I’m trying to get a sense of how careful I need to be about using Denatured Alcohol containing a large proportion of methanol. (Kleen Strip won’t be specific but says their DA could be as much as 40% methanol).
My understanding is that you can’t chemically filter out methyl alcohol fumes (not that I can find respirator filters in a pandemic anyway), so that just leaves ventilation. What comprises a “well ventilated area”? Is it enough to just have windows open, or do I want to move things along with fans? Or conversely, am I ok as long as I don’t actively huff the stuff? Really hard to get a good sense of the toxicity risk from what I can find online.
(Eye and skin protection is no problem, I’m mostly just wondering how big the inhalation risk is.)
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I have used shellac and therefor DNA for nearly 20 years. An open door to outside has always been more than adequate for hand applied shellac. Once I realized I would come into fairly regular contact with DNA I became more rigorous about wearing gloves.
Just to carefully qualify this . . . I live in a desert basin that has at least a subtle breeze (up to high winds) blowing pretty much all the time. I only keep the shop closed up in what we call winter when temps reach below 50*F. Even then I will do small shellac jobs but, would never spray or do longer sessions.
Safety is best taken seriously. I do not want to give you the impression that caution is not called for. That said, I have never had so much as a dizzy moment or following headache in all my years slinging shellac.
To help you decide http://www.kleanstrip.com/uploads/documents/KS_Denatured_Alcohol_3-19-20.pdf
A very interesting question that has got me doing some significant research.
TL:DR; Methylated spirits or DNA do not pose a significant hazard in the context of their use in woodwork, but should only be used in a well-ventilated area. Use in enclosed spaces may pose a risk of carcinogenesis. Activated charcoal filters are effective at removing methanol.
Using methanol is a potential hazard, but as with all things, the dose makes the poison. It is added to alcohol to get round the duty usually levied on alcohol by making it unsafe to drink. Consuming it is unwise, but even so, the body makes and can handle small amounts of methanol easily. Small quantities of methanol are found in fruit, most alcoholic beverages and even aspartame ( an artificial sweetener) produces some when broken down.
Like most other vapours, methanol can be absorbed into the lungs and in sufficient quantity could be harmful. Methanol is metabolised to formaldehyde (embalming fluid!) and then to formic acid (ant sting chemical), which is then further broken down to folic acid (a vitamin). If you get too much methanol at once, the enzymes that break down the formaldehyde get saturated - you don't have many of them and they are all working flat out - so formaldehyde can build up. Formaldehyde is a known human carcinogen.
This study proves that it can be absorbed through the lungs: https://pubmed.ncbi.nlm.nih.gov/16093526/
It also showed that at 200ppm in air for 2 hours of exposure whilst exercising, no increase in urinary formic acid was detected.
This does not suggest that the exposure was without risk, but it did not seem to stress the ability of the subjects to metabolise the toxic breakdown products.
There have been animal studies which suggest that primates can handle up to 1800ppm, after which there is a risk of toxin build-up, but this has as far as I can tell not been tested in humans.
https://pubmed.ncbi.nlm.nih.gov/15019954/
The problem is that we don't have any evidence of harm or safety in humans. It makes a lot of sense to apply the precautionary principle. 1800ppm is not really that much methanol. In a closed volume of air about the same as an average bedroom, you would need only about half a gram of methanol, or perhaps 5-10g of average meths (the product you link is strangely vague on it's proportions, but seems to have an awful lot of methanol in it)
This means that in a closed room, it would be very easy to expose yourself to enough methanol to create very small amounts of formaldehyde. This is potentially carcinogenic. The longer you are exposed for, the higher the risk becomes.
To be seriously harmed in the short term requires an exposure of 30g or more (about 50-100ml of the product you reference) by oral ingestion. It is unlikely that you would be able to get a high enough vapour density of methanol in any reasonable situation to be able to achieve this by inhalation.
This case report of acute methanol poisoning by inhalation was in the setting of an industrial facility where methanol was being used at high temperatures, resulting in very high concentrations: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4535118/
There are case reports of inhalational poisoning in deliberate solvent abuse inhalation. This is often fatal, especially when combined with toluene.
https://www.revistanefrologia.com/en-methanol-poisoning-caused-by-inhalation-articulo-S2013251418301317
I could not find any cases of accidental methanol inhalation causing harm in the non-industrial environment but there may be a few I missed.
It is wise to apply the precautionary principle and only use volatile compounds in well-ventilated areas. This is just common sense after all. If you do that then the chance of exposure to a harmful level of methanol is negligible.
You can further reduce the risk by using activated charcoal filters, but with good airflow, the risk is small.
Many professionals will use an extractor fan when applying large amounts of volatile finishes. These are cheap and effective.
I know that part of the question here was about stripping. But in the context of shellac, I'd like to plug Zinsser's Seal Coat. It's dewaxed shellac, and methanol free. It uses ethanol, with about 5 percent isopropyl. For me, it beats mixing flakes with methanol, in hardware store DNA. Everclear is not available in my state.
noting there has been some hand sanitizers made with DNA, recalled because of concerns about absorbing methanol through the skin.
Thanks for these great responses.
It certainly makes sense that a common hardware store product shouldn't be too hard to use safely. It's just interesting that "adequate ventilation" is something we all rely on, but can't really define. I've seen the 200 ppm standard, but even if I were able to do the math on evaporation rates and air volume, I would have no idea how he effect of an open window on a still day compares to an open door with desert breezes, or an otherwise closed room with an extractor fan, etc. It's not hard to get neurotic about the minimum standard of care for a product whose toxicity is very real, even if the risk for non-industrial usage is fairly low.
Sounds like any basic effort to keep air moving is going to be adequate. But I'm also going to see if I can find DNA with non-methanol denaturants ;)
I know woodcraft sells a denatured ethanol that uses isopropanol and butanol instead of methanol. The name changed not that long ago. The old name was Becktol. Another approach is to use 190 proof alcohol such as Everclear. If you can't get that in your state, you can order 190 proof ethanol for $100 a gallon. If ordering online, don't order the 200 proof ethanol. Traditionally, one would use benzene (carcinogen) to remove the final parts of water from ethanol . I don't know the process they are using to go from 190 to 200 proof so I would just stick with 190 proof. I've used 190 proof Everclear, denatured ethanol with methanol, ethanol with isopropyl alcohol and butanol. All work just fine.
I use DNA for cleaning up after mixing epoxy. Unless you're gonna bathe in the stuff a simple fan'll keep you safe.
Mikaol
For what it is worth, I an with Mikaol - personally I have no concerns.
On the still air but open window front, that still makes a difference as there will be significant dissipation of fumes through the window.
In such circumstances, pointing a fan out of the window will be all that is required for safety.
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