Episode 121: Thermite vs. Ice

Air Date: May 27, 2009

Igniting a bucket full of thermite on top of a several blocks of ice will cause an explosion.

confirmed

Adam and Jamie tested this myth as shown in a viral video (with one galvanized steel bucket full of thermite on top of ten 1-pound/0.45-kilogram blocks of ice). An explosion did indeed occur, thus confirming the myth. Using more thermite and more ice resulted in a larger explosion, enough to literally rain down fire a few seconds afterward and send ice chunks flying over 150 feet (46 m). In a first for the show, however, no explanation was given for why this occurred, because there is none; while hypotheses ranging from the rapid release of hydrogen and oxygen from the vaporizing ice by the thermite to the aerosoling of the thermite itself exist, no one has been able to definitively prove exactly what happens to cause this mixture to be so volatile.

The vibrations caused by a car stereo system at full blast is enough to trigger a misfire in an SKS rifle.

busted

This myth originated from Russian gangs, who use an SKS rifle with a freesliding (as opposed to spring-activated) firing pin. Supposedly, any large vibrations, such as from a loud car stereo system, can cause the firing pin to trigger and fire off round after round at random. To test this, the Build Team “pimped their ride” with the most advanced sound system they could get, and placed several of the appropriate rifles in different areas in the car before subjecting them to several decibel and tone levels worth of sound. However, none of the guns went off. Even taking the guns for testing at a sound studio and getting a custom car specifically designed for sound system contests couldn’t produce a result.

The shock wave caused by an exploding bomb is enough to trigger a misfire in an SKS rifle.

confirmed

The Build Team tested another, similar myth from the same source, involving an exploded bomb setting off guns placed around the blast zone. This time, one of the guns did fire from the shockwave of the explosion.

Holding a hunting revolver improperly can cause your fingers to be blown off by the escaping gasses emitted when the bullets are fired.

confirmed

This myth came to the MythBusters in the form of a picture that was too graphic to show on air. After testing the handgun and noting the power of the gun’s recoil and the gasses that emitted from between the barrel and the chamber, Adam and Jamie built a pair of chicken hands to test the damage these gasses can cause to an unprotected hand. While Jamie’s less anatomically-correct hand only suffered some minor flesh damage from the gasses, Adam’s hand – specifically created to mimic the bone and joint structure of a human hand – had one finger blown almost completely off, confirming the myth.

43 Comments

  1. Fred says:

    Playing with thermite. Now you boys are approaching your destinies.

  2. Will says:

    What is the make and model (caliber) of the handgun used on episode 122?

  3. Ed says:

    Dear Mythbusters,
    With the thermites extreem heat, could the rapid melt of ice to water to steam, with steam being the explosive force? The ice for a split second becomes a sealed contaner and the steam explodes the ice blocks

  4. James says:

    Dear Mythbusters,
    I am currently watching the episode about the SKS weapons being set off by the sound system in a car. Although you did try multiple variances of bass, One thing I didn’t see you try was punch bass. Punch bass is found in most songs, and on Bass cd’s. A couple that you could try is: Bass 305, Atomic 24′s and various others. A lot of these cd’s or MP3′s are used in Bass competitions. The single hard hit of bass, multiple times (punch bass) may be just enough to set off the weapons. Just a thought from someone that deals with stereo’s, tuning, and used to do bass competitions.

    • Anne says:

      Gotta agree with this one. I wondered why they never tried “thumping” as opposed to a steady tone.

  5. Dan says:

    Please confirm the make and model of the chicken finger handgun.. I had my thumb blown in half by a 460 s.w it looked like the same gun.

  6. Angelo says:

    Ed has a grasp on the concept but what he didn’t say was that when you make steam from the thermite at the same time with the intense heat you are splitting at a memcular level to produce the nitrogen and oxygen. I bet if you put a sniffer in the area you would see a higher result than expected. they say it burns at high temp 2887. you have al oxide, iron oxide in powder form this is the same stuff you use in welding. so at 2887 degrees fer. I am asumming complete seperation of atoms of ice in one instance ice becomes steam then splits and becomes pretty much at that temp close to plasma “total heat = large explosion”

  7. Nickesh says:

    The reason the thermite and ice mixture exploded is because the relentless heat of the thermite superheated the ice
    The ice turned from itself into steam instantaneously, with NO liquid state.

    When water is superheated, and it comes into contact with a suface with ANY nucleation sites, it turns into masses of steam.
    The rising steam is what gave the explosion the upward force.
    The particles of the explosion came from the molten iron and aluminium oxide (The products of the thermite reaction) as well as fragments of the metal bucket

    To be honest, I’m surprised you didn’t think of this, it is simple physics, and superheated water is used everyday in coal-driven electricity plants.

  8. Wrex says:

    Nickesh beat me to it, though there is always a liquid state, just so rapid it’s all but undetectable (and a factor in the violent reaction).

    You can see the same result with very cold water, instead of ice. I am also surprised you guys didn’t think to try that.

    It’s like when you try to put out a magnesium fire with water. Violent!

  9. albert says:

    Just to let you know matches are vary powerfull explosiv I blow my right leg clean off at just below the knee with a pipe boom 4th july 1976 it was about ft long 11/2 wide with a vary short fuse a was about 30ft away when shrap metal hit me.I have a Cleg now about 70tho dollar later doing fine love your show I have a cos that could be jamei”s twin.PS Karies fine

  10. Andy says:

    Wrex, it’s not true that there is always a liquid state. The solid can evaporate without a liquid state. The process is called “sublimation”.

  11. Glenn Sloggett says:

    I have seen this effect in a much larger scale.I use to work in an Abrasive plant.The Furnaces melted different materials to make abrasives.The melting materials were around 2000f much lower than thermite.When the furnace runs deep you get a burn out,the material cuts through the steel jacket of the furnace like butter and when it hits the water (the furnace is cooled by water)it results in a rather large explosion.All caused by the super heated material hitting the cold water or concrete.No chemical reaction needed,just hot meets cold BOOM !!!

  12. Tim says:

    hey guys. I was talking to a chem teacher and we hypothosized that the combanation of the thermite, the coating on the galvanized bucket, and the H2O in super heated form caused the explosion. Try it out and see if thats the case.. Have fun AND BE SAFE!!! :-)

  13. Jim says:

    As an engineer in the steel industry, the answer is obvious. Whenever molten metal (steel, aluminum, etc.) engulfs water or ice it will very rapidly flash to steam. The expansion is something like 1400 times for aluminum and most likely more for steel. So, assuming 1 cubic inch of water/ice is engulfed, it would make over 1400 cubic inches of steam. The pressure inside the engulfed water would rise rapidly and be immense and looks just like an explosion from combustion. Anyone in the steel industry has witnessed this event. It isn’t something you forget.

  14. caleb critcher says:

    Has anyone ever dumped ‘fresh ice’ right out of the freezer into a cup of room temp. liquid? The ice pops and cracks. Sometimes it breaks into several pieces. Maybe the sudden extreme change in temperature caused the ice to shatter which threw the thermite into the air. The airborne thermite became particulate which increased the surface area allowing rapid combustion, hence the explosion.

    One more thing. I know the gentlemen that lost the end of his thumb in the revolver accident is suing the manufacturer. Is that why I can’t watch that part of the episode on youtube?

  15. howie0 says:

    i know it is a guys prerogative to wanna blow stuff up sometimes lol. the thermite thing was cool, but it suddenly hit me while watching, what’s more scary, thermite blowing up ice, or ppl just being able to blow up ice with thermite for the sheer fun of it?

  16. Jon says:

    I’ve just seen the show with the SKS and think the rifles that the Ruskies used were older weapons that have been used a lot.

    I have two SKS’s and one have them is now dangerous as it has converted itself from a semi-auto to a fully auto. Loading a round into the chamber can set the weapon off where it will fire three or four rounds before it jams.

    I am ex- British military and have been told by a military friend that the probable cause is a worn sear or sear spring. Maybe this was the case with the Ruskies rifles.

    Please feel free to come to Canada and try mine.

  17. rob says:

    Hi I find it interesting that free floating firing pins would be blamed for SKS firing on their own as M16s M4s C7s and C8s their Canadian variants and other assault riles have similar firing pin configuration as well I would suspect that the myth originated from a misidentification of the weapon I would think it was some for of machine gun that fires from an open bolt configuration i.e. FNs GPMG and MINIMI and PKM are belt fed with the exception of the MINIMI witch can be mag fed too they all fire full auto only. There are many other guns fire in this manor I would be interested to see if one with a damaged or well worn ser could discharge in the manor indicated in the SKS myth as I have seen one fire from a significant impact and it was in good condition so a old Warsaw pact country weapon in poor condition I think could happen plus people are notorious for misidentifying Russian and eastern European guns.

    Thank You

  18. Tom says:

    Hum, could it be possible the thermite flash heats the tiny air bubbles and that is what causes the explosion?

    Tom

  19. Chris says:

    Thermite/ ice: Not sure I buy the hydrogen/oxygen combustion or pressure related ideas, but I do remember that aluminium will burn in water. So it goes like this: the thermite ignites, vaporising the ice and creating a cloud of hot aluminium powder in steam (which then burns fast enough to create the explosion).

  20. David says:

    I wouldn’t consider the SKS “myth” busted just because it didn’t happen to those particular rifles. Some SKS’s have bad sears as a result of poor manufacturing or modification by someone who didn’t know what they were doing. If your SKS has negative hammer-sear engagement, every time the rifle gets bumped, the hammer slides a little along the sear, getting closer to the “breaking” point. Eventually, a bump or vibration will overcome the last bit of friction and the hammer will fall.

    This doesn’t have anything to do with the spring on the firing pin (or lack thereof.) The spring is there to help retract the firing pin after a shot is fired. If the firing pin channel gets gummed up, the firing pin can get stuck in the forward position. When the bolt closes on a new round, the protruding firing pin hits the primer and the gun immediately fires. This is usually the cause of “full-auto” malfunctions and slam-fires, but it won’t cause the hammer to inadvertently fall.

  21. Dan says:

    As caleb critcher said, putting an ice from the freezer in water can cause it to crack, sometimes violently.

    What happened to me: I had a hot bowl of soup, to hot to eat. So I dropped an Ice cube into it. The ice cube “exploded”, into about 5 peices, and I had soup spread about 3 meters away from the bowl!

    So I think it’s about causing stress fractures in the ice to explode.

  22. Paul Malley says:

    SKS Rifle

    The firing rate ( frequency) of the rifle would
    be well within the range of Audio frequencies.

    This would mean that the firing pin is oscillating
    in its housing at that frequency.

    Try attaching the rifle to a parts/materials feeder, these things can shift several hundred
    tons per hour rock if you want a big one, and
    try again!

    Your problem was that you were expecting the air
    to transmit the force.
    The rifle was probably sitting on the car chassis
    effectively hard coupled to the speaker.

  23. Paul Malley says:

    Couple of further points.

    Run the feeder at the same frequency as the rifles
    fire rate.Obvious?

    How far would you have to drop the rifle onto a hard surface for it to self fire?

  24. Glen Hinckley says:

    The gun is the S&W X Frame in .500

    It is a dangerous weapon.

  25. Ffynn Bowen says:

    I am certain that the SKS myth tested was not what happened in the case of the Russian gangsters. I think the Mythbusters went in the ENTIRELY wrong direction with this one.

    Think about this one…

    The dirty Russian gangsters and their(THIS IS VERY IMPORTANT!!!) *DIRTY* rifle, are cruising around with the rifle’s bolt ‘locked’ into the *REARWARD POSITION* and with several cartridges in the magazine. The rifle is sitting with the butt on the floor with the barrel pointed upwards. The pumping soundsystem knocks the bolt out of the rearward position and into battery. BUT WAIT! Because the dirty Russians never cleaned their dirty rifle the floating pin of the SKS is all gummed up with residue, and is stuck in the forward position. When the bolt comes forward… SLAM FIRE!

    This is something that is VERY common in SKS rifles that have not been cleaned in a long time. It is well known in the firearms community that when you release the bolt to chamber a cartridge and a round ignites (slam fire) you need to clean your SKS because the pin is getting stuck in the forward position. This happens because there is no spring to pull the pin back into the housing.

  26. Alexander says:

    Thermite/ Was at me similar without ice and water. Has lighted a magnesian shaving – at burning the firm cover was around formed and inside burnt. Explosion was less. If to add ice begins also as at you. There is a grenade instead of steams and gases as you consider.

    SKS – sniper gangster Simonov (СКС – снайперный карабин Симонова).

  27. Cliff says:

    The comments about the SKS firing pin channel being gummed up are on-track and nearly correct.

    The single most-common reason for an SKS to have a non-intentional discharge is that the firing pin channel is gummed up with cosmoline (a greasy/waxy military-grade preservative. So many of these rifles were made, then stored in military armories, that the majority of the rifles that come into private possession arrive coated inside and out with cosmoline. The new owners typically clean the rifles fairly thoroughly, but frequently neglect to strip the bolt and remove the cosmoline from the firing pin channel. Subsequent incomplete cleanings leave dried-up chunks of cosmoline that can break loose and jam the firing pin in the forward position. Thus, either slamming the bolt home with the firing pin frozen in the forward position, or simply vibrating the spring-loaded bolt (with the firing pin frozen forward) against the primer can cause the cartridge to be ignited.

  28. Ron says:

    The SKS rifle in proper repair isn;t likely to accidentally discharge. The things that wil ltypically make it have an AD are:

    1) Firing pin does not retract when loading a round into the chamber and the rifle slamfires. This is because the pin is jammed forward for any number of cleanliness reasons.

    2) Negative sear engagement. This is NOT common on SKS rifles, but is sometimes found on rifles that were refurbished at verious depots where the workmanship wasn’t great. This isn’t the rifle’s fault, it’s the fault of the person that improperly orked on it.

    3) Soft primers. On every free-floating military rifle, the design intent is to use military ammo with appropriately hard primers. When reloaders sometimes use soft hunting or match grade primers, the inertia of the firing pin can sometimes set off a round when chambering the cartridge.

  29. 97 says:

    i heard there was some sort of thermite and dry ice rocket. that would be cool to see on mythbusters.

  30. My2cents says:

    I’m with the sublimation explanation, but with a few tweaks.

    When the thermite penetrates the bottom of the bucket it is initially as a small jet. Look at the video with the plates and you can see this, it is also why the hole in the plates is so small. This creates a cavity in the ice that the larger mass of thermite can fall into when the bottom of the bucket fails. This both increasing the contact surface between thermite and the ice and supplies a space for the steam pressure to build up in until the inertia of the ice is overcome. The effect is the same as an exploding pressure cooker, just much faster.

    If they want to investigate this further, they could recreate it but put sand in the bucket and different weight charges of black powder in a cavity in the ice until they approximate the thermite on ice explosion.

  31. Dave says:

    I agree that the SKS issue is due solely to a dirty or gritty bolt with a free floating firing pin. As the vibrations increased the pin could “walk up” due to grit to a exposed point that would impact the primer. Slam fires and full auto misfires have occurred with SKS rifles, both Russian and Chinese. Murray’s Gun Company makes a drop in spring loaded firing pin that will alleviate the problem. However, maintaining a weapon and knowing how it functions is something that not everyone does and is aware of. The fact that a round was in the chamber that caused the original misfire just illustrates the stupidity of the person that was involved.

    • Johan says:

      hi
      had an incident once with a r5 rifle that went auto when not supposed too
      found that the owner used civilian 223 ammo{boxer primers} when cocked with military ammo {berdan primers} a small indentation was found on the primer
      seems the boxer primers are more sensitive
      A real danger when used in weapons with floating pins
      My 2 cents worth

  32. Dave says:

    I need to add that the original story was that the rifle was in the back of the car. Misfires can occur on the firing line or anywhere else for that matter.But, there is always a reason why.

  33. jimmie says:

    dear myth busters it would b interesting 4 u guys to do a episode on slam fire guns peferbly in the saturday night special catagory . the weapons in ? should b hipoint 9mm and jimenez 9mm . thanks

  34. Raoul says:

    Greetings!
    The reason for the explosion is the violent change in volume from solid to gas.

    One mol of water has a volume of 22.4 liters.
    One mol of water weighs 18 grams
    Each pound of water (450 grams) equates 450 / 18 = 25 mols and when converted to gas, a volume of 560 liters (= 19.8 cubic feet).
    This, at room temperature… At the reaction temperature, say 1,750 degrees Kelvin this volume increases 5.9 times, with a total of 3,300 liters or 117 cubic feet…!!!
    And this from a pound of water…
    Finally, the explosion comes the violent expansion of the ice –> water –> steam.

    This same principe is used in guns… In a bullet, the powder ignites, freeing an enormous amount of gas that impulses the tip of the bullet through the barrel…

    Elementary, my dear MythBusters…

    Best regards!
    Raoul

  35. RICK says:

    In the Louis F. Garland Fire Academy in San Angelo. TX at Goodfellow AFB we were taught about an explosion much like what some of you have mentioned. It’s called a BLEVE (Boiling liquid expanding vapor explosion ) they can be some of the most destructive of all explosions. Think burning propane tank BOOM ! From a former Army Fire Fighter

  36. Richard says:

    I am skeptical of the confirmation of fingers being blown off:
    1. A chicken’s bones have thinner walls than a human’s and are more brittle.
    2. There need to be tendons and ligaments holding the hand together.
    3. The confirming shot was taken with the thumb in a position that would be very difficult to attain in real life. The position was chosen to maximize the effects of the blast.
    4. The thumb was tied to the barrel of the gun so that there could be no reflex action.

  37. adrian says:

    what audio equipment was used the the car? i know it was all mtx but what amps and speakers where used?

  38. Stu says:

    In the last 5-10 mins of the episode there’s Jamie explaining the effect of the thermite and ice at ten times the quantity of the first test, I was just watching Jamie explain the fuse ignitor which he then fires 3 feet from the bathtub full of thermite while covered in a now red overalls. Was just thinking this is probably not the safest move Ive seen on mythbusters, STAY SAFE JAMIE.

  39. Jake says:

    I believe the SKS explosion myth was also busted. They didn’t check to see if the rifle that went off had dirt in the muzzle. What likely happened is the explosion threw the rifle into the air, and the rifle landed muzzle first; the momentum of the firing pin set the primer off.

    It’s also worth pointing out that there are many other guns designed with free floating firing pins (like the m16 family) which do not have the negative reputation the SKS does. This is likely due to the high amount of cosmoline packed in imported guns combined with people who didn’t bother clean them first before heading to the range.

  40. John says:

    RE-read the wikipedia article, effectively explains as stated above, the rapid expansion of steams carries the super heated substance with it, while certain metals can cause the hydrogen to react, resulting in secondary explosions.
    Remember now I first learned that metal fires cause the hydrogen in water to explode from my father who served on a carrier and watched them push over a fighter that was on fire cause the aluminium was burning.

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