Propane safety

sounds like a cool teacher - closest we got to that was the teacher (behind a thick layer of perspex screening) chucking a lump of potassium into a bowl of water - fizzy blue flame and it whizzes all over the place. We never got to try it of course.

 

hi Tops, what device did you put on the tank? What then happened to the gas? Did you take the bottle back to the dealer? Did your car fill with gas on the way?? Having trouble picturing this situation? Thank you

 

Ok so what about if you get your air source back firing/malfunctioning whilst the propane is burning (or before it is lit) how to prevent/control this hazard?

Been reading a bit more, you need the air to combust the propane (quicker? hotter?) and to force the fuel to swirl around the crucible to heat it evenly?

 

Remembered an experiment done with another artist way back - built a furnace in an hour - metal tin from B&Q, ceramic wool, small propane tank and burner, crucible and bronze bits. Melted in twenty minutes. The crucible was on a brick inside the furnace, the propane was coming in one side and we didn't move it, and there was no air source. Was this phenomenally lucky/stupid? What were the dangers here? I think the crucible could have been weakened on one side by the heat being in one place, especially if this wasn't changed during subsequent melts, not sure what else?

 

Just put the 'device' back on the bottle and close that valve (green arrow) if the internal shutoff on the cylinder/bottle fails (red arrow) and store safely and consume first.
It's not worth the petrol or risk to take it back. Better yet, hook it to a compatible camp stove and make dinner until the bottle is empty and dispose properly. One time this happened, the first torch was also leaky at its valve so I had to move the defective bottle to a second torch, all out in the shed (not in a dwelling).

 

Hi tops, thanks for the further info -

so for a canister this size, https://www.flogas.co.uk/product/6kg-propane-gas-cylinder I should have a couple of compatible extra torches hanging around in case I need to bung one on and close the valve? sounds like a good idea, thanks I wouldn't have thought of that.

I imagine that was many dinners you made if it was a full bottle!

 

My operation is super small, I use the the 20 pound 'BBQ' bottles (maybe the 11kg like your proposal is closer) on my melting furnace. It is a '6kg' furnace so 2kg alu. Mostly doing aluminum (between .25 and .75 kg pours, 8-20-something oz) hoping to do bronze someday. I use the 1 pound bottles for plumbing torches and camp stoves. Torch was used to light paper that lit furnace...

 

Hey Tops, that looks a similar size to what my operation will be like, to start with at least - thanks for the pic. Looks like you have everything you need to do bronze there. How is the Gongyi furnace? Seen these on amazon but holding back on what to get so far, or to make my own.

It really doesn't look so scary from that pic

 

The furnace has been good, it was a get-started type kit with tongs and crucible and I realized that I was only going to save 20$ and spend days making it DIY. Upgrades include a smaller crucible, firebrick plinth to raise crucible, coating the inner bore with refractory cement, a small 3D printed 'horn' around the air intake to prevent cross wind from affecting the flame, and some marks to make setting the airflow somewhat repeatable. Better tongs are in the works and having extra firebricks around to set hot things on makes life easier.

 

Propane is safe stuff. You need a ratio of air to propane right about 16:1 Get it too much lower than that and it just doesn't light. Too much higher it doesn't light. (in playing around with starch projectile accelerators. I think when the mixture got over 18-20:1 or under about 13-14:1 it wouldn't cycle properly (potato didn't fly))The odorant that they add (methyl mercaptan) is something humans smell in very low quantities (it's given off by rotting food. So we've gotten good at noticing it). You should smell it way before it's at a level that it's going to ignite. If I'm going to transport it inside the car I make sure to crack open a window or two. The odor can annoy folks and the tanks can smell for a while after you fill them. That smell just kinda hangs in the car like the morning after $1 beers and burritos night at the local pub. As noted by others you need to check your setup every now and then for leaks and it if you notice as smell look into it. If you have a tank that's leaking and you can't do anything about it (night, weekend, shops closed) get it out of the house/building/car etc. Sit it out in the yard (on the roof of your building) anywhere there's plenty of fresh air. Because propane needs a very controlled ratio of fuel and air to burn it's not likely to ignite sitting out side slow leaking over night. Plus you don't have to smell it. IF you are using rubber fuel lines and your rig is stored outside/in a shed/in a garage (any place that rodents or other chewy critters show up you should visually check your lines before each casting session. Soap check every so often (you're the one playing with fire you decide what level of risk is acceptable to you!!)

Bruce

 

Not sure exactly what you mean but the air source won't push air into the propane bottle with a fan/blower. It just doesn't have the power to do that.

The blower adds enough air to burn the large amount of propane that you have to put out. It causes the temperature in the furnace to get a lot hotter with an air source. It just replaces the oxygen thats used up in the furnace.

What crazybillybob said is right. The ratio is pretty precise to get propane to burn. It's pretty specific. I used to be super concerned as well but after building several burners and furnaces I figured out that it is fairly safe unless you let the flames directly hit the propane bottle you're good to go for the most part.

 

The pressure in a propane cylinder can be upto 200 psi. Standard atmospheric pressure is about 14 psi.
So as Zapins says air is not going to backflow into the cylinder unless the cylinder pressure is less than atmospheric pressure

 

Thank you, does this risk get any greater as the cylinder gets more empty? the atmospheric pressure goes down right? I remember that from scuba training...

Maybe wouldn't be low enough to cause a back flow issue at any point though?

 

So long as there's liquid propane in the cylinder to phase change into gas, the cylinder pressure will stay constant. Even in a completely empty cylinder the cylinder and atmospheric pressures would be be equal and no air would get into the cylinder. There would be some situations involving leaving the empty cylinder valve open for days, with daily heating and nighttime cooling but a readily available check valve would prevent even that.

 

I can think of only one situation where air will back flow into the tank. If there was very little gas left in the tank, almost the same as atmospheric pressure then the temperature dropped really low causing the remaining gas condensed to a liquid resulting in the pressure in the tank dropping below atmospheric. then open the valve and air will flow it to balance the pressure. but then there may not be enough gas and air in the tank to cause it to explode.

 

How low a temp are we talking here?

 

A quick google says -42 deg C

 

Modern propane tanks have check valves in them to keep this from happening. As long as the tank you're using is up to date with it's certification. Without tampering with the valve unit you're very safe using propane tanks for foundry / forge usage as long as the burner is not pointed at the tank and the hoses are in good repair.
Your burner is going to stop operating effectively long before the tank is empty to the point that you have to worry about to theoretical aspiration of atmosphere into the tank.

 

Hi Zapins,

I wasn't sure what I meant by that either as I was mentally referencing a post from here I didn't save ..found it now

If a blower failure of any kind, there would still be 10-12 PSI of propane being introduced to the furnace, the flame would fail but what about the 10-12 PSI being introduced to the furnace (most likely cherry hot)? I could see a possible hazardous situation w/ gas accumulating in the furnace and finding any air supply to reignite, even back through the forced air supply.
From
https://forums.thehomefoundry.org/i...ne-burner-question-re-safety.1603/#post-36253

So in this situation the danger is the lack of air? I don't quite understand. Surely if you take away one source of the 'fire triangle' (fuel, oxygen, spark?) then you won't get it burning?

Still thinking about the backyard furnace made previously, (post above: built a furnace in an hour - metal tin from B&Q, ceramic wool, small propane tank and burner, crucible and bronze bits. Melted in twenty minutes. The crucible was on a brick inside the furnace, the propane was coming in one side and we didn't move it, and there was no air source. Was this phenomenally lucky/stupid?)
perhaps the burner was drawing in air, I suppose it wouldn't have lit otherwise?