Thread: Cyanide in polyurethane finishes

Thanks ... excellent job


Dave the turning cowboy

turning wood into art

I think you are getting confused between the liquid product and the final hardened finishes and the MSDS sheets you refer to are for the liquid products.
The big dangers are when isocyantes are in vapour forms since they can damage eye and lungs but the dose required to affect someone by ingestion or absorption via the skin is much higher.

The final hardened finish uses up the cyanide in what is called a polymerisation process and very little free cyanide remain behind
Some polyurethane foams still have some free isocyanates but my understanding is you would have to eat kg of the stuff to be affected.
Hardened polyurethane has much less free cyanide than foams and such a low toxicity that you could quite safely eat from week old polyurethane crockery.
The older it gets, the less remains. Sanding hardened polyurethane is thus about a dangerous as sanding wood.

Burning polyurethane produces carbon monoxide, and trace amounts of nitrous oxide and hydrogen cyanide.
The risk is far greater that you will be asphyxiated by the CO before you will be hurt by the trace amounts of cyanide.

BTW I have suffered from a case of isocyanate poisoning - this and apart from the fact that I know some chemistry is how I know something about it.

The way I poisoned myself was I was 2-packing the kitchen counter top using a cheap paintbrush and cheap plastic gloves. The paintbrush kept dropping bristles and have you ever tried picking up bristles wearing a pair of floppy plastic gloves? In the end I gave up and took the gloves off and used my fingers. About 15 minutes after I finished the counter top I noticed a tingling sensation in my finger tips, lips and tongue. I knew what it was right away because I also like really hot chillis and have suffered the same effect from eating super hot chillis (it's an overdose of capsicin ) I got onto the MSDS and the Poisons hotline and they did the same (i.e. looked up the MSDS) and they said no worries, you can't die by skin absorption or ingestion unless you bathe in it or drink a few hundred ml of the liquid. Within two hours the symptoms had gone and I was OK.

Have since recoated the bench top several times with the same stuff with no ill effects.

Bottom line is be careful with the liquid but don't sweat the hardened product.

Originally Posted by BobL

I think you are getting confused between the liquid product and the final hardened finishes and the MSDS sheets you refer to are for the liquid products.
The big dangers are when isocyantes are in vapour forms since they can damage eye and lungs but the dose required to affect someone by ingestion or absorption via the skin is much higher.

The final hardened finish uses up the cyanide in what is called a polymerisation process and very little free cyanide remain behind
Some polyurethane foams still have some free isocyanates but my understanding is you would have to eat kg of the stuff to be affected.
Hardened polyurethane has much less free cyanide than foams and such a low toxicity that you could quite safely eat from week old polyurethane crockery.
The older it gets, the less remains. Sanding hardened polyurethane is thus about a dangerous as sanding wood.

Burning polyurethane produces carbon monoxide, and trace amounts of nitrous oxide and hydrogen cyanide.
The risk is far greater that you will be asphyxiated by the CO before you will be hurt by the trace amounts of cyanide.

BTW I have suffered from a case of isocyanate poisoning - this and apart from the fact that I know some chemistry is how I know something about it.

The way I poisoned myself was I was 2-packing the kitchen counter top using a cheap paintbrush and cheap plastic gloves. The paintbrush kept dropping bristles and have you ever tried picking up bristles wearing a pair of floppy plastic gloves? In the end I gave up and took the gloves off and used my fingers. About 15 minutes after I finished the counter top I noticed a tingling sensation in my finger tips, lips and tongue. I knew what it was right away because I also like really hot chillis and have suffered the same effect from eating super hot chillis (it's an overdose of capsicin ) I got onto the MSDS and the Poisons hotline and they did the same (i.e. looked up the MSDS) and they said no worries, you can't die by skin absorption or ingestion unless you bathe in it or drink a few hundred ml of the liquid. Within two hours the symptoms had gone and I was OK.

Have since recoated the bench top several times with the same stuff with no ill effects.

Bottom line is be careful with the liquid but don't sweat the hardened product.

That's very reassuring, Bob. I always thought that poly was pretty well inert when hardened.
I know little or nothing about chemistry, and was reacting to rustynail's statement in the other thread that it should never be burnt off due to the hydrogen cyanide fumes that are produced.
Personally, I'd never burn anything off anyway, poly or otherwise. I'd be concerned about carcinogens in smoke more than anything else.

I always apply the water-based WOP without gloves, though. Perhaps I'd better start wearing them.

Edit: I just burnt the poly off a scrap I prepared yesterday and didn't get the blue flame that I was warned about, either - just a normal yellow flame.

The other confusion I noticed here is that you refer to POLY urethane. As Bob already mentioned, it is harmless once dry and has so little - if ANY isocyanides in it ot be irrelevant.
The MSDS you are worried about has the following statement in it (because it too has no free or evaporating isocyanides only pre-polymer liquid ones which polymerise and are then bound): Based on available information, not classified as hazardous according to criteria of Safe Work Australia; NON-HAZARDOUS SUBSTANCE

However two-pack URETHANE is a different story! Every can of two-pack has a big warning about isocyanites on it - except the very new ISO-FREE Urethane finishes. Spraying the former is a very risky business with proper protective gear and ventilation.

Don't worry about Estapol etc - not even their 2-pack POLYurethane.

PS: Have a look at the chemical that is Superglue....

Originally Posted by jhovel

The other confusion I noticed here is that you refer to POLY urethane. As Bob already mentioned, it is harmless once dry and has so little - if ANY isocyanides in it ot be irrelevant.
The MSDS you are worried about has the following statement in it (because it too has no free or evaporating isocyanides only pre-polymer liquid ones which polymerise and are then bound): Based on available information, not classified as hazardous according to criteria of Safe Work Australia; NON-HAZARDOUS SUBSTANCE

However two-pack URETHANE is a different story! Every can of two-pack has a big warning about isocyanites on it - except the very new ISO-FREE Urethane finishes. Spraying the former is a very risky business with proper protective gear and ventilation.

Don't worry about Estapol etc - not even their 2-pack POLYurethane.

PS: Have a look at the chemical that is Superglue....

Thank you for this Joe. I'm feeling much happier about using polyurethane after both your's and Bob's responses.

I'll continue to eat it for breakfast, lunch and dinner now.

On a similar tack, I had a read of the label on a bottle of Gorilla Glue earlier. It has a warning about diisocyanate, and a further warning that it should be avoided by individuals with chronic asthmatic conditions. I've never actually opened and used this bottle, and probably never will. I have emphysema. Not quite chronic asthma, but still.....

I won't bother downloading the cyano-acrylate MSDS, but I can imagine!

The most significant message in all of this is follow the current level of knowledge and to know what you are dealing with and observe the recommendations for storage and use.

The MSDS and technical information supplied by the manufacturers/suppliers contains that info but it is rarely read by most users of the product.

In many cases the storage of the product or its by products present some of the highest risks to the user. Hazards like being overcome by vapours, & solvent flammability in use present far more significant risks than someone possibly burning off the end product. Some well known turners have been observed to “flash off” alcohol used as a solvent in dyes during demonstrations. High risk in most workshops. The risk is greater in smaller workshops that we often see.

Inappropriate use or storage of products often directly beside another highly incompatible chemical or near another hazard (naked flame) creates a very significant risk.

By products and mixed chemicals as in the recent case of the mixed epoxy may generate considerable heat, enough to start a fire etc.

I am aware of an inquiry into the injury of a Fire Fighter in Vic where the ignition source was an excessive build up of nitrocellulose laquer overspray that had been “fuming” for days before the fire service was called in – unfortunately way to late. “Who entered the factory to investigate a smouldering fan had no idea of the dangers that lay inside (no Hazchem signage). A flash fire erupted in a spray booth, where lacquer containing nitrocellulose had been used for polishing rice-paper screens“. http://www.heraldsun.com.au/news/vic...-1225909145735

Yes, reading those data sheets, even they indicate that the biggest concern is inhaling the mineral turpentine in the oil-based polys.

I got a reply from MinWax, but they seem to have misinterpreted my use of the word 'old'.

From my query:
This relates to the possibility of Hydrogen Cyanide being released in possibly dangerous quantities if a blowtorch is used to remove old polyurethane.
Thank you in advance for any further information you can give me on this subject.

And their reply:
Dear Steve,
I honestly do not know about older polyurethanes. I am not sure if any contained cyanide. Our products have not.
Regards,
Craig
Minwax Product Support

Not to worry, they still make their point - nothing to worry about.
Overall, I just wasted heaps of time going in a great big circle. That's what I learned from this.

Originally Posted by Hermit

Yes, reading those data sheets, even they indicate that the biggest concern is inhaling the mineral turpentine in the oil-based polys.

I got a reply from MinWax, but they seem to have misinterpreted my use of the word 'old'.

From my query:
This relates to the possibility of Hydrogen Cyanide being released in possibly dangerous quantities if a blowtorch is used to remove old polyurethane.
Thank you in advance for any further information you can give me on this subject.

And their reply:
Dear Steve,
I honestly do not know about older polyurethanes. I am not sure if any contained cyanide. Our products have not.
Regards,
Craig
Minwax Product Support

Not to worry, they still make their point - nothing to worry about.
Overall, I just wasted heaps of time going in a great big circle. That's what I learned from this.

Certainly not time wasted. Your knowledge (& ours) of the product is much higher than when you started plus we all have learned a little more about other hazards in using these products.

it is easy to get caught up in single particular obscure hazards.

The fact is we need to be cauefull about all fumes associated with all finishes......even good old shelac made from bettle $h!% and straight forward alcahol can do you plenty of damage.

ventilate ventilate ventilate.

and as far as burning paint off.......hell.....you have to assume that any paint you you may burn could make you very crook......realy there has to be a better option.

cheers