Dry Rice as a Flame Suppressor?

Do you literally mean "rice" the grain, or "dry ice" ? Your question mentions both. Was this a typo or "term of art". (like "lox" = liquid oxygen, in the James Bond movie.)

Rice... as in Rice, small grains we eat to fill our gullets. I don't recall mentioning Dry Ice

And to be more specific, the specific Gas he Demonstrated this with was...(que dramatic music, followed by Dun! Dun! Dun!) HHO.

How does dry (un-cooked) white Rice stop flame spread of HHO?

Good thing I'm not a cat, cause I'm full of curiosity.

RVZ717,

Since production Flash suppressors are basically Sintered metalic blocks, It makes sence that the Rice would work.

At least for a couple of times. The Metalic blocks fail by fusing into a block to stop gas flow in extreme cases.

With Rice, I would expect that after a couple of hits the rice may itself start to burn and cause further problems.

In either case for the short term and for demonstraition purposes they would work the same way. They disrupt the wave front of the flame and break it down.
This in turn reduces the temperature.

Once the temperature drops and oxygen becomes unavailable due to the run length the flame itself dies.

Flashback now Prevented.

Regards,
Sapper.

Thank you for the response.

This particular setup was made of a homemade torch-head hooked up to a cavity full of (either dry white rice, sintered bronze, or nothing) material. When hooked up with "nothing" as the filler material, an immediate flashback and boom situation occurred (as would be expected). When fitted with the bronze, the torch would stay lit for a while (~20-30 mins) before flashing back (due to drying out). When The Dry uncooked white rice was used, the torch would stay lit for hours with no flashbacks at all. Upon later inspection i noticed (as would be expected) Discoloration (darkening due to heat) of a few (~3-4) individual rice grains, which were located right near the tip.

This just struck me as interesting. For this presentation, the rice worked better than the sintered bronze. The setup produced a 5-6 inch flame capable of slicing through stainless from the tip of the torch (when not exploding the safety bubbler.)

Once the temperature drops and oxygen becomes unavailable due to the run length the flame itself dies.

One extra note: Sinse the gas used was HHO It contains its own oxygen to burn, so this situation is no doubt different than most where the gas needs to have contact with oxygen to burn.

This is an odd thing - dry rice as an organic substance will be combustible so it could be absorbing energy by combustion it could also be working as an insulator. The action could be physical rather than chemical just like the gauze on a Davies Lamp.

What do you mean by the gas being HHO? That is water!

Don't know much about this but if insulation and permeability be a factor try expanded vermiculite (non-combustible)

Yes HHO is the product when water is subject to electrolysis. The gas is popular among the Stan Meyer Hydrogen generator scammers. Its extremely volatile/explosivo! Because it contains it's own oxygen for combustion. also called "browns gas"

Flame suppression is enhanched by release of anti oxidation/inert gases like nitrogen,co2 etc.If rice is found suppressing flame,it could be due to the formation of reducing sugars/glucose formation at temperatures,by possible release of hydrogen/a formation of reducing atmosphere which can suppress flame.This is possible on fact that rice is a starch based product.Is it agreed?

Added to my earlier comment, it is worth noting that starch has hydroxyl[OH}groups,which can produce water with hydrogen at elevated temperatures.

All organic substances can follow the route C_xH_xO_{x ⁺} O₂ -> CO + H₂O + O₂ -> CO₂ + H₂O and CO is highly flammable. Probably with small quantities you are OK but I always worry about combustibles and fires. That is what I get paid for.

It could be the physical shape rather than the chemical composition which is the factor.

Remember that flour (rice or other) is prone to dust explosions - but that would be in quantities. Try and find something similar to rice in form but non combustible. e.g. vermiculite or crushed pumice.

I suspect you are seeing the same effect that a flame arrestor uses. In a flame arrestor there are multiple screens. As the gas passes through the small openings it expands through the openings.

I have heard two explanations:

1. The gas velocity through the small openings is faster than the flame speed for that gas mixture at that temperature and pressure preventing the flame front from passing upstream. Typically the sonic velocity for the gas mixture under those very small openings.

2. The cooling effect of the gas as it expands through the tiny openings is enough lower the temperature of the gas mixture below the (flame) activation temperature.

I have seen a pipe carrying a flammable gas ignite and burn back to a flame arrester. The pipe was glowing cherry red all the way back to the arrestor and the pipe immediately upstream of the arrestor was cool to the touch! The upstream pressure was 10-12 inches water column and atmospheric downstream. (It does not need much pressure differential to work.

I would suspect that your device would work until the chamber the rice is in gets hot and starts to degrade the rice.

It could prevent a flame getting back to a larger (explosive) container.

For the very ignorant among your readers, who haven't much of an idea what the hell you're talking about, could you direct us to some graphic images or diagrams ? Thanks.

Will these people stop at nothing to sell rice?