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Author: Subject: Toxicity of phosgene
peach
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[*] posted on 3-1-2012 at 10:17


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The other danger of phosgene, in addition to its hydrolysis, is the fact that it is also a very strong acylating agent. The carbon centre is strongly electrophilic, and chloride is a very good leaving group, meaning that phosgene will readily add to any nucleophilic organic molecules (such as the bases in DNA). Not only will this lead to cell death in the short term, but in the long run you also have to worry about cancer.


Carbon monoxide can also enter the body entirely undetected and the only warning sign is of imminent death is feeling a bit sleepy, but the point in bold above is important:

"There are 2 mechanisms of injury, hydrolysis and acylation. In hydrolysis, damage caused by phosgene is due to the presence of a highly reactive carbonyl group attached to 2 chloride atoms. The gas dissolves slowly in water, but when this occurs, it hydrolyses to form carbon dioxide and hydrochloric acid. This slow dissolution allows phosgene to enter the pulmonary system without significant damage to the upper airways. However, in the lower airways and alveoli, the tissue undergoes necrosis and inflammation. After the first few hours of exposure, the carbonyl group attacks the surface of the alveolar capillaries, causing leakage of serum into the alveolar septa. The tissue fills with fluid, causing hypoxia and apnea. Massive amounts of fluid (up to 1 L/h) leak out of the circulation, leading to a noncardiogenic pulmonary edema, with associated hypoxemia and volume depletion.

Acylation involves the reaction of phosgene with nucleophilic moieties causing denaturation of proteins, changes in cell membranes, and disruption of enzymes.
The permeability of the blood-air barrier is altered, leading to interstitial edema, and the inflammatory cascade is activated. This primarily occurs in the bronchioli and alveoli since they are not protected by a mucous layer."


A member of our own forum died not too long ago as the result of an experiment involving phosgene.

Witness how even DuPont can get it wrong:

<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/ISNGimMXL7M" frameborder="0" allowfullscreen></iframe>

Rather than building an entirely enclosed and computer controlled storage room, another option they could have looked at would have been enclosing the cylinders in liners. Such that, if the cylinder began to leak, it would do so through the scrubber. That may have cost significantly less than $2.2M to implement. It would have also been easier to control the atmosphere around the cylinder it's self (keeping it dry), to prevent hydrolysis and subsequent corrosion caused by cylinder leaks. Temperature control would have been easier, allowing for better process control.

Any leak occurring would produce a more rapid build up of concentration within the liner due to the small volume for dilution, allowing a detector to pick up the early signs of failure.

Many of the cylinder companies supply cabinets for storing dangerous cylinders. A lot of these are vented at the top. If the cylinder begins to leak, it is exhausted through the vent.

A simple vented cabinet (a liner):


Note the vents attached at the top:


Here's the high tech GasGuard from Air Products (designed to not only store the cylinder and provide a safe venting, but also control the delivery via an in built computer). I would guess this one is from some form of semiconductor place given it has silane written on the front. An environment where precise control is required:


These liners are designed for one to three cylinders sat in a lab. For bulk work, as DuPont were doing, they could have built the liners themselves from large diameter HDPE pipe (or something similar), to save capital on the fancy paint job and pretty aesthetics.

The description of the burst hose doesn't make total sense. Unless they were cooling the cylinders, the phosgene in the hose would be at approximately the same temperature it was at under normal transfer conditions, and so a similar pressure. There is also an issue with the idea that the guy was looking at swapping them over knowing that the hose hadn't been correctly purged.

The only way that could be achieved without detaching the still full hose would have possibly been to stand it up (or otherwise get the dip tube out of the phosgene) and purge it.

Given the weight of them and length of the hoses, a more likely approach would have been to simply disconnect it.

Assuming they don't have flow stops on the ends of the hoses, that would entail exposure to the contents. He would have been partially exposed even if they did feature stops.

In other words, he should have had a suit on given the problem at hand. Lack of communication perhaps meant he didn't realise precisely what was going on.

I can offer two other possible causes for the accident (which could involve charges against DuPont if they were true):

- The video mentions the hoses being over exposed. PTFE may be slightly permeable with regards to phosgene, but how readily does phosgene actually alter PTFE? If hose age is the issue, it seems more likely the phosgene would permeate the liner and then attack the braid. But an alternative explanation is the hose being damaged by kinking and abuse, due to it dangling in mid air as heavy cylinders are being moved around. Note in the video at 9.25 that it appears someone has stuck something directly over the point where the hose ruptured, which is either pure coincidence or a previously damaged spot being covered.

- He was actually sprayed when he was told to unscrew the hose, not realising it was still full and under pressure, without a suit on.

[Edited on 3-1-2012 by peach]




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[*] posted on 5-1-2012 at 08:12


Interesting post. Poor guy :( Those tanks look scary as hell, no way I would be working on them without a suit

Would acyl chlorides have the same danger? They are supposed to be potent lachrymators so it wouldn't have the delayed effect. Alkylating agents would also have similar acute toxicity. How about acetic anhydride?




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[*] posted on 5-1-2012 at 10:26


Thanks for posting that, peach. I'm a fan of documentaries, and that was a very good one. Man, I'd be terrified working next to that much pressurized phosgene.
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[*] posted on 5-1-2012 at 15:06


Here I am learning to be a phosgene chemist, note the big smile on my face since it was one of my first days along with the phosgene cylinder to my left. Despite the danger of phosgene it still finds heavy use in industry since it is such a clean way to make isocyanates, carbamoyl chlorides, isonitriles, chloroformates, acyl chlorides, etc. The facility where this picture was taken is no longer in operation however from what I have seen of other places that use phosgene, enclosures around cylinders and additional safety measures aside from nearby escape masks are not used save in bulk use.

IMG_0076.jpg - 221kB




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[*] posted on 5-1-2012 at 19:31


BromicAcid, weren't you concerned about working with phosgene with no gas mask or hood?

I remember way back when some customers were complaining about a "smell of fresh mown grass" when using a copier with my employer's paper. We thought it might be phosgene released by the heat of the copier.

I've often thought that those hoses covered with braided steel give a false sense of security. They look so tough yet the only purpose of the steel braid is to protect the real hose inside from abrasion, and maybe kinking.




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[*] posted on 5-1-2012 at 19:37


Quote: Originally posted by BromicAcid  
Here I am learning to be a phosgene chemist, note the big smile on my face since it was one of my first days along with the phosgene cylinder to my left. Despite the danger of phosgene it still finds heavy use in industry since it is such a clean way to make isocyanates, carbamoyl chlorides, isonitriles, chloroformates, acyl chlorides, etc. The facility where this picture was taken is no longer in operation however from what I have seen of other places that use phosgene, enclosures around cylinders and additional safety measures aside from nearby escape masks are not used save in bulk use.



Holy Crap! I would have a huge smile on my face too!




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[*] posted on 5-1-2012 at 19:51


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BromicAcid, weren't you concerned about working with phosgene with no gas mask or hood?

Safety measures were in place, electronic phosgene monitor, dosimeter badge, and air hood present. Prior to running the apparatus is snoop checked to ensure its integrity. Also the add is atmospheric, the setup completely open to a scrubber so there is no potential for pressure buildup. The gas is only pressurized at the regulator. It is safer than it appears although when entering the hood (as I am about to do in the picture) standard practice is to don breathing air. Being new to the job I did not follow this.

With regards to the steel braided line we do not use them due to the DuPont accident. In the picture you see standard PE tubing coming from the regulator. This is so it can be inspected as needed, also since it is atmospheric the worry of it being under pressure is nill.

Edit: That whole apparatus is in a walk-in fume hood. You cannot see the doors though since they are open, it was about 20 feet long.

[Edited on 1/6/2012 by BromicAcid]




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[*] posted on 6-1-2012 at 07:53


Can you give us a hint to whats going on? Why do they have a reflux condenser and a distillation column? And its all Aldrich brand, expensive! I love the water jacketed distillation adapter



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[*] posted on 6-1-2012 at 11:20


What I like is what appears to be an air-driven mixer.

Bromic has the look of: "I can't believe they are paying me to do this."




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[*] posted on 7-1-2012 at 02:41


Quote: Originally posted by MrHomeScientist  
Thanks for posting that, peach. I'm a fan of documentaries, and that was a very good one. Man, I'd be terrified working next to that much pressurized phosgene.


The greatest risk is the one which we do not consider.

And yay, the dust did explode, mightily... Combustible Dust: An Insidious Hazard

Nice to see you there bromic, stay safe brah! :)




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[*] posted on 7-1-2012 at 06:45


Quote: Originally posted by BromicAcid  
The facility where this picture was taken is no longer in operation however from what I have seen of other places that use phosgene, enclosures around cylinders and additional safety measures aside from nearby escape masks are not used save in bulk use.
BromicAcid, was that picture taken at Carbolabs?
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[*] posted on 7-1-2012 at 07:49


Yup, nice to see you recognize the place still :D



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[*] posted on 7-1-2012 at 20:39


Why this needs it own thread I can't imagine given that the study of it ranks
second only to that of anesthesia , and online documentation is more than
you could possibly ever read.

See PHOSGENE AND DIPHOSGENE lower paragraph here page 257 ( seen at upper left corner of page ) & 258
http://history.amedd.army.mil/booksdocs/wwi/VolXIV/VolXIVhtm...

See page 311 ( seen at upper left corner of page ) here _
http://history.amedd.army.mil/booksdocs/wwi/VolXIV/VolXIVhtm...

Observe Exposure limits Section 3 here to become a fatal casualty
www.airgas.com/documents/pdf/006297.pdf

Should be noted that Phosgene is perceptibly and physiologically indistinguishable in action from
nitrogen dioxide - http://www.vlib.us/medical/HMSO/chapter7.htm#70 ,71 ,72 ,73

.
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[*] posted on 19-7-2012 at 13:23


We used to buy a lot of compounds from Carbolabs... They were bought by Aldrich, correct? I bet that was an interesting job. Almost as good as Columbia Organics or some other small organic companies.

When I was in graduate school the lab next door had a huge cylinder of Phosgene strapped to a bench NEAR the hood (not in it), with a tube running in to the hood. We also had bottles of 50% phosgene in toluene in the refrig. as well. It's a miracle that we did not have more accidents back then, as safety in universities was much less then today, and it is still much less then industry.
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