Sciencemadness Discussion Board - Fire & Explosion risk vs. scale

Fire & Explosion risk vs. scale

Sulaiman - 11-1-2018 at 04:18

I started with 10/19 glassware with 50ml being my largest flask size,
so I was handling typically 30ml batches of chemicals,
with only minor safety concerns, other than toxicity.

I very quickly moved up to 24/29, and my largest flask size became 500ml,
so I now have a few dry powder extinguishers and a garden hose handy,
I've been operating under the assumption that I can handle a few hundred millilitres of boiling flaming solvent,
as I always do this kind of stuff outside.
..........................................................
Secret Santa made my wish come true ...
so I will soon be using a 2000ml flask, with possibly 1.5 litres of boiling solvent etc.
and
I do not think that I am ready to handle a worst-case scenario

Although boring, tedious and probably more expensive than the glassware,
I feel that I need to take this hazard very seriously.

The main scenarios that I envision are mostly common solvents distilled at atmospheric pressure using an oil bath (using a vessel of greater capacity than oil + solvent) and probably kerosene distillation at reduced pressure.

So, could anyone here that has experienced a solvent fire in the litre range care to comment ?

[Edited on 11-1-2018 by Sulaiman]

j_sum1 - 11-1-2018 at 05:15

Get a decent sized fire blanket.
I don't have any more experience than you do in this matter but I do know that a blanket followed by extinguisher is a lot more effective than extinguisher alone.

AJKOER - 11-1-2018 at 05:43

My personal viewing of a childhood friend into chemistry that created and detonated some 5 ml of NCl3 (classified apparently correctly as a HE) demonstrated to me that micro sizes of any highly energetic material is the only rational behavior with safety measures in place!

There is a rough rule that the relative power of an energetic compound increases according to a third power rule. So, doubling the weight could produce an event that is 8th times as strong. Triple the weight --> 27 times..., 10 fold --> 1,000 times,..., 100 fold --> 1,000,000 times.

So, my advice, focus more on what may accidentally be formed (as NCl3 can be) and avoid false confident on flash size.

Metacelsus - 11-1-2018 at 05:52

Quote: Originally posted by AJKOER

There is a rough rule that the relative power of an energetic compound increases according to a third power rule. So, doubling the weight could produce an event that is 8th times as strong. Triple the weight --> 27 times..., 10 fold --> 1,000 times,..., 100 fold --> 1,000,000 times.

No, this is blatantly wrong. If anything, the destructive power by overpressure increases as the cube root (1/3 power).

Edit: for an explanation, see this book.

[Edited on 1-11-2018 by Metacelsus]

happyfooddance - 11-1-2018 at 07:27

Quote: Originally posted by Sulaiman

Secret Santa made my wish come true ...
so I will soon be using a 2000ml flask, with possibly 1.5 litres of boiling solvent etc.

[Edited on 11-1-2018 by Sulaiman]

You must have heard this but I'll say it again, you never should fill a boiling flask more than half full. Boiling flasks are most efficient when they are half full (filling it up more just gives the liquid less surface area to evaporate, so it distills more slowly, and the liquid and evolving vapor have no room to safely splosh around). That extra half liter that you want to add for no good reason will be the start of your fire.

AJKOER - 11-1-2018 at 07:38

Quote: Originally posted by Metacelsus

Quote: Originally posted by AJKOER

No, this is blatantly wrong. If anything, the destructive power by overpressure increases as the cube root (1/3 power).

Edit: for an explanation, see this book.

[Edited on 1-11-2018 by Metacelsus]

Some research suggests that Metacelsus comment is correct (see Figure 4-5 at https://www.fema.gov/media-library-data/20130726-1455-20490-... ).

A corrected comment would have been in relating changes in an explosive charge size, as measured by diameter of a spherical projectile, to explosive effect (see https://books.google.com/books?id=rfVOAAAAIAAJ&pg=PA791&... ). To quote:

"The weight of explosive carried increases as the cube of the diameter, but experiments have shown that the destructive effects caused by the explosion of a high explosive shell charge increases in greater ratio than the cube. It will therefore be understood that an exceptional advantage is to be attained from the fact alone that the weight of the shell charge is increased. "

Note, it is expected that the relative weight change in this instance relates to the change in volume of a sphere given by V=4/3*Pi*r^3 or, in terms of diameter, V=1/6*Pi*d^3 as r=d/2).

[Edited on 11-1-2018 by AJKOER]

happyfooddance - 11-1-2018 at 08:51

There is a huge difference in destructive power between a liter of liquid on fire in a flask or beaker, and that same flaming vessel breaking or spilling. I have worked in kitchens my whole life, so I have seen and stopped more than my fair share of fires. I have seen fryers with 30 liters of oil at almost 200° C spew flame and smoke into the air. For the most part removing oxygen is the best thing you can do, this of course does not work when oxidizers are part of the fire. The aforementioned oil fire was stopped by laying a large sheet tray over the fryer.

One thing you learn in a kitchen is to adjust some of your reflexes. For example, when something falls over or off the countertop, one's instinct might be to catch it before it falls. What if that thing is a knife, or a hot saute pan? So you let those things fall, but it takes some vigilance and maybe a little reconditioning.

Which brings me to my scary lab fire story. Long story short, I was holding a large mason jar half filled with hexane (top layer), when it was ignited by a covered flame that was about four feet away. There was a whoosh, flames shot in my face, I jumped a little but thankfully didn't spill hardly anything, and I set the flaming jar down and covered it with a lid. I had no burns, just lost some hair from the top of my head, my arms, and strangely, my belly (my shirt must have pulled up as I jumped). The scary thing is that initially my reaction was to drop the jar and jump back. I am grateful for the experiences that I have had and they make me a better chemist, but it is best to prevent accidents rather than mitigate them.

A good thing to do would be to go to your outdoor distilling spot, take a liter of water and dump it on the ground, and see where the water flows, how far, which direction... To simulate a worse case scenario. If it flows right into the side of a building, you might want to pick a spot farther away for flammable liquids.

Also, in general, all the chemicals you work with have properties that you should be familiar with and build a frame of reference for. Whenever you are working with a chemical and especially when you are heating it, you should be at least roughly aware of: vapor pressure at room temp., b.p., flash point, auto-ignition temp (that's a big one often overlooked), there are others but you get my drift.

Sulaiman - 11-1-2018 at 09:03

j_sum1
good idea, I'll order a fire blanket

AJKOER
I intend using this scale just for solvent recovery etc.
my actual experimenting is done at smaller scale
but thanks for the reminder

Metacelcus
Nice to know that I'll only be doubling my explosion risk

but it is the fire risk that I fear most.

happyfooddance
I understand what you are saying but
the surface area when 3/4 full is the same as when 3/4 empty
so if there is not too much foaming I'll probably ignore your correct advice.
I honestly do not know how I would react under all circumstances, I rarely panic, but I'm getting older and slower

[Edited on 11-1-2018 by Sulaiman]

happyfooddance - 11-1-2018 at 09:11

Quote: Originally posted by Sulaiman

happyfooddance
I understand what you are saying but
the surface area when 3/4 full is the same as when 3/4 empty
so if there is not too much foaming I'll probably ignore your correct advice.

This is true, but a 3/4 full flask takes 3 times the energy to heat as a 3/4 empty one. Foaming is not the issue, splashing liquid is.

I could explain so many more reasons, but you will just have to see for yourself.

Edit: The bottom line is, and others with experience can back me up, but you could distill 1000ml twice, in about the same time that you can distill 1500ml once, in a 2l rbf. So what would be the point

[Edited on 1-11-2018 by happyfooddance]

Sulaiman - 11-1-2018 at 09:59

In my case the point is that I'm trying my hand at fine fractionation
and setup times are almost constant, regardless of batch size,
so larger batches are more time efficient
BUT I will keep your advice in mind.

wg48 - 11-1-2018 at 10:02

Quote: Originally posted by Sulaiman

I feel that I need to take this hazard very seriously.

The main scenarios that I envision are mostly common solvents distilled at atmospheric pressure using an oil bath (using a vessel of greater capacity than oil + solvent) and probably kerosene distillation at reduced pressure.

So, could anyone here that has experienced a solvent fire in the litre range care to comment ?

[Edited on 11-1-2018 by Sulaiman]

My only experience was with a chip pan fire started by my wife. She had been waiting for the oil to boil!!! WTF, Three foot high flames, managed to turn of the gas and move the pan into a stainless steel sink where I placed a metal lid on the pan, then covered it with a damp tea towel which eventually smothered the flames.

You have the first problem of containment covered if the contentment item is metal preferable stainless steel well mounted. Next nothing combustible within flame range and a way of turning of the heat source remotely and a fire blanket to smother the flames which will be difficult with glassware sticking out of the top of the area. Perhaps a slotted or two-part metal lid would be useful.

I would advise against an oil bath unless your outside and even then if you have neighbours do you want to freak them out.

happyfooddance - 11-1-2018 at 10:38

Quote: Originally posted by Sulaiman

In my case the point is that I'm trying my hand at fine fractionation
and setup times are almost constant, regardless of batch size,
so larger batches are more time efficient
BUT I will keep your advice in mind.

I feel like I am beating a dead horse, but...

I see what you mean, and trust me, everyone thinks it is a good idea to put more in and save on set-up time. We have all done it, but it is clear to me that you don't have the experience in doing this, and I regret to inform you that even with your best intentions this won't work out well for you.

When I am using a tall column I too will fill the flask up a little extra. In a 2l flask, lets say 1200 ml, MAX. Probably more like 1180. Those 20ml make a difference. 3/4 full is WAY too much, especially if you are trying to get "fine fractionation". That headspace is your friend, and akward splashing effectively pushes/pulls vapor through your column, rather than letting it fill the column by gravity. Very little fractionation occurs.

More importantly, unless your heating element is in the flask, you will be heating the outside of the flask. A mantle will struggle even when set too high, an oil bath will struggle, and you will need to lower the bath or raise the set-up as the distillation proceeds. The point is, that you will need to apply much more intense heat, but your liquid can't evaporate at a rate to match, thus it becomes superheated, and then all at once bumps, through your column, condenser, on the floor. Granted you will have a half a liter in your recieving flask, but it won't have been distilled.

If your issue is batch size, buy a 3l flask. Using the wrong size flask is not a solution, and in the case of "boiling hot solvent", it certainly isn't safe.

SWIM - 11-1-2018 at 10:42

The proposition that explosive damage increases with the cube root of the power seems to be consistent with some very detailed damage calculations about nuclear blasts that were done during the cold war, and confirmed with actual above ground testing (spooky test footage; my how those pigs do squeal when the thermal flux catches up with them!).

I've always settled for fire extinguishers, but A fire blanket sounds like a fine Idea.

I heat with mantles a lot for larger, more risk averse flammable reactions and solvent recovery because with the mantle suspended above the counter there's room for a pan of sand under the boiling flask. I even have a magnetic stirrer that can be mounted on the ringstand to leave the bench clear for the pan. (cobbled together from a small multi-speed kichen mixer and a few odds and ends)

I've never actually had to resort to the Pan-and-cookie-sheet method of fire suppression, but I think it would be workable, and even if I don't manage to snuff the fire quickly with the cookie sheet, having it in the pan sounds a lot better than a flaming puddle in your fume hood or, worse yet, on the floor.

Sulaiman - 11-1-2018 at 10:46

You are correct about my lack of experience
and since you have taken the effort to clearly warn me
I will definitely follow your advice.
Thanks

happyfooddance - 11-1-2018 at 10:52

Quote: Originally posted by Sulaiman

You are correct about my lack of experience
and since you have taken the effort to clearly warn me
I will definitely follow your advice.
Thanks

You are very welcome. By all means, try it out, but maybe on a bit smaller scale. About 500ml the superheating thing can become a real issue. It almost never happens on a scale smaller than that, unless you forget boiling chips.

Also, never forget boiling chips, and if you do, DON'T add them to hot liquid.

Sulaiman - 11-1-2018 at 11:36

For my 500ml flasks I use a diy mantle
(so far, 380W max. input, 175W effective heating, with still evolving magnetic stirring)
I think that I can get my still to run faster, maybe double, with more heat, so
I need a new heater for my new 2l flask(s),
and as I already have a hotplate and suitable pot for oil that seems the way to go.
I have no experience with boiling chips but I will be using overhead stirring, with a sparky d.c. motor

MrHomeScientist - 11-1-2018 at 13:37

With boiling chips, the advice to never add them to hot liquid is because it can cause sudden, violent boiling that can splash hot liquid everywhere. To my shame, I have added boiling chips to hot liquid a few times

but thankfully have not had that accident yet. Interestingly, my experience goes the opposite direction - they don't work at all! So either way, always add them before applying heat.

weilawei - 11-1-2018 at 14:12

Boiling chips are porous and become saturated over time, leading to eventual superheating. I have boiling chips, but they're inconvenient to use, which gives me a preference for strong stirring with a teflon stirbar. I've never had an issue with stirbars, and you can use an overhead stirrer for viscous mixtures. They're infinitely easier to separate and clean. A good magnetic stirrer hotplate (like the Corning PC models) is worth its weight in gold. The other thing to consider, especially for vacuum distillations or distillations prone to bumping is the use of a gas capillary to introduce air or inert gas bubbles.

[Edited on 11-1-2018 by weilawei]

happyfooddance - 11-1-2018 at 14:12

Quote: Originally posted by MrHomeScientist

With boiling chips, the advice to never add them to hot liquid is because it can cause sudden, violent boiling that can splash hot liquid everywhere. To my shame, I have added boiling chips to hot liquid a few times

but thankfully have not had that accident yet. Interestingly, my experience goes the opposite direction - they don't work at all! So either way, always add them before applying heat.

To my shame as well, I have on a few occasions added chips to a hot liquid, and have been splashed with a fair amount of boiling liquid. On several occasions. You can try adding them super slowly, but sometimes all it takes is one chip to make the pot erupt.

I have never heard of boiling chips not working, I suspect you were using glass? There is an oft-repeated fallacy that broken glass will work as boiling chips. It will not, even if it is etched, or broken ground glass joints. Glass is simply not porous enough.

Also, boiling chips stored in the freezer are noticably more effective, I am guessing because they absorb more gases at colder temperature.

Broken coffee mugs, crushed, boiled in a little nitric acid, then water, then dried in the oven, stored in the freezer. Carbon chips work great for alcohols.

zed - 11-1-2018 at 15:46

Experience is good, but it doesn't totally vaccinate against making a dumb mistake.

So many variables! So easy to overlook, or make a small miscalculation.

Fireblanket? Harbor Freight is offering an 8ftx8ft Glass blanket for about 35$ US.
With a discount, and they usually offer a discount, it comes to about 30$ US.

The 6x8 is a little heavier and more expensive, and it is sealed or impregnated with something. Still, with the common discount, 20-25%, it is inexpensive enough.

https://www.harborfreight.com/6-ft-x-8-ft-professional-fiber...

Whoops! Has an acrylic coating. I don't like the looks of that. Better overall quality, vulnerable coating.

[Edited on 12-1-2018 by zed]

[Edited on 12-1-2018 by zed]

[Edited on 12-1-2018 by zed]

NEMO-Chemistry - 12-1-2018 at 17:27

I have had alot of fires, hence one the reasons i am going down in scale!

Worst fire apart from the chimney, set the curtains on fire and the wooden shiplap ceiling had to be replaced. For the most part it was actually kind of under control! I had an extinguisher, i had a fire blanket. But I did make mistakes.

So my current routine based on maybe 8-9 fires mainly small size but scary.

1) Put the fire extinguisher by the door and on the wall, on the wall because its easier to grab and you dont cover it up with shit or put stuff in front of it, you also always know where to find it.

By the door because by the time you get to it, your hopefully moving away from the fire, look back. From one experience I decided fuck it, and didnt try and put it out. I was real lucky it burnt fast and looked bad, but was over in 40 seconds top!

2) ALWAYS have a clear ROUTE directly to the door! NEVER EVER start work if you got to climb over stuff etc, some fires can trip the electrics, especially hotplate ones that trip all the electrics

. You want a clear way out.

3) Fire blanket on the wall near to work space, if a fire starts then try the blanket straight away. Then go for the extinguisher and see rule 1.

4) This is what has caused me so many fires, ALWAYS put the fucking solvents away when not actually in your hand being used!

Put them away from your work area and heat source!! If you use Ether or Petrol then you got fumes on the floor, trust me you do! When using those solvents vent the area before starting a heat source, use the following routine...

Solvent out, lid off, pour solvent, lid on and put away. THEN start heat sources etc.

5) Dont use an oil bath for stupid stuff like boiling conc sulphuric acid, or oil baths with flasks with water in etc. infact unless its a steam bath i dont like water baths at all. use silicon oil or better yet a mantle.

6) Dont be a hero, walk away if you get to the fire extinguisher look back and think, shit not sure about this. Just walk away.

7) Second reason I havnt had a fire for a little while (chimney dosnt count), always assume your experiment will go up in flames! I started doing this and it changed how I work and what I do. i have metal covers and pans to hand that can smother, i dont have bottles of solvent near the hot plate when its on. I dont leave caps off or chemicals out.

8)Make sure your insurance will cover it, in our case the fire with the curtains etc the insurance company refused to pay out!! £900 it cost to put right. Dont do dangerous shit or unattended stuff in the house ever.

If you work in the house then bladder empty before experiment and again after. You dont need or want to get/do anything else while your experiment is active inside the house.

Sheds are different, if it burns then tough. At least you still got a bed for the night (wife dependent obviously).

Bert - 12-1-2018 at 19:02

The door to a lab/danger area opens OUTWARD and will open by just being pushed, no time wasted finding and using complex mechanisms like door knobs while your hair is on fire...

Reboot - 12-1-2018 at 19:18

PLAN for failure.

Assume the glassware will break/get knocked over. Got a spill kit? Can your bench/hood contain a spill? If your distillation flask cracks under thermal stress, could the contents ignite from, say, your hotplate/mantle?

Assume everything you handle will get dropped/spilled. Is it OK for chemical X to get spilled on the floor? What's your plan if that bottle of methyl iodide goes everywhere?

Assume your fume hood/ventilation system will fail. Is the reaction something you can shut down, or safely deal with anyway? If not, what's your backup plan? Got a respirator with the right cartridge type ready to go? A nearby window you can open?

If you're dealing with highly toxic gasses (like hydrogen sulfide), do you have a monitoring system in place?

Assume a fire will start. Do you have at least a good extinguisher handy?

If it might be explosive, assume it's going to blow up. Do you have the right personal protective equipment/blast shields/etc. to contain it WHEN it happens? (And related, decide just how much you really need to make. Danger is always partly a function of scale in chemistry.)

NEMO-Chemistry - 12-1-2018 at 19:24

Clay based kitty litter cheap as and nothing beats it for spills! I left 40KG of dead batteries I had collected in back porch. I forgot about them and many months later they had leaked out the bags.

Man the mess was unreal, 10KG of clay kitty litter took the lot up off the floor and cost £4 all together

NEMO-Chemistry - 12-1-2018 at 19:25

Quote: Originally posted by Bert

The door to a lab/danger area opens OUTWARD and will open by just being pushed, no time wasted finding and using complex mechanisms like door knobs while your hair is on fire...

Shit Bert last fire i had i didnt bother opening the door on the way out lol

LearnedAmateur - 13-1-2018 at 05:00

I assume this is common knowledge but I’ll add it anyway since it hasn’t been mentioned - never use water to extinguish a solvent fire. Dumping water onto an immiscible solvent will just cause it to float and keep burning, riding the water and going where it flows, and spraying with a hose will likely end in the fire becoming even more widespread. Not so much a problem with ethanol and such (mist setting), but kerosene, DCM, toluene etc. is the real issue. An even bigger danger is if the solvent has a higher boiling point than water, as is a common cause of housefires - for example if you have an oil fire, attempting to extinguish with water will lead to it sinking and instantaneously boil, launching hot, firey droplets everywhere and making the issue impossible to contain.

I only work with <100mL at a time so I’ve never had a fire myself, even when boiling 10-20 mL of solvents in a boiling tube using a blowtorch flame which I can do quite comfortably.

As for boiling chips, I use rough marble chips about 5-10mm in size that have been treated with dilute H2SO4 to form an inert and insoluble coating of CaSO4. These work pretty great for most applications and I’ve never had them interfere with a reaction. From personal experience, I too have attempted to use glass shards as chips but I’ve found that they cause the boiling to be more violent and tend to jump around a lot - mineral based chips produce more consistent nucleation with smaller bubbles leading to a gentle simmer/rolling boil.

[Edited on 13-1-2018 by LearnedAmateur]

NEMO-Chemistry - 13-1-2018 at 08:07

Quote: Originally posted by LearnedAmateur

I assume this is common knowledge but I’ll add it anyway since it hasn’t been mentioned - never use water to extinguish a solvent fire. Dumping water onto an immiscible solvent will just cause it to float and keep burning, riding the water and going where it flows, and spraying with a hose will likely end in the fire becoming even more widespread. Not so much a problem with ethanol and such (mist setting), but kerosene, DCM, toluene etc. is the real issue. An even bigger danger is if the solvent has a higher boiling point than water, as is a common cause of housefires - for example if you have an oil fire, attempting to extinguish with water will lead to it sinking and instantaneously boil, launching hot, firey droplets everywhere and making the issue impossible to contain.

I only work with <100mL at a time so I’ve never had a fire myself, even when boiling 10-20 mL of solvents in a boiling tube using a blowtorch flame which I can do quite comfortably.

As for boiling chips, I use rough marble chips about 5-10mm in size that have been treated with dilute H2SO4 to form an inert and insoluble coating of CaSO4. These work pretty great for most applications and I’ve never had them interfere with a reaction. From personal experience, I too have attempted to use glass shards as chips but I’ve found that they cause the boiling to be more violent and tend to jump around a lot - mineral based chips produce more consistent nucleation with smaller bubbles leading to a gentle simmer/rolling boil.

[Edited on 13-1-2018 by LearnedAmateur]

Boiling chips i use bits of broken coffee mugs, i have a regular and ample supply of these. they are normally heavily glazed and pretty inert IMHE.

LearnedAmateur - 13-1-2018 at 09:07

I’ve heard that anything ceramic/porcelain based is fine for less stringent applications, plus it has some natural porosity to them. I have quite a collection of marble chips so I prefer those, plus they’re reusable with a small wash between uses - the only thing that turns me off of broken mugs is that the glazing does decrease surface area which is where the marble excels. Albeit, I’ve never used them, and since they’re recommended I don’t have anything to say against it, especially since mugs can be found in just about any home whereas marble may not.

NEMO-Chemistry - 14-1-2018 at 03:46

Quote: Originally posted by LearnedAmateur

I’ve heard that anything ceramic/porcelain based is fine for less stringent applications, plus it has some natural porosity to them. I have quite a collection of marble chips so I prefer those, plus they’re reusable with a small wash between uses - the only thing that turns me off of broken mugs is that the glazing does decrease surface area which is where the marble excels. Albeit, I’ve never used them, and since they’re recommended I don’t have anything to say against it, especially since mugs can be found in just about any home whereas marble may not.

My lab has a fresh broken mug most days

, actually its the handles I break, if you want more surface area then an angle grinder does a fine job taking the glaze off.

tommy claisen - 25-2-2018 at 07:03

if it's an option, i would recommend distilling solvents using a slight vacuum (650mm Hg, CO2 trap) so that a bubbler w/ inert gas can be used. no chips needed.

Sulaiman - 25-2-2018 at 10:06

Dry ice is tooexpensive for me so almost all distillations are at atmospheric pressure.
I do intend to use reduced pressure for kerosene distillation.
The thought of a superheated solvent fire still terrifies me - way beyond just respect,
but I guess that's a good thing.

I've modified my diy 500ml heating mantle to incorporate a 2l pyrex bowl around/under the mantle/insulation,
above the magnets, to catch liquids - to give me get away time at least

P.S. Even though I've never used boiling chips I believe that I do understand why and how they work.
superheated liquids cannot easily vapourize other than at a liquid/gas boundary, which is normally at the surface, or an existing submerged bubble, in a porous material, capillary tube, or simply added via an air leak.
Once a bubble is available to evaporate into, the bubble grows rapidly.
Without a nucleation site it is very difficult to start a new bubble due to surface tension.

[Edited on 25-2-2018 by Sulaiman]

BaFuxa - 26-2-2018 at 06:14

In my experience, boiling chips are not perfect to prevent bumping. I have had bumping occur even with glass chunks and sand. What works very well is a rotating stir bar.

If you plan vacuum distillation then you should set up a cold trap otherwise your pump will get ruined.

But you can do it without vacuum, I have distilled some gasoline in a 500 ml rbf without vacuum two times and nothing spectacular happened. It just stinks. Just monitor the temperature to stay clear of the autoignition points of the most volatile compounds and you are fine. I never pushed it above 68°C. Ventilate well or do that in a fumehood. The smell is horrendous and sticks everywhere.