Aluminum in fire bricks

Is there any concern about the aluminum oxide content in fire bricks and the use of them in the floor of a cob oven? If so, what have others used as the floor as an alternative?

Alumina AL2O3, aka aluminum oxide

Aluminium oxide was taken off the United States Environmental Protection Agency's chemicals lists in 1988. Aluminium oxide is on the EPA's Toxics Release Inventory list if it is a fibrous form. The list governs handling of materials in excess of 25000 pounds.

I posted this because it seems the first thing most permies say when building a cob oven is " go get some fire bricks". As far as I can tell from my research aluminum oxide (which is what fire bricks are made of) is pretty nasty stuff but I am willing to be led to a source that says otherwise.

There are definite and quantifiable health risks associated with exposure to high levels of various aluminum compounds.

But, the exposure levels have to be pretty high to cause a meaningful change in your risk profile.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2782734/


They have studied folks who weld aluminum for a living, and folks who refine/smelt aluminum. Yes, there are some higher risks, but not that much higher.

The other interesting groups are people who eat a lot of aluminum hydroxide in antacids. I don't do those.

There was a big scare about aluminum pans causing alzheimers, but that has largely been disproved. I prefer cast iron myself.

Enteric coated aspirin uses an aluminum compound, but plain aspirin does not.


There was some interesting studies that linked the aluminum in antiperspirant with breast cancer. Again, interesting, but largely discounted these days. Further research is ongoing.

If that's a thing, it may have to do with micro abrasions/cuts from shaving, allowing the aluminum to cross the skin barrier and get into the lymph glands.

Sooooo, maybe we should give up shaving our armpits?


But even in those high exposure situations, like welders, the risk profile is not crazy.


The amount of alumina released from fire brick is pretty minimal.


If you find a good/less toxic substitute, good for you!


Keep in mind, the go to product for decades for these kinds of applications used to be asbestos. THAT is an ugly duck.



Everything is toxic, it just depends on the concentration you are exposed to. That's the first rule of toxicology.


Shit, sand is bad for you. Look up silicosis some time. All depends on the kind of exposure.

I think it makes sense to not take aluminum based antacids, and it's easy to not cook with aluminum pots and pans since they suck generally.

I personally wouldn't worry about the trivial exposure from a hot alumina brick. If you were -making- fire brick, and exposed to the dust, I would take steps to avoid that.




And not that it really matters, but I am a doctor (eye), and I am a machinist with a foundry. I have cast a fair amount of aluminum, so I have a more than casual interest in this subject.

My furnace uses a castable refractory material that is based on alumina compounds. I wore a mask when I mixed it to avoid the dust.

No mental impairment yet, but that's my brain telling me that...

Thanks Troy,

Sure, I get the "everything can kill you argument". If you drink enough water it will kill you right? If we said that about everything we would worry about any pollution, heavy metals, pesticides or herbicides in our bodies.

Fire bricks are 50-75% Aluminum Oxide so that's not really a minute amount. In a wood stove I would have no worries as my concern is not the release through heat but rather the dust embedded in food from the scraping effect on the bottom of the oven. If your scraping off dust from a product that is 50% aluminum oxide your going to get fairly high levels in your body over time.

Yes, I would like to find an alternative, that's why I posted this discussion. I would bet that most that have built cob ovens are not even aware of the composition of fire bricks. Are the same people that would not dare use an aluminum pan ok with using an aluminum brick because it has a cob roof?

Firebrick with an alumina content of 50-75% is industrial grade, suitable for blast furnaces, kilns, foundries and the like. It is extremely durable. For home and commercial use in brick ovens, an alumina content in the 25% range is more suitable, primarily due to cost considerations. Abrasion and wear in home and commercial use is markedly reduced, with cooking floors of brick ovens often lasting for decades. If dust is a concern, placing food on a ceramic or steel plate would mitigate exposure. If this is still not enough to relieve your fears, seeking an alternative means of cooking may be in order. Perhaps a solar oven with no aluminum parts is something to look into.

Amy Woodhouse wrote: wrote:Are the same people that would not dare use an aluminum pan ok with using an aluminum brick because it has a cob roof?

Hmmm...cooking food in a pot is vastly different than the interstitial matrix of a fire brick...industrial or otherwise. I may not use a fire brick that is industrial for want of not supporting the industry behind it, yet the aluminum oxide content is of little concern. This is an "additive" to insure heat resistance and durability, there by making the bricks last longer and in better structural form. I am not eating off of them, nor burning at such temperatures to create an off gassing.

Hope that is helpful and makes sense.

Regards,

j

"Sure, I get the "everything can kill you argument". If you drink enough water it will kill you right? If we said that about everything we would worry about any pollution, heavy metals, pesticides or herbicides in our bodies. "


My point was to remind everyone that "toxic gick" is not a useful conversation if one tries to make two lists. The "A" list being all the bad stuff, and the "B" list being all the good/ok/safe stuff.

Two illustrations will help.

It's tempting to put carrots on the "B" list. Good stuff those organic carrots! And yet, people have literally died from juicing a lot of carrots and overdosing on vitamin A. The dose was too high. At that dose, vitamin A is toxic gick.

Some aluminum compounds, at low enough doses, will have no measurable effect on the person that is exposed to it. Under that dose level, alumina is not "toxic gick".


Just calling something toxic gick doesn't really add very much useful information about product x, y, or z. But once you start looking at real exposure numbers, then we can safely conclude, "Oh, I'm orders of magnitude lower on the dose curve for x, y or z compound, compared to the documented safe level. That's much more useful and helpful information in the real world and can shape strategies to reduce exposure to x, y, or z.


Or, "Wow. It takes trivial/minute exposure to x, y, or z to put me into the higher risk profile for cancer." I think I am going to avoid using that product and find some other strategy.


It's all about the dose.


hth,


troy

An article on Researchgate examines chronic exposure to alumina and bauxite dust.

ABSTRACT To examine the associations between alumina and bauxite dust exposure and cancer incidence and circulatory and respiratory disease mortality among bauxite miners and alumina refinery workers.
This cohort of 5770 males has previously been linked to national mortality and national and state cancer incidence registries (1983-2002). In this paper, Poisson regression was used to undertake internal comparisons within the cohort based on subgroups of cumulative exposure to inhalable bauxite and alumina dust. Exposure was estimated using job histories and historical air monitoring data.
There was no association between ever bauxite exposure and any of the outcomes. There was a borderline significant association between ever alumina exposure and cerebrovascular disease mortality (10 deaths, RR 3.8, 95% CI 1.1 to 13). There was some evidence of an exposure-response relationship between cumulative bauxite exposure and non-malignant respiratory disease mortality (seven deaths, trend p value: 0.01) and between cumulative alumina exposure and cerebrovascular disease mortality (trend p value: 0.04). These associations were based on very few cases and for non-malignant respiratory disease the deaths represented a heterogeneous mixture of causes. There was no evidence of an excess risk for any cancer type with bauxite or alumina exposure.
These preliminary findings, based on very few cases, suggest that cumulative inhalable bauxite exposure may be associated with an excess risk of death from non-malignant respiratory disease and that cumulative inhalable alumina dust exposure may be associated with an excess risk of death from cerebrovascular disease. Neither exposure appears to increase the risk of incident cancers.

In a brick oven, I would not consider dust to be a chronic exposure situation.


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A monograph has been produced by staff of a National Poisons Information Service Centre in the United Kingdom.
It discusses chronic exposure, accumulation in the body, half life times for removal of alumina from the body.

There are some problems with inhaled alumina penetrating the blood brain barrier, being alumina is not water soluble.
Still no statistical risk of cancer from inhalation.

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I think a greater risk would be inhaling the silica dust rather than the alumina dust. This is easily mitigated with an N95 respirator (dust mask). Being this is not chronic exposure environment I would guess you get more silica exposure on a dusty, windy day. However, your concern is the dust on the food. Silica is a problem in the lungs. In the digestive system it passes out of the body.

I appreciate the discussion guys

Troy, when does consumption of aluminum oxide cross over from safe to not safe according the studies you have read?

JC, people traditionally put food directly on the bricks in the oven right? So you are effectively eating off of it and consuming any aluminum particles scraped off the bricks and incorporated into your food....much more than a pot which was the point.
Now, one may say "I am cool with eating minute amounts of aluminum oxide and don't think it will hurt" and I am not saying it will....just trying to hear some opinions as I know there are many that have built them on here and have opinion on the matter.

Ken, the use of the lower aluminum % brick for cob ovens does not seem to be common knowledge in the world of cob oven building. Good point.

JC, people traditionally put food directly on the bricks in the oven right?

I know this is done by many today, so no, we don't cook on them at all, never have.

In most traditional ovens I have used over the decades, when a recipe called for "direct contact" (e.g. flat breads, some meat dishes, some broiling/baking modalities) this was almost always done on a stoneware or soapstone "skid" or "oven plinth." In the very old ovens, or those in rural communities that still use them around the globe, in these cases the bricks one cooks on are hand made stoneware style clay bricks or of a heat resistant stone like soapstone, and do not really require the plinth. I still make and use soapstone oven plinth and can describe, should you want further info, how to fashion an oven plinth of stoneware. They are not that complicated. Most, of stonewear are just a wee bit larger than the item (i.e. flatbread, etc.)

I would also note, that I do not facilitate modern firebrick in many food preparing ovens and only use clay, soapstone, and home made fire brick of stoneware...but that is just me. If a client wants to use a firebrick with aluminum oxide in it...that is fine, as they will not be cooking directly on it anyway. I don't imagine though, after thorough oiling, and seasoning that it would matter much anyway as the fine particulate of oxide in the brick is not going to get into the food, or be dislodged by the wooden peel.

Hope that helped...

Chronic exposure in the studies I linked has workers in aluminum smelting plants. 8 hours a day, 5 days a week, 50 weeks a year for decades.
Firing up a pizza oven now and then does not compare. It's a totally different ball park.
You concerns and fears appear to me as irrational and unjustifiable. The amount of alumina in the food cooked on a well brushed brick oven floor is not quantified. There is no reasonable means of determining your projected level of exposure and determining risk for such minute levels. Uncertainty and risk will always be greater than zero.

We all have differing thresholds of acceptability regarding levels of contamination. For example, some folks have no desire to use manure in compost produced by a beast served feed which includes GMOs. We live in a world fraught with pollution in our air, soil, water, homes and food. There is no escaping it. All one can do is avoid the worst, clean up what we can, and stop adding to it. For the traces which remain, we must accept it as a condition of our environment in order to go on with living and enjoying our lives.

If there is no level of exposure which would ease your apprehension, I would suggest you dismiss the notion of building a brick oven for your own use. Dwelling on uncertainty is no way to enjoy this incredible gift of life.

The last time I read up on the issue, I concluded that the only people who suffered bad outcomes were people who were exposed to aluminum fumes or particulate very often, like every day, and often in "bad" work environments. Or people who ate aluminum based antacids on a daily basis for years.

Example, use of particulate masks was not enforced. Welders were in buildings that didn't have good robust ventilation, that sort of thing. And it had to be going on for years before there were noticeable side effects.



I also have first hand knowledge of a very similar analog. One of my hobbies involves refining scrap lead, and then casting that into relatively pure ingots. Then the ingots get melted again and cast into

bullets. I am also deep into remodeling a 100 year old house that was covered, inside and out, with lead based paint.


So, first order thinking about lead exposure would be TOXIC GICK, RUN AWAY!

A more nuanced and useful approach is to take reasonable precautions and look at actual blood levels and compare that to safe/normal levels.

When I work around lead in its various forms, I use good ventilation when melting and pouring lead, and if it's paint (friable dust generator) I use either an N-95 mask (cheap) or a canister particulate filter mask (35 bucks'ish). Last time I got my blood work done, my lead levels were very low, as in, very safe. Better than average in fact.


So, do we want to have lead thrown around the environment in some wild irresponsible way? No. But do I have to totally shun all lead exposure? No, I'm comfortable with my level of lead exposure, while taking reasonable precautions and actually checking my blood levels.


Can aluminum and alumina mess you up? Yes it can. Is the risk worth taking if you take reasonable precautions? For me, yes. If you control airborn dust, and you don't eat a lot, I think you're good.


In a cob oven, I think if one takes minimal steps to prevent the food coming in direct contact with the bricks, I doubt very much if you will get any measurable exposure to alumina.


Finest regards,


troy

JC, more info on how you construct your cob ovens without aluminum fire brick would be very helpful

Ken, no fear here...just having a discussion which is what these forums are for. Sorry if you think discussing the effects of consuming a heavy metal irrational. The decision is not use fire brick or don't build a cob oven....as JC pointed out there are alternatives for people that choose not to cook on aluminum fire bricks. Not dwelling on uncertainty...just trying to weigh the facts and not do something just because " that's the way we have always done it".

Sorry if you think discussing the effects of consuming a heavy metal irrational...

Hi Amy,

It's not that it is "irrational" Amy...it's that often (I apologize in advance for myself) that we (those I mean with "gray hairs" that have been doing this work for decades...)get a little exacerbated on some discussions when a "topic" is presented from the beginning without good foundational understanding...like the fact that aluminium oxide is not a "heavy metal," nor carries that level of toxicity.

It is fine to ask a question about something that is not well understood...yet often once that "something" is explained by one us "gray hairs,"...many want to debate the answer. That is where the frustration comes into play.

As for my designs, I do plan on documenting the next one I am part of designing and building. I will share that here on Permies...with photos. In the interim there are so many designs to reference I could not begin to describe them all other than to say...you don't need firebrick.

If it is just a simple cobb dome pizza oven, then find a larger (or several large) flat stones that are fire proof. Do this by placing them in a bed of hot coals and then build another large fire on top to "test their temper."

DO NOT collect them in water unless you have a very solid background in geology and ceramic firing!!!

Once these stones are tested and found worthy, they can be used for the floor of the oven.

I have gone as far as taking several smaller "flattish" heat resistant thick stones (when I don't have steatite) and scribe fit/carve them to each others profile for a perfect no grout fit...then...bush and/or grind the tops to be perfectly flat level. Upon this I build the oven....

Regards,

j

Ah, my foundational understanding. From Wikipedia: "Beryllium and aluminium, although light metals, are sometimes counted as heavy metals in view of their toxicity" This was meant to be a discussion with dialog and there was no intent to offend any gray hairs.

Absolutely no offense take on my part Amy...just 'internet' based frustration perhaps...not to worry.

If I answered well your queries then I am pleased......if you have more you want, that I may address, please by all means...pull my gray hairs...

I am glad to answer....I would note that most firebricks, after proper "seasoning" are probably just fine to use and are safe. If concerned...use stone.

Warm Regards,

j

P.S. Wiki is a neat place to go...sometimes...but I find as much "incorrect info" as I find factual....be careful in that realm. Also, I did not mean to offend with my comment about "foundational understanding." We all start some place...that is how the foundation is built. Good to have you asking questions...yet do accept the answer given... unless you have good reason to differ from it...Debate can be healthy and we can all learn from new perspectives.

Amy Woodhouse wrote:Ah, my foundational understanding. From Wikipedia: "Beryllium and aluminium, although light metals, are sometimes counted as heavy metals in view of their toxicity"

In their solid form, neither is particularly toxic. Most concern comes from dust from cutting. Aluminum oxide(Al2 O3, which is the kind we are talking about) is the 4th most common material in the earths crust after silicon dioxide, magnesium dioxide, and ferrous oxide.

JC, NIH.gov also has medical papers on its website which label Aluminum under heavy metals if you don't like Wiki. And no offense taken, I find it humorous.

Right Bill, What we are talking about is the aluminum dust that is inevitably scraped off the bricks during use and then ingested via food placed on said brick. This is not relevant for stoves or people that don't cook directly on their fire brick (which most people do).

Ok, here is some math..JC use you gray hair and check the numbers.

A typical fire brick is 4.5" x 2.5" x 9" which is 101.25 cubic inches.
If you use 26 bricks for a 36" x 36" cob oven you have 26 x 101.25 = 2,632.5 cubic inches of fire brick
Lets assume each brick is 25% aluminum by volume (which is what a manufacturer told me is the lowest % aluminum they make) so you have 2,632.5 x .25 = 658.125 cubic inches of aluminum
There are 14.4375 cubic inches in a cup so you have 658.125/ 14.4375 = 45.5 cups of aluminum
A cup of aluminum oxide weighs 934, 523.54 mg so you have 42,520,796.5 milligrams of Aluminum Oxide in your cob oven.
The CDC says as long as you don't ingest over 1 mg of aluminum per day (or 1/40,000,000th of your bricks) you should not have any adverse health affects.

So there you go, regardless of hair color, those are the facts so everyone can make an informed decision. Let me know if I made a math error anywhere and I will update the post to correct it.

Not getting into the toxicity or lack thereof, I have a few questions and comments about your math and chemistry. First, did the manufacturer say the 25% is by volume or by weight, and is that aluminum or aluminum oxide? Those factors would significantly affect the amount of aluminum in the bricks. I think the relevant factor is how big a volume weighs a milligram, thus how much powder would need to be scraped off with each pizza to be hazardous. If a milligram of firebrick powder (1/4 aluminum or 1/4 aluminum oxide, whichever it is) is a decent pinch, I think we can agree that nowhere near that much comes off with each pizza, let alone gets into the food or air that a person consumes. Hard firebrick are quite abrasion resistant, soft firebrick are not (and thus are not suitable in any way for an oven floor). I don't have equipment to measure a milligram of firebrick powder, but I could weigh out 0.1 gram and see how big a pile/pinch it is.

Amy Woodhouse wrote:
Right Bill, What we are talking about is the aluminum dust that is inevitably scraped off the bricks during use and then ingested via food placed on said brick. This is not relevant for stoves or people that don't cook directly on their fire brick (which most people do).

The dust I am talking about is the dust relating to industrial cutting of the substances. Incidental dust is not what they are talking about. There is no reasonable level of concern regarding the USE of fire bricks. All of the "toxicity" concerns are concentrated on manufacture or cutting of fire bricks on a large scale. Breathing in lots of mineral dust is simply intrinsically unhealthy, regardless of the substance. Fibrous forms of minerals are dangerous for the same reason.

Glenn Herbert wrote:Not getting into the toxicity or lack thereof, I have a few questions and comments about your math and chemistry. First, did the manufacturer say the 25% is by volume or by weight, and is that aluminum or aluminum oxide? Those factors would significantly affect the amount of aluminum in the bricks. I think the relevant factor is how big a volume weighs a milligram, thus how much powder would need to be scraped off with each pizza to be hazardous. If a milligram of firebrick powder (1/4 aluminum or 1/4 aluminum oxide, whichever it is) is a decent pinch, I think we can agree that nowhere near that much comes off with each pizza, let alone gets into the food or air that a person consumes. Hard firebrick are quite abrasion resistant, soft firebrick are not (and thus are not suitable in any way for an oven floor). I don't have equipment to measure a milligram of firebrick powder, but I could weigh out 0.1 gram and see how big a pile/pinch it is.

I specifically asked that when talking to the manufacturer and they said it is not by weight but by volume. I also found out what a cup of aluminum oxide weighs in mg (I state this in my calculation) for my conversion to weight and thus milligrams. I also called the CDC and they said 1 mg a day is the amount you can consume in all of your daily activities and be fairly sure not to get sick. And then I determined how many milligrams of aluminum oxide are in small cob oven. To give you an example that everyone can visualize, 1 mg of water is 1/50th of a drop of water from your average dropper...hardly a decent pinch. The result is the result...everyone can make their own determination as to the risk.

Hello Amy,

Your arithmetic looks o.k. to me at first glance...I am not sure how extrapolative it may be to levels of "potential toxicity" as it may relate to LD amounts as measure by MSDS. I do agree with mitigating exposure to cooking directly on pure aluminum, as such we have no aluminum pans, nor cook on aluminum foil in our house. Yet all I know and understand about Aluminum Oxides that are in and around me all the time leaves me much less concerned. It is in floor finishes that many folks use and walk on; food prep locations, sandpaper, etc...and the list continues. I suspect...in the larger scheme of aluminum exposure...this discussion is more academic than any real health concern. As was shared with me by others, the view I have discussed this with for this post...using one sanding disc, or general environmental exposure in the world today with aluminum oxides use in so many products will expose the average person to way more of this molecule than if you ate every meal for the rest of your life prepared on a "firebrick."

I have been using (as have thousands of others) aluminum oxide sanding and polishing discs for over 30 years. My exposure rate to an actual known HD form of AO is 1000 times higher (rough average) than what anyone using fire bricks would be exposed to...as is most professional woodworkers. In our field it has been determine that the actual "wood dust" is much more of a concern to health than anything else generated by AO exposure.

So again...individual choices...yet I believe, and from what I have ascertained from others during this discussion...AO in firebrick is of little to no concern unless you are carving and shaping it on a professional and constant basis...For the sake of "peace of mind," for those needing to use firebrick for a Permies project...I think there is most more pressing (and health related) things to worry about and consider than whether to employ firebricks or not in a design...I don't typically use them more out of liking to make things from scratch and being a stone carver, and would add, after the research I have just done for this post thread...I am less concerned now about AO than I was even in the past...

Regards,

j

Aluminum content of soil averages around seven percent...it's the most abundant element in the earth's crust. We grow our food in it and breathe the dust all the time. We probably shouldn't be ingesting aluminum ingots, but there doesn't appear to be any feasible way of avoiding constant incidental contact.

I read a book on Chinese medicine some time ago and it said that aluminum in metallic form has very strong yin quality, strong enough to rob very yang ginseng of any beneficial qualities. I've tried to avoid aluminum food items ever since.
Aluminum in a form of an oxide could be an entirely different game thou. I don't know. But considering the abundance of it, i imagine, whatever it is it's well balanced by the rest of the system.

I don't care what the ongoing studies say, there is clearly a link between aluminum and neurological disorder in humans. It has long been well known that workers who breath aluminum dust or breath aluminum fumes perform lower than average on some tests that measure functions of the nervous system.

Some areas have higher aluminum content in the soil than others.

Aluminum is a non essential nutrient.

Victor Johanson wrote:Aluminum content of soil averages around seven percent...it's the most abundant element in the earth's crust. We grow our food in it and breathe the dust all the time. We probably shouldn't be ingesting aluminum ingots, but there doesn't appear to be any feasible way of avoiding constant incidental contact.

There are ways to avoid it, like you said on average al. content in soil is 7%, some soils much higher some lower. If you limit your exposure to foods grown in these high Al. content soils you could reduce your intake.

The soil ph has a lot to do with it as well as the ph of the fruit/veggy. Pineapple for example has much higher aluminum concentrations than other fruits due to the soil its grown in (acidic low ph, high al. tropical soil) and the acidity of the fruit itself.

Amy what about something like this? I have been looking for a long time to find the oven I want and this one is really neat. Combines the best of both worlds I think!


http://slice.seriouseats.com/archives/2011/10/slice-over-a-barrel.html

Hey folks. I lurk on here quite a bit and thought I might be able to help in this regard. I am a working potter and industry glaze chemist and can shed some light here. First, as noted earlier toxicity is a matter of exposure rates... However there is also the format of an exposure to consider. For instance silica, one of the dangers in my line of work is mostly harmless ingested but harmful if inhaled. Also we must look at the nature of the compound you're exposed to, and example here is Barium oxide and carbonates that are used as rat poisons and Barium Sulfate which is used to provide contrast in an MRI this is possible because unlike the oxide and/or carbonate formats are soluble while the sulfate is not.

Now to the point of alumina (which is what we call Al2O3 in the ceramic industry)... The difference between glass and ceramic is alumina. So litterally every single piece of ceramic you have ever encountered has exposed you to alumina. Everything you drink out of or eat off of, unless you use paper or plastic (in which case we can't be friends). The oxidized form of alumina is highly stable, insoluble, and largely non toxic. Compare the melting points here with metallic aluminum melting just over 1200 F and alumina melting at over 3700 F. As a final note while you never need a brick with that alumina rating for an oven, any firebrick would be pretty damn stable at even high pizza oven temps of 1000 or so degrees... cook the shit out of them pizzas and rest easy.

Hey James......welcome!!!

Please don't lurk anymore...that was a great post and wonderful information to share...Thanks so much!!!

Here is another post worth reading and would love your view points on...Please do share them!!

Homestead scale pottery manufacture...

Big welcome again, and Regards,

j