In a petrochemical industry seminar, a guy told about invisible fire (only heat can be felt) he said it’s very dangerous and has a lot of potential for burning. What chemic causes invisible fire? if fire is defined as the chemical reaction that produces heat and light, how is it invisible?
In: Chemistry
The chemical reaction if a fire do not produce light it produce hot material and some will glow in visible light bit not others. Fire or more exactly combustion is a high temperature chemical reaction with a oxidizer, most often oxygen, that is rapid and release energy. It will heat stuff up but by itsefe not produce light. What you mostly see in common fires are hot glowing soot particles.
A fire that burn cleaner that do not produce lots of sooth will be less visible. Look at [https://youtu.be/lPdZmCbbjtM?t=169](https://youtu.be/lPdZmCbbjtM?t=169) where a bunsen burner is adjusted to get the right amount of oxygen and the flame change from bright orange to quite had to see blue. If there is more oxygen the combustion will be more complete and less soot that glow is produced. What is produced is just water and carbon dioxide and at the temperature is reaches it will not emmit visible light to a very high degree.
Look at methanol that burn and do not produce a lot of sooth, the flame very had to see out in daylight [https://www.youtube.com/watch?v=1ZEEuCHdWFA](https://www.youtube.com/watch?v=1ZEEuCHdWFA)
you might be thinking of a Methanol flame, which is less “invisible” than just “very very very very (a few more very’s) pale blue flame – **almost** colourless in daylight, and still a very dim blue in the dark.
[here’s a visual comparison](https://youtu.be/1ZEEuCHdWFA)
The yellow flam you see in fires is mostly sot that is heated until it glows. Other chemicals glow at different colours when heated. For example neon glows bright red which was used in various signs in the past. Some chemicals glows very dimly in the visual spectrum, for example water and carbon dioxide. Water might give out a faint blue light but not as bright as sot does. Carbon dioxide can similarly glow a bit orange but again it is faint. Therefore if you have enough air to a flame and mix it well then it will not form sot and you get a faint flame. This is how you adjust a torch or burner, you increase the amount of air until the flame becomes invisible. Or if you burn a very light fuel like alcohol you do not get any sot and therefore no bright yellow flame. You might see the faint flame in low light conditions but not in daylight.
“Fire” is not an object. It is a chemical reaction, which releases gases and energy. Most of the time, that energy takes the form of both heat and photons in a wavelength you can see.
But there are also other wavelengths of light which you can’t see. That’s what invisible fire creates: it’s not that it *doesn’t* create light, it’s just that you can’t *see* the light it creates. It could be infrared, or (more likely) ultraviolet.
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It quite literally is a flame that emits little or no visible light. You say Fire is a chemical reaction that releases heat, or light, but it realeses energy and gas, which “most” of the time the energy is the heat you are used to, and the energy can be what you see as well.
The energy that is released that you see are photons in a wavelength.
There is something you may have seen called “The Wavelength of Visible Light” now there’s a reason it’s called “Visible Light” as there are plenty of wavelengths of light that are not visible to us. The invisible fire they reference are most likely creating wavelengths of those lights.
They can be talking about the example of invisible fire which is a gas fire. When certain gases burn, such as natural gas or propane, the flames may be nearly invisible or have a very faint blue color. This can make the fire difficult to detect visually, especially in well-lit environments or during daylight.
Other told what if fire. Ill add example.
When hydrogen burns, it is invisible and does not produce smoke. Thus scienties adopted broom test. People poke brooms in front of them to see if they start to burn.
https://www.iflscience.com/the-broom-test-one-of-the-stupidest-things-that-ever-took-place-at-nasa-67319
You know how if you heat up a stove or a piece of metal really hot, it glows? That’s incandescence, when a hot object gives off light that we can see.
In a flame, there can sometimes be tiny bits of material that don’t fully burn up, but get heated up really hot and glow. Multiply this by thousands and thousands of particles, you get a glowing flame.
Now some things when they burn, they burn very efficiently, where there’s almost no leftover particles to glow, but the flame is still there.
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