From: John De Armond
Subject: Re: Refill propane
Date: Sat, 03 Jun 2000 17:48:53 EDT
Newsgroups: rec.outdoors.rv-travel

"George E. Cawthon" wrote:

> A guy in Lewiston Idaho was supposedly blown up by his barbecue.  I
> couldn't understand how a barbecue could blow up and kill someone so I
> asked my brother-in-law who is an engineer.  He said the guy had had his
> tank filled but they filled it too full.  He open the valve on his tank
> and the valve on the barbecue and liquid propane flowed in.  When he hit
> the start button it literally exploded, killing him.

No, sorry.  If liquid propane had reached the grill, it would have
flooded the thing and been too rich to burn.

I know how to blow up a gas grill because wifey did it.  Just turn
the gas on with the lid down, go off and do something else and 15
minutes later, remember that you forgot to push the red button. 
Push the red button.  Then retrieve the grill lid from the roof of
the house.  The force necessary to toss a grill lid 100 feet or more
would certainly have been enough to kill, had someone been leaning
over the lid when it went off.

From: John De Armond
Subject: Re: Refill propane
Date: Sun, 04 Jun 2000 01:23:00 EDT
Newsgroups: rec.outdoors.rv-travel

"George E. Cawthon" wrote:
> 
> Neon John wrote:
> >
> > "George E. Cawthon" wrote:
> >
> > > A guy in Lewiston Idaho was supposedly blown up by his barbecue.  I
> > > couldn't understand how a barbecue could blow up and kill someone so I
> > > asked my brother-in-law who is an engineer.  He said the guy had had his
> > > tank filled but they filled it too full.  He open the valve on his tank
> > > and the valve on the barbecue and liquid propane flowed in.  When he hit
> > > the start button it literally exploded, killing him.
> >
> > No, sorry.  If liquid propane had reached the grill, it would have
> > flooded the thing and been too rich to burn.


> Too rich is what I though too.  Yet, you say 15 minutes of flow and
> "wifey's" mistake still resulted in an explosive mixture.  About 2
> seconds of liquid would be about the same (just a guess).  The timing
> would have to be exact to get a correct mixture.  Another possibility,
> is that the propane flowed through the holes in the bottom of the
> housing and created an explosive mix in the general vicinity, and he lit
> a cigarette.  Still, the end result no matter what happened was that
> something blew up and he died and it was blamed on a too full tank.
> 
> Sounds like someone needs to experiment to see what would really
> happen.  Not me!

Been there, done that, have the photos... (well, not really photos
but you get the picture... groan)

OK, here's the long answer.  Assume the tank is filled completely
full with no vapor space at all.  When the valve is opened, the
liquid propane in the valve body will flash to gas and flow out,
entraining some liquid in the process.  The regulator will receive
gas with a little liquid.  This does it no harm and it will work
normally.  

Now let's assume that somehow this absolutely full tank begins being
warmed as the valve is opened.  Liquid propane will reach the
regulator.  At first, the regulator will function normally. 
However, since the propane is now being vaporized at the regulator
orifice instead of in the tank. the regulator is refrigerated.
Eventually it will begin to frost.  Further down the line, the
diaphragm will become so cold that it stiffens.  The regulator will
then lose control.  The downstream pressure will rise until the aux
relief diaphragm (usually plastic and not affected by the cold)
lifts to vent the excess pressure to atmosphere.  Because liquid is
in the regulator, some volume of gas and liquid will discharge from
the atmospheric vent until sufficient liquid is removed from the
tank to no longer feed from the valve.  Since liquid propane
compresses very little and the steel tank expands very little, the
amount of liquid involved is small.

I know that this is the sequence of events because I've tried
operating a tank upside down trying to force more BTUs through a
small regulator than it was designed for.  The (correct) logic was
that if the metering orifice is metering liquid propane instead of
gaseous propane, more volume would be available.  It worked for
awhile until the regulator froze, whereupon liquid propane spewed
from the atmospheric vent.  Had I supplied heat to the regulator, it
would have continued to work and would be functioning in a manner
almost identical to the fuel vaporizer used on propane-powered
vehicles.


Obviously if there were flame present, the escaping gas would
ignite.  The chance of an explosion in this situation is slim.  Big
fire maybe but not an explosion.

Now consider the scenario such as my wife went through.  The burner
in the grill is designed to produce an optimal mix of gas/air.  This
is also the optimally explosive mix.  It is overwhelmingly likely
that this guy who was killed simply ignited an explosive mix in the
grill just like my wife did.  Had my wife not squatted down so that
she could see the little red button before pushing it, she might
very well have been killed.  As it was, she came running to me with
the wildest look I've ever seen :-)

John

From: John De Armond
Subject: Re: Sideways mounted propane tanks
Date: Tue, 14 Mar 2000 21:26:12 EST
Newsgroups: rec.outdoors.rv-travel

Dan Prescher wrote:
> 
> Well, even if they are standard verticals, you can't argue with years of
> faultless horizontal service. Of course, now that the question has been
> raised, there will always be that nagging doubt...
> Kevin Clark <kevinnospamclark@usa.alcatel.com> wrote in message

Actually you can argue and he's just flat lucky.  Here's the issue.

Everyone knows that propane is stored as a liquid in the tank (I
hope everyone knows!)  Just as it takes heat to boil water, it takes
heat to vaporize the propane.  because propane is a good refrigerant
(ASHRAE designation R-500, as it turns out), it takes a lot of
heat.  During normal operation of a tank oriented in the right
direction, over the short term, this heat comes from the liquid
propane itself.  The liquid gets cold. If propane is used fast
enough, the propane will drop below freezing and frost will form on
the tank.  At normal usage rates, the heat used to vaporize the
propane is replaced by heat absorbed from the air surrounding the
tank.  The sensible effect is that the tank becomes slightly cool.

Now consider what happens if the tank is turned sideways so that
liquid propane reaches the regulator.  Now the vaporization and heat
absorption occurs at the metering valve of the regulator.  Since
there is little heat capacity in the mass of the small regulator,
the regulator will rapidly freeze.  How cold it gets depends on how
fast propane is being used.  At a low rate of use, the regulator
might just get cold and sweat.  As use increases, the regulator
starts to freeze.  As heat is withdrawn from the regulator, more and
more liquid propane reaches the low  pressure line before
vaporizing.  In addition, the diaphragm in the regulator gets very
cold and stiff.  At some point, the regulator can no longer meter
the liquid flow well enough and, combined with the liquid
evaporating in the low pressure line, the pressure rises much higher
than normal.  This will cause pilots to blow out, burners to flare
and generally a lot of nasty stuff.  But it gets worse.  there is a
separate relief diaphragm inside the regulator that functions as a
safety atmospheric vent.  When the pressure in the system gets too
high, it lifts and vents propane out the "vent" port on the
regulator body.  So now we have propane venting to air.  It gets
worse.  Since the reason for the overpressure is the frozen
regulator's inability to meter liquid propane, liquid propane will
be discharged from the "vent" port.  At this point, we have burners
flaring and liquid propane escaping from the regulator.  As the
regulator gets colder from this liquid flow, the needle valve loses
more control over the flow from the tank.  Left unchecked,
eventually a geyser of propane liquid will erupt from the vent.  One
can imagine what comes next.

This is not speculation.  Been there, done that, while trying to
fire a homemade blast furnace through a regulator that wasn't nearly
large enough to feed the burner by turning the grill tank upside
down.  Yep, the tank caught on fire and Yep, we watched the thing
burn - from a city block away!

The sole reason this guy's friend has gotten away with it is because
he has not withdrawn propane fast enough yet to cause the regulator
to freeze.  Once the freezing starts, it is a self-perpetuating,
positive feedback situation.  You get a little warning from the
liquid propane fizzing as it hits the ground - but not much.  the
geyser follows shortly.

I'd certainly not want to be in the same campground with this guy!

John

> news:38CEA649.465EDC21@usa.alcatel.com...
> > Dan Prescher wrote:
> >
> > > Are you sure they're standard vertical
> > > tanks?
> >
> > They look exactly like the one on my BBQ.  No feet, and no obvious
> > markings of "Up" or "Down".  I'll look more closely tonight.
> > 
> > I'm pretty sure one of the tanks is original because it has a
> > manufacture date of 10/74 and this is a '75 motorhome.  That tank was
> > recertified in 1986, but I plan to buy a new one now that it is empty.
> > The 2nd tank is not original as it was manufactured somewhere around
> > 1990.
> >
> > KRC
> >