Could Sub-Aural Frequencies Be Used To Start A Fire?

[JCAxe]

Hey,

 

I'm a fiction writer, and I'm currently working on a new book. 

I was wondering if -for the sake of argument- it might be possible for a sub-aural frequency to -if applied to some material- actually combust the material?

 

I'm not looking for specific materials, I just want to know if it would be theoretically possible. If so, what sort of Db would have to be emitted for this to work?

 

Any help would be appreciated,

 

Kind regards,

 

JC Axe

[exchemist]

Hey,

 

I'm a fiction writer, and I'm currently working on a new book. 

I was wondering if -for the sake of argument- it might be possible for a sub-aural frequency to -if applied to some material- actually combust the material?

 

I'm not looking for specific materials, I just want to know if it would be theoretically possible. If so, what sort of Db would have to be emitted for this to work?

 

Any help would be appreciated,

 

Kind regards,

 

JC Axe

No, I don't think so. I would think that starting a fire by any form of sound waves is practically impossible, regardless of the frequency. The amount of power it is practical to transfer via sound waves is just not sufficient. I should imagine that the sheer size of the transmitter needed for very low frequency sound would make this even harder than at higher frequencies. 

 

In fact, researching this a bit, it seems that on the contrary, one can use sound to put out a fire! https://www.scientificamerican.com/article/when-fire-strikes-stop-drop-and-sing/

 

Perhaps you could work that into a story. :)

Edited March 22, 2018 by exchemist

[JCAxe]

Thanks for your reply. 

What about as a trigger to detonate a (crude) bomb.

Ideally I'm trying to think of some sort of scenario wherein the playing of a particular sound could lead to the detonation of a nearby explosive; maybe not directly, as suggested before (in that the frequency itself ignites the explosive), but as a trigger.

I'm wondering if it would be possible, without the physics of it being overly-complicated; the technology involved would have to be relatively simple.

[exchemist]

Thanks for your reply. 

What about as a trigger to detonate a (crude) bomb.

Ideally I'm trying to think of some sort of scenario wherein the playing of a particular sound could lead to the detonation of a nearby explosive; maybe not directly, as suggested before (in that the frequency itself ignites the explosive), but as a trigger.

I'm wondering if it would be possible, without the physics of it being overly-complicated; the technology involved would have to be relatively simple.

Well it does remind me of a schoolboy prank one of my friends told me of, when we studied chemistry together at Oxford. In their final week at school, he and some schoolfriends managed to make either picric acid (trinitrophenol) or nitrogen tri-iodide (I forget which it was) and paint it onto the felt hammer of one of the piano keys in the school hall. The idea was that the school song would be sung at the final assembly and they had found that in the bridging passage between the two verses, there was one key that would struck only during this passage. So they soaked this one hammer felt in the explosive.

 

He told me it worked a treat. Everyone sang as usual and then, during the bridging passage, there was a loud bang, amplified by the sound board of the piano, accompanied by an emergence of a cloud of dust from within, followed by a nervous silence, after which the pianist hesitantly resumed.   

 

Nitrogen tri-iodide is sensitive enough to be set off by sound I think, but it would not be sensitive to a particular frequency. I cannot think of any explosive that would be that selective.

 

I'm sure an electronics engineer could build a circuit that would produce a signal only if one specific frequency of sound were detected. That signal could be used to activate an electrically triggered detonator. 

[DaveC426913]

Of course. Nitroglycerin is a very unstable molecule containing a lot of chemical energy. A sufficient jolt will cause it to reorganize its molecules into a lower-energy, more pleasing, arrangement.

 

Unfortunately for anyone nearby, that new arrangement is in the form of gases with lots of kinetic energy and so want to expand very rapidly. This results in an any bystanders being reorganized into less pleasing arrangements.

 

A sufficiently strong shock wave, such as a subsonic pulse, could conceivably trigger it.

Edited May 9, 2018 by DaveC426913

[DaveC426913]

And by the way, it is a well-known fact that there is only note that will trigger an explosion.
 
 

[JMJones0424]

If we observe that sound is an oscillation of a medium, then we can determine whether or not an oscillation of a medium is capable of igniting a material.  I don't think this is the case. Combustion requires heat, fuel, and an oxidizing agent.  I can't imagine how sound could be used to provide the necessary heat at any frequency or decibel level.

 

Perhaps you would be better off abandoning the idea of sound and instead embrace focused light.  A laser beam, which consists of one frequency of light that is very well focused, could easily produce the heat required to start combustion.  Failing this, one can start a fire with a magnifying glass and a bit of patience on a sunny day.  I don't know that it's possible to start a fire via sound, as there simply isn't enough energy transfer to impart enough heat to initiate combustion without shaking the target to bits.  When increasing intensity of sound, the compression waves would be so significant that heat would be the least of your worries.  At a high enough level, the compression waves would shake apart whatever it is you are trying to ignite.

 

If it is your desire to use sound, which is repetitive compression waves through a medium, to initiate an explosion, then the question then becomes what explosive material are you trying to detonate?  This is not at all the same thing as ignition, though.

[exchemist]

If we observe that sound is an oscillation of a medium, then we can determine whether or not an oscillation of a medium is capable of igniting a material.  I don't think this is the case. Combustion requires heat, fuel, and an oxidizing agent.  I can't imagine how sound could be used to provide the necessary heat at any frequency or decibel level.

 

Perhaps you would be better off abandoning the idea of sound and instead embrace focused light.  A laser beam, which consists of one frequency of light that is very well focused, could easily produce the heat required to start combustion.  Failing this, one can start a fire with a magnifying glass and a bit of patience on a sunny day.  I don't know that it's possible to start a fire via sound, as there simply isn't enough energy transfer to impart enough heat to initiate combustion without shaking the target to bits.  When increasing intensity of sound, the compression waves would be so significant that heat would be the least of your worries.  At a high enough level, the compression waves would shake apart whatever it is you are trying to ignite.

 

If it is your desire to use sound, which is repetitive compression waves through a medium, to initiate an explosion, then the question then becomes what explosive material are you trying to detonate?  This is not at all the same thing as ignition, though.

Indeed, which is why I mentioned Nitrogen tri-iodide earlier on thread: one of the very few things I can think of that could possibly be detonated by sound.  

[JMJones0424]

Detonation is not ignition or combustion.

 

In many cases, detonation can prevent or stop combustion.  As the OP requested " it might be possible for a sub-aural frequency to -if applied to some material- actually combust the material?" I find no reason to conclude that such a thing is possible, but my knowledge is limited.

 

One of the many things that bothers me about modern-day blockbuster action movies is that explosion does not equal fire.  In many cases, explosions put out fires.

 

Detonation is the initiation of a compression wave, and can be reasonably viewed as similar to a really freaking loud sound.  Ignition is the initiation of combustion, which can be viewed as similar to striking a match.  The two are fundamentally different outside of Hollywood.  They have nothing to do with each other.

Edited May 19, 2018 by JMJones0424

[Zoomboi]

As for triggering an explosive, if there is a sound sensor on the bomb, you could program it to react to any frequency or wave shape you want it to.