A giant hairdryer, or something more?

I’m getting mine out of the storage closet now.

I used to just aim it at the cat.

This is a solvable problem. Low temperature flames, such as burning propane, will not pass through a finely meshed metal screen (Crappy link to Flame Arrester Screens ). The screens conduct heat away from the flame too quickly to allow an ignition front to pass through.
A piece of copper windowscreen will prevent zooka explosions. However, the rectangular mesh might mess with vortex formation. If so, a little finite element analysis and custom screen weaving should allow a workable arrester screen design.

I just got back from Vancouver, where the Science museum by the harbour has one of these as large as a trash can.

You can fire it at this matrix of little metal spinners and see the circular ripple pattern where you hit. Even that one isn’t very loud, and I had someone hit my hair with it.

I think this would be an ideal home project, actually.

It is a smoke ring generator!
Take a large rigid can, preferably metal, but plasic will do.
Cut a neat round hole, 1 to 2" dia. in the bottom.
Stretch a "drum head over the open end and secure to rim.
Light a ‘SMALL’ piece of cotton waste, extinguish flame, but allow it to smoulder and make smoke, and insert in the round hole.
Strike the center of the drum with a round ball on a stick or some such.
Watch the smoke ring travel through space.
CAUTION – ADULTS ONLY. Fill the can with flamable vapors. Direct the “varor/smoke rings” toward an open flame some distance away…

A cigaret company had a large smoke ring generator sign over Times Square" in NY some years ago.

I have conducted the ring of fire experiment!

The vortex cannon was constructed from a sturdy plastic container (held sodium hydroxide pellets). It was cylindrical, about four inches diameter and four inches high, with a large screw top. I made a hole about an inch in diameter in the bottom using the conical grinding stone attachment of a dremel tool. The hole was only approximately circular, and the edges were’t well finished.

A sheet of plastic from a shopping bag was placed over the large threaded opening of the container and secured with string. The string was tightened by passing a straightened paperclip beneath it and repeatedly twisting. This made a surprisingly good seal, which was important for the gas filling.

Although no Airzooka, a pellet of smouldering paper in the device produced smoke rings about 2 inches in diameter, and it could snuff a candle at 2 feet.

The gas source was an aerosol “air duster”. The gas was not listed, but from the smell, di-methyl-ether was at least a constituent. I suspect it was either pure DME or a DME-butane blend. The can was labelled “CFC free” and “highly flammable”.

A length of 5mm heat-shrink tube was placed over the stem of the air duster and shrunk onto it with a paint stripper. This allowed the vortex cannon to be filled with gas by inverting it in a bucket of water and bubbling it full using the heat-shrink tube. It was then fired at the candle, in a garage away from anything flammable. Safety precautions included overalls, gloves and safetly specs, although the quantity of gas involved was small.

I am sad to report that the vortex rings of “highly flammable” gas snuffed the candle just as effectively as air. Despite repeated attempts at various ranges, using fast rings and slow rings, I couldn’t get the things to light. I could even make the candle flame flicker without going out, but still no ring of flame.

A repeat of the experiment using a camping stove rather than a candle was equally disappointing. I intend to try a few variations (such as using the butane/propane blend from the stove gas cannister) in the near future. I shall report the results here, assuming I don’t get distracted by something equally foolish.

If anyone wishes to emulate me, please be aware of the risks involved. You do feel a bit of idiot wearing a load of safety gear to blow candles out, but there is a real potential to get hurt here.

Wasn’t the Wham-O Air Blaster taken off the market for safety? I seem to remember they were worried about hearing damage from close-range use.

But then again, it’s easy to freak out a cat!!

What is it with you people and tormenting cats?

Don’t you realize that you have to sleep sometime?

Darn. What was the shortest distance to the candle that you felt was reasonably safe?

(DISCLAIMER: The following suggestions could be very dangerous. Use at your own risk.)

What next? A mist/fog of flammable liquid? Flammable dust or powder?

I varied the distance between 3ft and 1ft. I actually thought that the 3ft shots had a better chance - more gas-air mixing, but on the other hand it was harder to be sure they were aimed at the candle.
I was planning to buy an actual Airzooka and have a go with that. The bigger rings might have improved the situation. Unfortunately the local Gadget Shop seems to have gone out of business, which has put a crimp in my plans.

Another alternative is different gases - lighter refills should be pure butane, whereas blowtorches are propane. I have access to acetylene but I’m not happy about trying that - too much energy.

Hadn’t thought of fine powder - wasn’t lycopodium powder used to create flame clouds on stage? I might give it a go, but I’ve a few other things to be getting on with at the moment.

Lycopodium spores can be hard to find. Fortunately, common bleached flour will also produce a satisfying fireball (bottom of page).

The entire company went bust, not just your local shop.

But it looks like it’s been bought over and will be back.

BOOOOOO!

HURRAY!

Thanks for the link, Squink. I can now confirm that if a small quantity of Bird’s Custard powder is placed inside the vortex cannon and shaken to put it in suspension, it can be puffed out the hole. It doesn’t seem to make well-formed rings, and doesn’t ignite when puffed at a candle flame. I might try flour or icing sugar at a later date, but powders are messy!

It has occurred to me that if the thing is filled from the end of a propane blowtorch or a bunsen burner with the hole open, it will be filling with a well-mixed gas-air mixture rather than a pure gas. Unfortunately I have neither readily available - I’ll see what we have at work.

As stated in most of the references to combustible powders/dust they will burn rapidly if not explode. The principal requirement is that they be very fine/small particles.

Smoke ring devices seem to propel a toroidal ring of smoke or whatever is in the drum. If aimed directly at a candle they blow out the flame. If travelling slow enough and are just grazing the top of the flame they should ignite.

With a small generator like the 4"dia. x 4"long filled with propane or natulal gas and as little air as possible to mix with the gas, would expect the ring to ignite over the candle.