure vessel explosion demonstration : https://youtu.be/iH5bT7xk_Rw


There is a high chance that the investigator might be right about the ruptured vessel causing the damage. And since the rupture seam is directed towards the front, it makes sense why most of the blast will be directed towards the front. In fact, since the energy has only one way to exit (through the rupture seam), the blastwave may actually be stronger in this case.


However, the explosion didn't happen out of nowhere. The rise of pressure from 38 to 125 PSI happened due to heat. Since you told that the investigators found out that the cause of fire was from the leaking gas tank (If I understand correctly, the company is responsible for maintaining the safety of the gas tank?) ,



So, In my opinion(not a lawyer) they maybe liable for the damage.



I think due to the rupture seam, the blastwave was directional (like a shaped charge), and most of the energy will be directed towards the front. The thing I don't understand, is how the thin wall at the front still standing, while the heavy doors got thrashed around.

Also see in the video I linked above ( https://youtu.be/iH5bT7xk_Rw ) at around 1:25 a supersonic blastwave is generated that forms a cloud like spherical layer around the explosion region, and then goes out of camera range even faster than the flames exploding out.

Ohhhhh..... that's a trap if I've seen one.


The company can tell you to do anything it wants.. it can tell you that a monkey has determined that quantum mechanics was the reason why your property got damaged. And then they'll ask you to prove quantum mechanics wrong.


Don't fall for their trap. If the math (by an expert in pressure vessel explosion and not some internet random person) says that the investigator is right, don't try to prove him wrong.


Try to make your case (after consulting a lawyer) that your pressure vessel only failed due to the fire (38PSI->125PSI pressure rise) which happened due to their negligence in repairing and/or replacement and/or over-pressurization of the leaking gas tank.





Your workshop would definitely have the pressure vessel, like many workshops.

Even if there was a motorbike with gasoline in the tank, the fire would've exploded it and caused similar damage, some workers could actually get injured or killed. The prime reason for the explosion was the fire and the gas leak, any and all damage due to that fire is fully the responsibility of the party responsible for the fire.

I am very sorry, please allow me to clarify...There are TWO tanks in question. The first is a 120 Gallon propane tank (full with propane), it has a visible leak, and is located right OUTSIDE of the building. The fire marshal believed the leaked propane from this tank seeped into the building and the Resner heater inside the building at night triggered the explosion.

PICTURE OF PROPANE TANK LOCATION
PICTURE OF LEAKING GAS

Inside the building, there is another tank. It is a 119 Gallon tank (WR-360) that is filled with AIR and pressurized at 38 PSI. As you can see, this tank was ruptured. The gas company claims the air escaping from this 119 Gallon tank has blown down the garage door, and none of the damage you see was caused by a propane explosion (a bit ridiculous). Because if propane was involved, then it would clearly be their fault, as they have already admitted to the leak. So if I can show an analysis that the WR-360 scenario is impossible, then a propane explosion would be the only possible cause.

PICTURE OF WR-360 FILLED WITH AIR
DAMAGE CAUSED BY THE EVENT

I'm still waiting for other members' perspective and opinion on the matter, but since you told that there was only air inside the pressure vessel, there is a possibility of a different mode of failure.


If there was water inside, the vessel would most likely fail at 125PSI.
Since there is only air, the material could have also failed at a lower pressure, since there is no water inside to cool the vessel and protecting the material from the heat.


I don't know if this was the case, but that is a possibility.

My understanding is that there is usually between 5 gallons to 40 gallons of water inside, depending on the pressurization inside the pipes. If the pipe pressure is low, then less water in the tank. Though the WR-360 is definitely not filled full with water, but there is some water inside.

If there's water inside, the heat will vaporize it and cause pressure rise in the tank. Even 5 gallons would probably be enough to create enough vapor pressure to reach 125PSI. This is the most likely mode of failure.

Clarke,


The gas company is telling you that the door didn't break because of the fire, is to save them some money. They know they have to pay up, so they have their employees calculate the minimum amount of money they have to pay to you. You would've surely filed a claim for "fire damage".

The language is specific in the eyes of the law. Pay attention.



When they say that the damaged door wasn't due to "fire damage", but due to "explosion of the pressure vessel", they are technically telling half of the truth and they have an expert backup their "statement". Now your "fire damage" claim doesn't hold up for the door, as they've "stated" that it was not due to "fire damage", But since their rejection is still a "statement", and still up for debate in the eyes of law (as you could make a case that your pressure vessel was safe for use until the fire started due to the company's negligence), you can refute their "statement" by saying that it was exactly due to "fire damage" due to their negligence.


Let's say that someone was unfortunately injured by the "explosion", then wouldn't the gas company be liable under their "fiire damage" terms and conditions?



Read their Terms and Conditions that you've signed, to see what definition they've given for "fire damage" and what they'll cover in case of an accident.



Of course consult a lawyer first if you're not sure.

I think what we need is to calculate the MAX AMOUNT of destructive energy that can come out of this tank, when it is heated hot enough to rupture.

This thread may have too much details and takes too long to read, any thoughts on how we can distill this down into a small "math problem"?