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Tripp Westbrook (Tripp)
| | Posted on Friday, August 23, 2002 - 10:29 am: | 
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I was just wondering (since it's hot as hell here in texas at the moment) if there is any concern about roof rack mounted jerry cans of fuel sitting out in the hot sun for hours on end.
The air temp can easily get over 100, not to mention metal sitting in direct sunlight.
I would think that this would not be good for gasoline in cans.
Am I missing something here? |
Al Oliveira (Offroaddisco)
| | Posted on Friday, August 23, 2002 - 10:40 am: |
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I would think that if the can is full and has little air in it you *should* be okay. Lots of military vehicles carry fuel this way. Both Diesel and Petrol. |
Tripp Westbrook (Tripp)
| | Posted on Friday, August 23, 2002 - 11:27 am: |
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Sure. Diesel isn't a problem that way and I think that most military vehicles are diesel.
I figured that if the can were full (of gasoline) that volatility would be reduced. But I would think that carrying a can that was only half or a quarter full would raise issues.
I suppose that obviously an empty can would have to be left open to vent. |
Paul T. Schram (Paulschram)
| | Posted on Friday, August 23, 2002 - 11:27 am: |
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If the can is full, you have no headspace for the liquid to expand into and the liquid is not compressible, but the gas above it is. Hence, you have a greater likelihood of unfortunate experiences with a completely filled container.
I don't know about military vehicles, but I do know about industrial vessels and we never fill them all the way for just this reason. In fact, in the Large Quantity Hazardous Waste Generator training I administer, I tell my guys not to fill the drums to more than six inches from the top of the drum as the materials we dispose of have a great expansion coefficient. This topic is also exhaustively covered in the Certified Hazardous Materials Manager's test.
The absolute temperature isn't the real issue here, it is the temperature difference the cans will see. If the temperature is going to vary widely, the amount of headspace required increases.
I don't have the coefficient of volume expansion for gasoline due to temperature, but I would suggest at least a 10% ullage in the can to ensure you don't blow the lids off.
On the other hand,if the temperature is going to fall precipitously, you run the risk of your container imploding. I don't know what sort of fittings your jerry cans have, but Justrite makes a great conservation valve (2" NPTM) that will vent in both directions to keep vessels from imploding or exploding by venting anytime the pressure differential exceeds ~1-2 PSI. |
Tripp Westbrook (Tripp)
| | Posted on Friday, August 23, 2002 - 11:32 am: |
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Thanks Paul that's great information.
There can be quite a swing in temp over the course of a day out in the desert but by what you're saying I should be ok as long as the cans are vented properly.
Great to know. |
Al Oliveira (Offroaddisco)
| | Posted on Friday, August 23, 2002 - 11:38 am: |
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Good explanation Paul. I'll have to stop filling my cans up all the way. But what about the fact that gas vapor explodes while fuel will just burn? |
Paul T. Schram (Paulschram)
| | Posted on Friday, August 23, 2002 - 11:39 am: |
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Vent them properly and make sure that you have plenty of ullage in the cans so that when it expands,it won't puke out onto your hot truck roof.
Glad I could help. |
Paul T. Schram (Paulschram)
| | Posted on Friday, August 23, 2002 - 12:13 pm: |
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Well Al, it is the vapors that are burning, in every situation (I know we have some professional firefighters on the board, where's one when I need one!). We heat materials until they generate a vapor (or gas) and it is the gas that burns. In very few situations (which we will never encounter in most cases, unless you're a rocket fuel scientist) will this not be the case.
The idea here is that regardless of whether or not the headspace is filled with volatilized material, it is still safer contained in the can.
Explosions occur when a burning material is not allowed to burn at atmospheric pressure and it is the rapid release of that pressure that results in your explosion. While I'm not a combustion engineer, I have had to sit through a number of hazardous materials training sessions where such things were discussed. When you see gasoline explode at amospheric pressure, you're seeing the flame front rapidly propagating and looking for all the world like an explosion, but for something to actually explode, you must have the increase in pressure due to liquid boiling, vaporising and the instantaneous release of that pressure as the vessel wall integrity is breached. The fire service fellas call this a BLEVE or BLEVI for Boiling Liquid Expanding Vapor Explosion or Incident. BLEVEs are bad things!
To complicate things, there are also conflagrations and deflagrations, depending upon the speed at which the flame front travels. I'd go further, but I get them mixed up!
Most of the time, I don't worry about my employer complaining about my time spent on-line, but this is quickly becoming a safety/emergency response consulting situation that might get me into trouble-oh well, I'd rather be a Rover wrench anyway!
FWIW, Diesel fuel is every bit as dangerous as gasoline if allowed to burn in a situation where it is not vented. I have had fire training folks equate a gallon of diesel fuel to a given number of sticks of dynamite and say that in some cases, it can be more dangerous than gasoline as it won't disperse and the fire danger remains far longer. Also, lay people are more careless around diesel fuel as it is typically much safer to handle.
We can continue this conversation to include such things as flash point and auto-ignition if anybody is interested! Man, am I a nerd or what?
Peace,
Paul |
Rob Davison (Pokerob)
| | Posted on Friday, August 23, 2002 - 12:22 pm: |
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so what you are saying is if i go swimming in a tank of gasoline and someone throw a match in, i'll be okay unless i come for air 
rd |
Al Oliveira (Offroaddisco)
| | Posted on Friday, August 23, 2002 - 12:46 pm: |
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I think that's what he's saying and it makes sense. Air is the oxidizer. But I'm not going to set out to prove him right or wrong.
I would still rather have a tank that has more fuel than air but I'll now keep a gap on top of the can when I fill up. |
Paul T. Schram (Paulschram)
| | Posted on Friday, August 23, 2002 - 05:03 pm: |
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Well, it isn't exactly what I'm saying, but if I've convinced you to leave some headspace in your containers and to consider vents, my work here is done, or as I say at work, "I have extinguished my responsiblity-any unsafe acts from here on out are your responsibility".
I'm going home and hope to not have to do any more safety stuff (other than trying not to hurt myself) until Monday.
Be safe
Paul |
Bill Molnar (Circekat)
| | Posted on Monday, August 26, 2002 - 11:03 pm: |
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Fire Science 101:
Materials themselves never burn, they heat enought to cause pyrolysis (releasing of flammable vapors) which is what actually ignites and burns. Watch a log in the fireplace or a candle sometime.
Flammable material safety: never fill a flammable liquid container over 90% of total capacity of entire container to allow for expansion and contraction of liquid due to temperature. This is why you can fit about 1.5 gallons into a 1.25 gallon gas can for the lawn mower. Always leave these containers fully sealed during transport. Most Jerry cans are vented within the first quarter turn of the top, thereby releasing vapor pressure from the fully sealed transport state. This is usually done by a small pinhole vent created by the manufacturer of the container.
Hollywood Special Effect Trick of the Trade: The famous exploding car is the vehicles gas tank (that has been scored for safety) with about one pint of gasoline in it. The ignition source is a spark plug. This gives a safety feature (scored tanks do not hold extreme pressure), a very good fuel to air vaporization mixture and a controlled explosion from a person sparking the plug. Keep the tank from having a large surface for vaporization to occur from and the chance of an explosion decreases at the same rate.
Paul: conflag is rapid advance of thermal wave causing residuals, i.e. explosion or BLEVE; deflag is slower advance based upon feeding to move. Pine trees are a most excellent bleve source. |
Rob Davison (Pokerob)
| | Posted on Monday, August 26, 2002 - 11:24 pm: |
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Quote:Most Jerry cans are vented within the first quarter turn of the top, thereby releasing vapor pressure from the fully sealed transport state. This is usually done by a small pinhole vent created by the manufacturer of the container.
okay now what if you have the good kind of can that doesn't unscreew
rd |
Bill Molnar (Circekat)
| | Posted on Tuesday, August 27, 2002 - 07:03 pm: |
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How do you get your items into the Jerry can? The cap (top) is what I was talking about.
Bill M. |
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