Explosive Gas Produced by Rust in Confined Spaces

That scenario doesn't sound very believable. Rusty confined spaces tend to be oxygen-deficient, supporting neither respiration nor combustion, much less explosion. You may need to look elsewhere for an explanation of the alleged events.

Just to add to the original post , the bolts that exploded out of their hole were dry , had no grease on them and i used no WD40 or any other lubricant to loosen them.

The only thing inside the hole was dry powdered rust particles.

You did witness this personally? Was there any heating that might increase the air pressure in the hole? You don't indicate how deep the hole is or the dimensions of the bolts or how much they weighed.

On the other hand, I could imagine there might be negative pressure inside the hole if the rusting iron had removed the oxygen and it might cause the bolt to seal against the threads in the hole as it was being removed. Air rushing in when the bolt cleared might produce a "pop", but launching the bolts 40 meters in the air would require more than that I would think.

No heating torch was used. I have probably loosened 100,000's of bolts but only witnessed this twice. I recall heat and numbness in my fingers and bruising from one incident , and it was definitely a loud sharp "crack" not a pop. I had a breaker bar and socket on one of them when it blew , the breaker bar spun around in my hand and the bolt with socket went skyward. I have seen rust produce large forces in other cases , one in mind being a cement silo which weighed about 20 + tons , it had mounting base plates on its 4 legs , the plates were around 130 x 130mm x 10 mm thick , a layer of rust about 5 mm thick had grown under these base plates and bent them , lifting the entire 20 ton silo by the 5 mm thickness of the rust. Is it possible that the bolts being unscrewed caused the rust to be pulverised , releasing oxygen or other gas ?

You describe what I have heard called "pack-out." The rust forms between 2 plates, and can exert huge forces.

It's an interesting topic in itself , If we keep rust prevention coatings out of the topic for now , there will be a huge range of variables affecting the degree of force created ,such as pollution/acid levels in the air , same influences coming from adjacent soil types in the vicinity , man made sources of chemical presence and variations in steel composition. I look forward to finding some formulas for calculating these forces (once I get back to my office ,iPad in the car isn't conducive to good googles)

"My googling so far indicates that rust can produce hydrogen gas"..what more do you want ?? My own googling has not yet produced any gas, but what I can say is: never fart in confined spaces, as it could be prejdudial to your health, sanity and credibility.One old guy working deep in the double-bottoms of a new ship was faintly heard to yell "anyone who takes more than two sniffs is a glutton", and was found only after rigor mortis had set in.

Not only the old man but likely his rescuers too. The double bottoms of ships are definite confined spaces therefore the atmosphere should have been checked prior to entry.

The rescuers get in the mortality because 3 out every 5 confined space deaths are the rescuers. Don't be the untrained or unprepared rescue hero. You might become a dead hero.

Good Luck, Old Salt

read posts # 24 and # 20

they nailed it.

hydrogen probably wasnt present at all.

pyrophoric iron sulphide , produced by sulfur in groundwater in the coalwash plant where the dozer worked , sulfur + H2O wicking up the bolt threads , producing pyrophoric iron , when the bolt is turned it ignites in the blind hole and blows the bolt out once it is wound out of its thread.

What to learn from this ?

test cavities before hot works

check for pyrophoric iron sulphide , in particular in confined spaces where crude oil , ships fuel oil , or ships bilge water has been pumped or stored , or where coal may have been present that could have also leached sulfur into tanks , storage vessels or pipework leading to pyrophoric iron sulphide formation.

If you google for it , there are ways to make the above hazard inert.

Mines are confined space as well as many other confined spaces are not necessarily oxygen deficient; with or without natural or man made ventilation The fact that he is working there means there is sufficient atmosphere too.

Mines and lots of other confined spaces are not oxygen deficient, with or without natural or man made ventilation. Therefore, that should not be a concern. It depends on a lot more than that rust. Balance how much is using oxygen and amount new coming in. If it had been deficient he would not necessarily be here to tell the story.

Until I saw this I have never had any problems with Hydrogen in rusty steel confined spaces. With steel and air the problem is that the steel will oxidize with the oxygen to form rust. The more the rust the lower the oxygen level. Normal air is 21% Oxygen but I have seen it as low as a fraction of a percent when exposed to steel over a long, but not real long, period of time. This is one of the less obvious "silent killers" with confined space.

I suggest using a "hot tap" procedure to make your initial hole or sampling hole into the caisson if possible. If possible, keep the drill bit flooded with water while drilling. If not possible, modify the hot tap apparatus so nitrogen can be used to flood it. One thing to consider is using a ball valve with a drain on it to replace the standard valve. This would allow you to pressurize the hot tap apparatus with nitrogen on the drain port. When hole is completed put the sampling tube of a 4-gas meter in and take your reading. A 5-gas meter with Hydrogen being the 5th gas would be even better. After testing and obtaining results the hot tap can be used to inject a gas to flush the area inside.

Contact the laboratories or tech service dept of steel manufacturing firms. If possible contact the metallurgical dept of a university. If they don't have the immediate answer for you they can tell you where to get it.

Good Luck, Old Salt

Wat it sounds like to me hydrogen embrittlement, that link touches on that subject and explosive nature of it. " Absorbed hydrogen atoms concentrate at minute faults in the iron and create tension which can lead to an explosion-like breaking of the part. This is hydrogen embrittlement."

Here are more links about about hydrogen embrittlement. And it seems to be pretty common with zinc coat/ plated steel.

That's my 2¢ worth

The corrosive gas comes first than the rust. Rust is an indicator that there is probably a potent gas or compound inhibiting corrosion.

Rust is FeO₂ an oxide and stable form at this type of atmosphere.

Rubbish. Fe(OH)2.7H2O, more like.

You have to look at the source of commit #5, then it's self explanatory

The "explosion" is most likely the reaction caused from releasing the stored mechanical energy generated by the loosening procedure and equipment when the bolt(s) rupture/break.

I have seen this occur many times over my life and in a some unfortunate incidents the person operating the removal tool(s) has lost their appendage(s) or their life.

If indeed there were hydrogen gas or other combustible gases in the immediate ambient air space, the explosion would be spread throughout the area and not just contained inside the hole.

I have witnessed excavator "teeth" that weigh over 400 pounds fly for over 100 feet upwards when dislodged from crusher jaws and end up causing severe equipment and/or structural damage.

It would be a good idea to use a scatter-shield and keep all personnel away from the flight path trajectory when removing the bolts in question as sooner or later there will be a serious accident and/or fatality.

If the environment you are in is suspect of explosive gasses I suggest you ask for, obtain, and use an explosive gas sampling meter to check the area before attempting any bolt extraction.

Always err on the safe side of any executed procedure.

Your family and friends want you whole, healthy, and happy.

I'm with you on the stored mechanical energy as the likely culprit. Still have to be careful regardless of the mechanism.

There was no gas in the environment ,this occurred outside a workshop in fresh air One incident was witnessed by a mechanic who was 20 feet away , the noise made my ears ring . And his face went as pale as mine. I am guessing the 40 metres height by the time it took for the bolt and socket to return to earth ( 2-3 seconds) Bolt sizes for the two incidents were 3/4" with a hole depth of about 2" , the other was 1" but I don't remember the hole depth. Both were on earthmoving equipment , first on a bulldozer track frame which was removed from the dozer and inverted on stands , the other was on a grader attachment . I could understand if there had been lubricant on the bolt but they were both dry , both had dry powdered brown rust on them and in the holes. The dozer had worked some of its life in a coal wash plant , but there was no evidence that the bolt had ever been removed since new and there was nothing else in the hole but rust

Stored tension on the bolt would result in an explosive exit when removed. ALSO the friction from extraction could heat the bolt and eject it from a sealed space. I would loosen all the bolts evenly to allow any tension to be released gradually as is done when removing a valve cover on an engine.

It might be remotely possible that thread-locker was used on the bolts in question and the heat from the extraction process generated enough explosive gas to cause ignition.

Some thread-locking compounds are flammable but I have never witnessed any bolt explosions due to their flammability yet.

I am confident the reaction is from stored mechanical energy wherein the bolt is in a heavy bind from a combination of misalignment, applied wrench/socket torque, and corrosion.

Stay safe and keep your distance we do not want anything bad to happen to you or your tool buddies.

Even 1.5 seconds up and 1.5 seconds back down do not equate to 40 meters.

Coal wash plant: there is your answer. Coal contains minute traces of sulfur. The material can then be in contact with moisture and steel to create an acidic residue, that leads to iron releasing hydrogen spontaneously. Hydrogen generated in this way on active, and somewhat active metals (exposed to acidic conditions) can generate extremely high pressures once the environment is effectively sealed. The release of a bolt from said environment should only happen once the remaining thread count has insufficient shear strength to withstand the pressure contained.

The only other explanation has been given as possible galling of threads during removal can produce sufficient heat to pressurize a pocket of air in the dead end of the bolt hole. That explanation and the fact that such bolts will be under "crazy" amounts of tension during removal, makes me believe this could happen as easily as the other circumstance.

I grew up in NYC after WW II. At the time New York was demolishing great quantities of older buildings, many with rivetted skeletons. The practice was to burn the rivet heads off with a torch. I never saw or heard of an injury using this method. I suspect that heating the rivet head relaxed the metal.

"I suspect that heating the rivet head relaxed the metal."

Considering that the rivets were installed when glowing red, and then shrunk as they cooled to hold the beams together, you're pretty much on the mark with that guess, as the head was 'burnt off' the metal was eased into it's 'plastic state' and the slow transition allowed the bolt to release the stored tension slowly as the hot head was pulled into the hole. Not that you'd see it much, the movement is too small and slow to be spotted with the MK I Eyeball, but it happened.

If anyone tried using an angle grinder to 'cut' the head off, Then you would have had some serious 'bullets' flying around.

Hydrogen doesnt seem that likely to me although the list of other candidates doesnt seem to be very long

To liberate hydrogen from water you need a reducing reaction, ie absorption of oxygen, I would have thought that such a reaction woiuld also rob the air under the bolt of oxygen. Hydrogen in an oxygen starved volume that merely escpaes would be more likely to burn rather than explode as it escapes.

Do you use any kind of compounds during installation of the bolt that might warrant investigation?

Brooklyn Union Gas in NYC would run their supervisor's car exhaust into a pipe that needed cutting via a hot drilling fitting to dilute or replace natural gas before cutting the pipe whether they used a torch or a cutting (saw) rig. The practice with weldolets was to weld them to the pipe with the gas in the pipe. Without O2 there was no xburning or explosion.

Excellent post thank you Scary photo in that link too , the battery drill is well and truly toasted This phenomenon needs to be understood and incorporated into Safe work method systems , it can easily take a life. Those counterweights have only a cubic metre of volume , I am planning a safe method to drill in to rusty voids with total capacity around 800 cubic metres that have been sitting for 40 years ..... Not something to take lightly. My intention at this point is to use a through coolant fed drill bit and an air powered drill so I can sample the air. My client initially asked me to "just cut access portals into them with oxy" , that won't be happening until thorough testing is carried out first.

My intention at this point is to use a through coolant fed drill bit and an air powered drill so I can sample the air. My client initially asked me to "just cut access portals into them with oxy" , that won't be happening until thorough testing is carried out first

How about a water jet to cut into the vessels for your air sampling access?

Sometimes I am more conservative than others (this means safe/ty). You should modify your proposed procedure to eliminate more of the unknown or reduce it and it's possibilities. Expanding on #2, do not do anything until you check the atmosphere at the drill site with an LEL meter. Best to use a 5-gas meter with Hydrogen as the fifth gas. Operate it from the time of set-up to well after completion of the task.

Use a hot tap set-up so that you can capture, dilute and exhaust any gases, good or bad, away from the drilled hole. You can't absolutely be sure what is there so get it away from where it can do harm.

If you use an air powered drill use one that has a ported exhaust and use it instead. This will take the exhaust pneumatic power air away where it will not dilute your LEL meter. This permits you to have more accurate readings and you can tell when to shut down when the LEL gets too high. You can always stop, vent and exhaust then resume when the air is good again. Use of a direct exhausting air drill will cause false readings.

In many incidents with the potential for explosions, blast or fires the fatalities are not well known. They usually involve only a couple of people at the most and often are in rural areas. Check the Chemical Safety Board site http://www.csb.gov/ the National Transportation Safety Board http://www.ntsb.gov/investigations/AccidentReports/Pages/pipeline.aspx and the Dept of Transportation, Pipeline and Hazardous Materials Safety Administration http://www.phmsa.dot.gov/pipeline .

Unfortunately the type of work you are describing most often happens at rural natural gas collection pipe lines which bring the gas from the well to collection piping

What you are potentially working with is identical to a natural gas pipeline penetration with a high risk of failure. About the only difference is Natural gas pipelines run at about 1,000 psi.

It is a shame to take the risk of dying from an unprepared for preventable action in any situation. That's what thorough and complete risk analysis is for.

Good Luck, Old Salt

Yes . Good points. I think a mag base air drill with remote operability would be best to keep me safe . if I was only drilling in to one cubic metre my approach would be a little softer however due to the huge volume (800 cubic metres) , any approach must eliminate 100 % explosion risk , any explosive event would decimate hundreds of metres around and destroy the structure. Not something to take lightly.

From a slightly different angle to previous answers, I assume that some sort of 'gas pressure' builds up in the hole and is enough to eject the bolt as it is unscrewed. I have no answers other than to 'guess' it could be H2 or CO. Either being present due to O2 depletion due to rusting, and then the lack of O2 forms CO with the carbon in the steel, or H2 from the loss of O2 from water. This would need a source of ignition to be explosive.

But if there is no ignition can this type of chemical reaction produce an increase in pressure without heat - and bearing in mind a gradual release of the bolt from a blind hole would rapidly reduce any pressure - so it would have to be very high to start with if there is enough pressure left to eject the bolt when nearly undone. Especially as suggested elsewhere, there is enough pressure to also cause personal injury.

I am curious myself. Until this post, I have never heard of exploding bolts, but depletion of O2 of the air in steel vessels is well known.

Great Question and Sharp attention to detail. Magnetics control most everything that we humans do or see and your EXPLOSION that you witnessed was a REALITY and much more common then you would ever guess! Yes l am going to the Molecular and even the Atomic levels here but that is where the danger that you face STARTS! I cannot stress this enough, THIS IS A VERY REAL AND DANGEROUS SITUATION MADE FOR YOU BY POOR EQUIPMENT DESIGN. RUST/IRON OXIDE AND HYDROGEN DO NOT PLAY NICE AT ALL. H BONDING IS VERY POWERFUL AND YOU HAVE AN UNLIMITED SUPPLY THAT SURROUNDS YOU DAILY IN AIR WITH HUMIDITY OR WATER H2O. Simply, You cannot keep "AIR" out of anything except maybe tightly controlled lab experimrments with very expensive equipment! There is your H supply. Might take a tad longer but weather WINS! The only ? I have is was this "Box" installed over a PAINTED SURFACE OR BARE METAL? Painted is my guess bc paint has enough garbage in the base ingredients ie Sulfur, and Metals to easily finish off a pyrophoric state with the H! The Coal mines are NO BRAINERS AND HUNDREDS OF TIMES MORE DANGEROUS DUE TO THE NATURAL AMOUNT OF SULFUR IN COAL. SULFUR ADDS A VERY WELL KNOWN PYROPHORIC TENDENCY TO H, O, and C!! The S is Diamagnetic or - Negatively Charged, similar to the PH scale in that the opposite or +, BASIC, and -, ACIDIC CHARGES ARE MAGNETIC IN NATURE. WHILE THE S has the second lowest or negative charges for the ELEMENTS AND COMMON INORGANIC COMPOUNDS. IRON (+~14,000) and POSITIVELY CHARGED SO MUCH THAT IT IS A "FERRO" Magnetic Charge. Paramagnetic charges are positive and Temperature plays a large part! IS THE POLAR OPPOSITE TO S (-45 to -60), MOST HYDROGEN MOLECULES ARE (-20 to -30) Diamegnetic Charge, O (+10,200)! Paramagnetic Charge. Hopefully you can see the opposites attract part of magnetism. However, the Diamagnetic Charges are the real power brokers and most always win out. Dont let the lower numbers fool you. An Iron field nice and rusty, when mixed with H or S, S is like mixing 99% Sulfuric Acid and a Pure Sodium Hydroxide Salt crystal. The Sulfuric has a PH of 0 ZERO, and the NaOH has the POLAR OPPOSITE PH OF 14 with 7 being Neutral. PLEASE NEVER EVER DO THIS AS IT WILL EXPLODE, NOT NEUTRALIZE EACH OTHER!!..Both compounds are VERY EXOTHERMIC IN NATURE, NO NEED TO GO THERE. THAT IN A LONG WINDED NUTSHELL IS WHAT YOU HAVE SEEN. MOST PHD's will say that you cannot have Diamagnets on EARTH, then talk in a mile of circles trying to explain something they forgot from day one in Chemistry. If you have seen magnetic levitation experiments?!...THERE YOU GO...Diamagnetism. If you will type diamag... Into Wikipedia, that is the easiest read and understand for ALL MAGNETIC STATES! Be sure to make copies and click on the link that reads "Magnetic susceptibility of the Elements and Inorganic Compounds" for a very complete chart of the applicable charges for each Element and IO Compound. This chart made it very easy to see the overall picture at once and certainly was the key in me understanding and then using these theories in everyday Industrial Maintenance situations as I have sold Industrial Maintenance Chemicals for 25 years as well as maintained 3 fully equipped Labs for some creative inventing. Its better than watching TV TO ME!! The wrap up final answer for you is that Magnetism is the CORE ISSUE AT HAND. YOU CANNOT REALLY DO MUCH OF ANYTHING TO CONTROL MOTHER NATURE, however, IF YOU RESPECT THE POWER AND DANGER AT HAND AND TREAT EVERY SITUATION AS IT COULD BE THE LAST ONE WITH A WRONG MOVE, GUESS WHAT, YOU WIN !!...That eliminated, I would say a good 90% OF THE POTENTIAL FOR BEING SERIOUSLY HARMED BY SIMPLY BEING AWARE AND EDUCATED OF THE DANGERS. TRUST ME WHEN I SAY THAT THOSE BOLTS WERE MOST LIKELY RUSTED FROM ONE SIDE AND STRAIGHT THROUGH THE METAL BC OF THE POOR METALLIC IMPORTED NUTS AND BOLTS. PLENTY OF SPACE FOR H TO OVER EXIST, THEN THE CATALYST IS THE HEAT FROM THE METAL TO METAL CONTACT FROM TURNING THE BOLTS WOULD EASILY INGNITE WHATS LEFT AND FULLY REACTED WITH THE H...EASY EXPLOSION AND VERY VIOLENT AT THAT. PLEASE BE VERY, VERY CAREFUL IN THE FUTURE WHILE WORKING SIR!!...SAFETY FIRST ALWAYS!! I hope that somehow, I have been of help to you today. Have a GREAT REST OF THE DAY!!

You may have it there . The dozer did work in a coal wash plant , so if Sulfur got in to the bolt threads then that combined with hydrogen and small sparks as the rusty bolt was unscrewed would be the culprit . Perfect storm . Lucky for me that I was using a 24" long breaker bar to unscrew the bolt , reckon that gave my head around 12 inches of survival room as the bolt shot past me . �� Beautiful post

How would coal dust get into the thread to provide the sulfur if the tolerance is so tight that hydrogen can't get out. Even if the hydrogen is in the form of Hydrogen sulfide surely this is stretching things a bit.

At one power station that I dismantled they had large Hydrogen cylinders for generator cooling. The bottles were empty because the hydrogen just leaked away. It is terrible stuff to try and store.

Why would it stay put in a thread?

BAB

why would the hydrogen stay contained underneath a bolt ?

i dont know , at a guess maybe it was captive due to a seal of rust around the head of the bolt.

how did the sulfur get into the threads ? maybe the same way that water / moisture did that caused the rust.

The rust was all the way down the threads and in the base of the hole , so if water had sulfur in solution , then capillary action or wicking carried both water and sulfur down the threads to the base of the hole , then over time the pyrophoric rust formed.

When the bolt was cracked it only locked up tight around half way out the hole , so my presumption is the rust being pulverised in the threads caused a spark at that point igniting whatever gases were present at that point and bingo , we had a bomb in a bag.

all facts considered , i think this is the most plausible cause.

I am not trying to disagree with you. It sort of makes sense. It is just that hydrogen is such skinny stuff that it is dam hard to store even when you are trying to design a proper storage container.

It is Harry Houdini on steroids without the bulk and with a grease job.

BAB

My two cent theory: Rust resulted in hydrogen gas in the hole but no oxygen.

As the bolt was unscrewed the vacuum pulled air into the hole raising the oxygen level giving a flammable mixture.

Heat and friction as a result of extracting the bolt caused a build up of static electricity between the rusty bolt and the threaded hole.

As the bolt was separated from the hole a static spark ignited the flammable mixture. Perfect storm conditions.

"when the thread was disengaged there was a sharp explosion"

to JustCurious #21

Knowing nothing of the problem of exploding bolts¹ before the OP raised the question - and reading all the replies - what you say makes sense to me.

1) PS to my previous post #19: To say I have not heard of exploding bolts is not strictly true. I have heard of them - those that are designed for the purpose.

It was the OP's problem with bolts that were not meant to explode that I have not heard of.

If your theory is correct then what is to be done about it?

Suggest testing under safe controlled conditions.

Try small amounts both pyrophoric iron powder and hydrogen gas in a simulated conditions to recreate a small explosion then see if it can be mitigated using the CO2/argon gas from a mig welder to wash over the area.

If this works then do this while turning the bolt out. This should keep oxygen away till bolt is out completely.

Stress and strain permitting, a small hole along the bolts or a small hole into the blind hole will prevent pressure build-up.

But I find it hard to believe that the problem experienced by the OP is the first time it has happened. The solid mass of information by Paul G #20 suggests the problem should be well known by engineers who move in these circles - so what do they do to prevent this problem.

Yes. Agreed . See post by Godfrey above . "Not all rusts are the same" Now we have a name for it. Reading through all the posts above , it appears that pyrophoric iron is not well known so I am glad I started this thread. Thank you kindly

GA for post 24 above , I have never heard of pyrophoric iron sulphide yet considering how commonly it could occur I am amazed it is not taught more in educational environments.

how many ships have been suddenly sunk due to pyro in fuel oil tanks ?

that stuff can be very high in sulphur ☹️

Posts 15 , 20 and 24 are the winners on this topic. Who is going to share this thread with their OHS department ? Have a safe day folks. :)

funny how the most accurate answer in the whole thread is barely noticed and didnt get the GA's that it should have

When I was a kid in high school chem lab we heated S and Fe dust in a test tube and then smashed the test tube outside and it ignited like a sparkler on July 4th

Nice!

I am now retired - living in FL - space coast - and sparklers are illegal here - what a shame for the kids - most of them are playing Pokemon Go. But I am just an old f**k - what do I know. I should have been a rap star.

I have often thought that (1) parents need to closely supervise their children to prevent injury, and (2) allow the kids enough liberty to experience life without "the cacoon".

Sparklers seem pretty innocuous compared to adults leaving toddlers in a hot car. Heard we lost a child the other day (I think in Florida) to just such an event. Horrible, preventable loss. I think parents that do that should face at least involuntary manslaughter charges, and if special circumstances are found, up to 2nd degree or 1st degree murder charges.

"Sparklers seem pretty innocuous compared to adults leaving toddlers in a hot car."

While that comparison is valid, it is a bit skewed; it's akin to saying 'giving a toddler a pen knife to play with is pretty innocuous to tossing a toddler in a wood chipper.'

Sparkers are 'mostly safe' as long as the kid is old enough to understand and obey one critical rule:

The Sparkler is @#$%#ING HOT⁽¹⁾ when it's sparkling! Do NOT touch the sparkling bit, do NOT touch the wire left behind as the sparkler burns down, do NOT hold it above, below, or near any part of your body, do NOT stare right at the sparkling bit, and if you even THINK of bringing the sparkler close to anyone else, it WILL be slapped out of your hand so fast you'll think you've been beaten⁽²⁾.

Notes:

1. Pardon my french, but A) kids may not understand how hot 'over a thousand degrees' really is, and B) if their ears are too young and sensitive for strong language, they're too young to be trusted with a sparkler.
2. I do not consider corporal punishment a suitable child-rearing technique (If you DO consider it appropriate, I'm not here to argue), however, when it comes to safety, I will take the option where someone has to deal with some temporary pain over someone having to deal with a permanent injury every time. Little Suzy's hand will stop stinging after a few moments, but if she had burned out Timmy's eye with that sparkler, it don't grow back. Once the crying's done, (and Susy's mom stops giving me death glares) then I can apologize to Suzy and explain to her that I did it to protect Timmy.

I totally agree. Children still need to learn (somehow without being injured) about hot, cold, very hot, dangerously hot, and extremely cold. On the farm, we pretty much came this naturally over time, and were allowed to have firecrackers, sparklers, etc. No one's eye got put out on our place, because we knew if we did something stupid to the other kiddo, our Daddy would blister our behind with his belt. That is just how it was. It worked.

Some parents apparently should be having their backsides blistered with a belt, since they do not get it at all when it comes to their children's safety. Belt beating, caning, or life behind bars, I would take the belt.

We used to make our own black powder for our model rocket engines we were trying to make also, and other than a few blisters from handling a spent engine while it was still hot, no problems. We had BB gun wars, and no one shot their eye (or their buddy's eye out), although one of my buddies shot me in the butt with his replica .45 ACP 1911 style BB gun, and I picked up a caliche' rock and chunked it at him, and chipped one of his front teeth really badly. Stuff happens.

I tend to go along with Just Curious as to the cause. Auto companies were experimenting with the use of steel wool and water vapor and heat to produce H2 for use in producing H2 fuel. In this case, however, we have bits of steel flaking off as rust, H2 remaining in the bottom of the hole possibly from dampness during the original installation (the O2 molecule being consumed to form rust), heat from friction in removing the bolt (as pointed out external heat sometimes applied). So when the H2 escapes and ignites, the heat, present water vapor and steel flakes react to produce more H2 and the reaction becomes larger.