To the average person, walking into a flour- or sawmill and seeing dust swirling around is unlikely to evoke much of a response, but those in the know are quite likely to bolt for the nearest exit at this harrowing sight. For as harmless as a fine cloud of flour, sawdust or even coffee creamer may appear, each of these have the potential for a massive conflagration and even an earth-shattering detonation.
As for the ‘why’, the answer can be found in for example the working principle behind an internal combustion engine. While a puddle of gasoline is definitely flammable, the only thing that actually burns is the evaporated gaseous form above the liquid, ergo it’s a relatively slow process; in order to make petrol combust, it needs to be mixed in the right air-fuel ratio. If this mixture is then exposed to a spark, the fuel will nearly instantly burn, causing a detonation due to the sudden release of energy.
Similarly, flour, sawdust, and many other substances in powder form will burn gradually if a certain transition interface is maintained. A bucket of sawdust burns slowly, but if you create a sawdust cloud, it might just blow up the room.
This raises the questions of how to recognize this danger and what to do about it.
Welcome To The Chemical Safety Board
In an industrial setting, people will generally acknowledge that oil refineries and chemical plants are dangerous and can occasionally go boom in rather violent ways. More surprising is that something as seemingly innocuous as a sugar refinery and packing plant can go from a light sprinkling of sugar dust to a violent and lethal explosion within a second. This is however what happened in 2008 at the Georgia Imperial Sugar refinery, which killed fourteen and injured thirty-six. During this disaster, a primary and multiple secondary explosions ripped through the building, completely destroying it.
As described in the US Chemical Safety Board (USCSB) report with accompanying summary video (embedded below), the biggest cause was a lack of ventilation and cleaning that allowed for a build-up of sugar dust, with an ignition source, likely an overheated bearing, setting off the primary explosion. This explosion then found subsequent fuel to ignite elsewhere in the building, setting off a chain reaction.
What is striking is just how simple and straightforward both the build-up towards the disaster and the means to prevent it were. Even without knowing the exact air-fuel ratio for the fuel in question, there are only two points on the scale where you have a mixture that will not violently explode in the presence of an ignition source.
These are either a heavily saturated solution — too much fuel, not enough air — or the inverse. Essentially, if the dust-collection systems at the Imperial Sugar plant had been up to the task, and expanded to all relevant areas, the possibility of an ignition event would have likely been reduced to zero.
Things Like To Burn
In the context of dust explosions, it’s somewhat discomforting to realize just how many things around us are rather excellent sources of fuel. The aforementioned sugar, for example, is a carbohydrate (Cm(H2O)n). This chemical group also includes cellulose, which is a major part of wood dust, explaining why reducing dust levels in a woodworking shop is about much more than just keeping one’s lungs happy. Nobody wants their backyard woodworking shop to turn into a mini-Imperial Sugar ground zero, after all.
Carbohydrates aren’t far off from hydrocarbons, which includes our old friend petrol, as well as methane (CH4), butane (C4H10), etc., which are all delightfully combustible. All that the carbohydrates have in addition to carbon and hydrogen atoms are a lot of oxygen atoms, which is an interesting addition in the context of them being potential fuel sources. It incidentally also illustrates how important carbon is for life on this planet since its forms the literal backbone of its molecules.
Although one might conclude from this that only something which is a carbohydrate or hydrocarbon is highly flammable, there’s a whole other world out there of things that can burn. Case in point: metals.
Lit Metals
On December 9, 2010, workers were busy at the New Cumberland AL Solutions titanium plant in West Virginia, processing titanium powder. At this facility, scrap titanium and zirconium were milled and blended into a powder that got pressed into discs. Per the report, a malfunction inside one blender created a heat source that ignited the metal powder, killing three employees and injuring one contractor. As it turns out, no dust control methods were installed at the plant, allowing for uncontrolled dust build-up.
As pointed out in the USCSB report, both titanium and zirconium will readily ignite in particulate form, with zirconium capable of auto-igniting in air at room temperature. This is why the milling step at AL Solutions took place submerged in water. After ignition, titanium and zirconium require a Class D fire extinguisher, but it’s generally recommended to let large metal fires burn out by themselves. Using water on larger titanium fires can produce hydrogen, leading conceivably to even worse explosions.
The phenomenon of metal fires is probably best known from thermite. This is a mixture of a metal powder and a metal oxide. After ignited by an initial source of heat, the redox process becomes self-sustaining, providing the fuel, oxygen, and heat. While generally iron(III) oxide and aluminium are used, many more metals and metal oxides can be combined, including a copper oxide for a very rapid burn.
While thermite is intentionally kept as a powder, and often in some kind of container to create a molten phase that sustains itself, it shouldn’t be hard to imagine what happens if the metal is ground into a fine powder, distributed as a fine dust cloud in a confined room and exposed to an ignition source. At that point the differences between carbohydrates, hydrocarbons and metals become mostly academic to any survivors of the resulting inferno.
Preventing Dust Explosions
As should be quite obvious at this point, there’s no real way to fight a dust explosion, only to prevent it. Proper ventilation, preventing dust from building up and having active dust extraction in place where possible are about the most minimal precautions one should take. Complacency as happened at the Imperial Sugar plant merely invites disaster: if you can see the dust build-up on surfaces & dust in the air, you’re already at least at DEFCON 2.
A demonstration of how easy it is to create a solid dust explosion came from the Mythbusters back in 2008 when they tested the ‘sawdust cannon’ myth. This involved blowing sawdust into a cloud and igniting it with a flare, creating a massive fireball. After nearly getting their facial hair singed off with this roaring success, they then tried the same with non-dairy coffee creamer, which created an even more massive fireball.
Fortunately the Mythbusters build team was supervised by adults on the bomb range for these experiments, as it shows just how incredibly dangerous dust explosions can be. Even out in the open on a secure bomb range, never mind in an enclosed space, as hundreds have found out over the decades in the US alone. One only has to look at the USCSB’s dust explosions statistics to learn to respect the dangers a bit more.
Fun fact: powdered eggs were used in the formulation of pykrete as a binding agent. The duck proteins contained in egg yolk help improve the structural integrity and cohesion of ice and sawdust mixture. While it made this super-pykrete more resilient to cracking, egg dust also made it explosive. That’s one of the main reasons why pykrete aircraft carrier never became a thing.
Great story, but this sounds very unlikely as the egg dust would not be explosive once in the pykrete – it’s a dust cloud that’s explosive, not powders mixed in ice.
Also there’s other much more sensible reasons the pykrete aircraft carrier never happened.
Duck eggs? Sounds like a lie.
I can think of several other reasons why a pykrete aircraft carrier never became a thing that have nothing to do with exploding eggs. Also this would not make the finished pykrete explosive… at all. Did you miss the part where it has to be dispersed thinly in a gas containing oxygen?
An aggressive shake of non-dairy creamer over the campfire is always sure to please a crowd of little boys. Just make sure you and your arm aren’t flammable and that you don’t mind having an asymmetric distribution of hair on your arms.
Solo Cup full in a half throw high arc is a much better plan.
Big fire, so the kids are sitting far back already.
You are doing God’s work, passing pyromania to next generation.
My dad’s gone, but I still remember him telling me:
‘No! I won’t give you fuming nitric acid.’
‘Go to the reloading isle at the gun store’
‘With an 18 year old friend.’
‘Don’t use fake ID, this isn’t 3.2 beer.’
Alternative:
Lite candle at bottom of stair well, wedge doors shut so nobody walks in.
Go to top, throw same cup of dry powder into air.
Leave.
The 2015 Bosley Mill explosion in the UK, caused by wood dust: https://dustsafetyscience.com/a-dark-day-in-cheshire-bosley-mill-explosion/
This reminds me, did anyone ever figure out why thermite will become violently explosive when mixed with water ice, but not with liquid water or dry ice? I know it gets bad when aerosolized (for an example, look up the video where Colin Furze shot some into an old front loading dryer), but the ice mixture always seems to be worse.
Got to be the aluminum powder doing the sodium/potassium thing.
They looked for it in industrial processes w molten aluminum.
Generally not found, just old fashioned steam explosions.
It’s a handy thing to know…Thermite isn’t just the ‘sparkler of illegal fireworks’.
If that were true you would expect it to happen in liquid water as well
hmm, maybe liquid water forms a tiny passivating hydrogen layer, which is pushed through by the ice particles? Definitely needs more investigation.
Dry ice doesn’t contain as much hydrogen as water ice.
You’d expect it to…
Devil is always in the details.
Frozen water does many really really weird things.
Mostly in the process of freezing (e.g. buttloads of electric charge collects on snowflakes as they are freezing.)
Quantum weirdness in small ice bits.
Still good to know…
I would suspect that the electric charge on snowflakes is (naively) more likely to be from falling than freezing?
It’s imperfectly reproduceable in the lab, still anomalous.
I suspect the weirdness in freezing is just better studied then thawing weirdness.
I like the USCSB YT channel. I do not like that a former employers name is in a lot of the titles…
The dust piled up everywhere becomes the secondary explosion. The first explosion violently disburses that into the air, creating the second and more massive dust cloud along with the already hot atmosphere. This chain reaction continues until all fuel source and life is exhausted.
This happened to a grain tower in the middle of the town where I spent much of my childhood, and blew massive chunks of concrete all over downtown. They listed several people as missing because they found no body parts at all.
I’m told, but don’t know if this is true, that in the US civil war, retreating southern troops would blow up possibly useful large buildings by hanging a bag of flour from the ceiling, lighting a fire at ground level, and then shooting a hole in the flour bag as they left. That would be an interesting mythbusters test case, too.
Flour would have to be bone dry.
In the US south, during war, unlikely but possible.
Coffeemate deflagrations discussed upthread require new can in humid conditions.
… waiting for someone knowledgeable to weigh in on the correct definition for “detonation”.
Detonation is where the flame spreads at supersonic speed, deflagration is subsonic
Dust build up on surfaces I’d not be worried about in its own right – if the dust is heavy enough to settle on surfaces it isn’t likely to really stay in the air in sufficient quantities to really do anything, and while generating the dust there will always be some in the air. (Assuming you actually clean the space sometimes – as if that settled dust in 30 years without cleaning and only a really thin skim of the haze you can see has settled…)
Powder is certainly something to be very careful with, and considering how many centuries that has been known with flour mill explosions etc having it happen today is just careless. But at the same time don’t panic about the dust build up on surfaces while say using your circular saw – its going to be really really messy if you don’t have vacuum extration, but the dust is still pretty heavy, so on the whole it will settle quickly enough that it isn’t going to go bang easily, even if you wanted it to. (Which isn’t to say you couldn’t make it happen though).
you actually need to be super careful about build-up becasuse that build up can be unexpectedly disperesed (small nearby xplosion dislodges it into the air, earthquake shakes it loose, a truck hits your building etc) and suddenly that small explosion has a secondary explosion 10x worse than the first.
but don’t worry, they’re defunding the CSB which looks into stuff like this, so it should stop happening all together.
I didn’t mean to suggest you should never clean up…
All I was trying to point out is that to us regular crafty folks with the bulk of our normal use tools the dust produced is largely the type that settles really really rapidly, so a dust build up on the previously clean surfaces while we are working shouldn’t be some great terror – its actually from the POV of explosive dust risk a good thing the surfaces are getting covered, as that means you don’t have as much floaty dust to make the fuel-air mix.
Unless your dusty environment is also an oily one. Then you get that flammable sawdust+oil goo building up. I wouldn’t think that would be explosive but you still wouldn’t want to get it hot! I’ve been told that it is standard safety practice never to have metal machining and woodworking in the same room for this reason.
And that is why my metalworking tools spend time under covers to keep the wood dust crap out as much as possible, and I clean up in my workspace as I do have to do both in the same space. Very different problem to going explosive though – and really just means keep your space clean and tidy up after each major process – which is something you should do anyway as nothing will ruin your paint/finish more than kicking up all that dust you didn’t clean etc..
“Dust build up on surfaces I’d not be worried about in its own right – if the dust is heavy enough to settle on surfaces it isn’t likely to really stay in the air in sufficient quantities to really do anything”
You are wrong about that. The secondary explosion is usually the worse of the two. The initial explosion knocks dust off the rafters and other roof surfaces which immediately ignites.
Dust explosions were just one of a plethora of hazards I had to evaluate as an FM Global (now just “FM”) engineer for over 30 years.
NFPA publishes the equations and software which is a little different from that used by FM.
My point was nothing more than if your work at this moment is covering a surface with fresh dust now it isn’t likely to be an explosive problem – as the air doesn’t have enough in it to do anything. Not that you should never clean up all that potential fuel or you can’t set it off etc! Just that the dust that settles rapidly doesn’t go bang easily as its too large, too heavy, and settles so it doesn’t form that explosive mix. Which is going to be the case for 99.9% of the stuff we regular folks do, as we are not processing the volume or using the tool types that generate high proportions of the fine floaty and thus more explosive dust as a rule.
Possibly apocryphal stories abound in Cambridge University in the UK, which has several ancient open spiral staircases (so no central pole). One student stands at the top and sprinkles flour down the centre, and another stands at the bottom and lights a match…
Stories whispered around MIT told of students perfecting the drop of a bag of flour from the roof the tallest academic building, along with an ignition source, onto the concrete plaza below. No news of blown out windows were reported, but the fireball was spectacular, so I’ve heard.
Flour isn’t super reliable, unless you add a pint of gasoline before the drop.
Then it’s awesome.
You could also dry the flour in an oven first, but less fun.
A kid used to be able to learn these things just watching TV.
https://www.youtube.com/watch?v=8t5iTunRkO4
Do you think Mr Wizard told nickelodeon execs that he wanted to be filmed for others to enjoy, showing different young kids, one-on-one, things that will surprise them, bewilder them a little, and leave them eager to learn more of the topic to pass on to others some day hahaha. Quotes from the video you linked “put your finger in it” “Now rub it” “real slippery isn’t it?”, “you see the tops blowing” “would you like to blow?” — maybe something is wrong with me but I hope you get the idea haha.
Every dust cloud ? so that´s why Sahara is a desert ?
Apothecary diaries?
Burn of gasoline vapors is deflagration, not detonation. Two different things. Google is your friend.
Google is absolutely NOT your friend. They are one of the most detestable entities on the planet.
A gasoline-air mix can do either, depending on the conditions.
I remember Kari Byron describing a dust explosion as the most frightening thing she witnessed doing Mythbusters
https://www.youtube.com/watch?v=yRw4ZRqmxOc
… and mind the static electricity buildup when blowing dust through pipes or hoses: ground every metal part (fittings…) to prevent internal sparks. It works like a Van de Graaff generator.
yea ok have any one of them produced a sun lasting millions of years and backed by evedence?
Makes me wonder, Mars is very dusty, and if they were to actually get people (and mining) on it would you perhaps get issues like this you think? I mean any habitat would have oxygen for instance, and I’m not sure what the composition of the dust is, is it always the same or various mixtures?
I wonder if they thought about that aspect.
(Not that I personally think humans can live on MARS, or even arrive alive and functioning.)
Addendum:
To wit: :The red-orange appearance of the Martian surface is caused by iron(III) oxide (nanophase Fe2O3) and the iron(III) oxide-hydroxide mineral goethite.”
You got your dust your iron and your oxide.