3 ms·

I was curious, so looked this up, but I have no prior knowledge of this: https://en.wikipedia.org/wiki/Brake_cleaner https://en.wikipedia.org/wiki/Brake_cleane

I was curious, so looked this up, but I have no prior knowledge of this: https://en.wikipedia.org/wiki/Brake_cleaner https://en.wikipedia.org/wiki/Brake_cleaner > Chlorinated brake cleaner containing tetrachloroethylene will, on exposure to high temperatures (above 500 °F (260 °C)) or strong UV light, decompose into phosgene and hydrogen chloride, both of which are extremely dangerous if inhaled So C2Cl4 - https://www.chemspider.com/Chemical-Structure.13837281.html https://www.chemspider.com/Chemical-Structure.13837281.html Oh, and this answer suggests that the reaction occurs with 'singlet' oxygen - https://chemistry.stackexchange.com/questions/76185/what-is-the-mechanism-behind-the-formation-of-phosgene-from-tetrachloroethylene https://chemistry.stackexchange.com/questions/76185/what-is-... (very pretty picture of the intermediates!)

hilbert42 3y ago
Thanks for that. Yeah, upon thinking it stands to reason that tetrachloroethylene aka PERC is used as a brake cleaner—once the cleaner would have contained carbon tet. PERC has replaced CCl4 in drycleaning too as it's safer. Note it too has a similar odor to CCl4 — note my previous comment to kragen. My opinion nowadays is to avoid inhaling the vapors of or exposing one's skin to any of these volatile cleaners, paint thinners etc. whether they're chlorinated hydrocarbons or not. Just assume them all to be dangerous. Incidentally, the problem with chlorinated hydrocarbons turning into phosgene has been known for a century or more. I find it very strange that this info isn't an essential part of all trades training where such chemicals are likely to be encountered. (I've been whingeing on HN previously about the inadequate and inappropriate training of the GP in chemistry. Yes, we teach chemistry at highschool as if everyone was going to progress to a degree in chemistry—such training is quickly forgotten if one doesn't become a chemist. We need to teach everyone about chemistry and how to handle chemicals they encounter in daily life and the likely dangers they pose.)
- cduzz 3y ago
  I was at an auto parts store last year and bumped into an ex-co-worker who did the "24 hours of lemons" style $500 race car thing. He was getting a bunch of brake cleaner (chlorinated stuff) and was talking about welding. I asked him and indeed he used brake cleaner to clean stuff he's planning on welding. I told him about the Phosgene gas issue and recommended he not clean the parts with that specific kind of brake cleaner... Anyhow, it's apparently not widely known to be as dangerous as it is, or perhaps people are just really lucky.
  - hilbert42 3y ago
    All agree it's a problem, but from these discussions it's not clear how serious it is on a per capita basis. If it's just an incident or two in millions then perhaps the problem isn't as bad as it's being made out to be (despite my multiple posts here about the matter and its dangers). Look at it this way: all of these chlorinated hydrocarbons are highly volatile solvents, it only requires a few minutes in air for the solvents to evaporate. Similarly, liquid residue solvents in hidden away places such as in tubes etc. will be vaporized to gas with just a little heat and then forced out of the tubes leaving only a minuscule amount of remaining vapor. That should be the situation long before the solvents are broken down by the heat. It would be informative to know the exact circumstances in the cases where phosgene was generated to the extent of causing injury. From my own experience in cleaning stuff with volatiles and then applying heat such as welding, I have difficulty in seeing how sufficient phosgene would be generated to cause harm. I say that as someone who, when young, suffered a minor degree of cyanide (HCN) poisoning when doing photograpic processing in a sealed-off bathroom without ventilation, so since then I've been highly attuned to situations where toxic gasses are likely to build up (I previously mentioned this incident on HN ages ago). Another incident: while not quite as dangerous as escaped phosgene, I had a vaguely similar incident when moving an old refrigerator sealed unit inside a shipping container full of other junk that made egress rather difficult. We broke a copper tube which released copious amounts of sulfur dioxide refrigerant and we couldn't get out quickly and thus suffered the consequences without too much drama. Right, SO2 isn't phosgene but there's was a damned side more of it here than I could ever envisage chlorinated hydrocarbons remaining after cleaning brakes (and one wouldn't do that in an enclosed space such as a shipping container)! All that said, there is absolutely no excuse for all containers of volatile cleaning agents to not have large red warnings about the potential for phosgene to be generated in the presence high heat and to do the cleaning and welding in a well ventilated place (like outdoors)—and to ensure that all fluid has fully evaporated before welding, etc. I'm not up to date on current cleaing products but I'd be surprised if there wasn't already a warning on them. If not, then the regulators have either lost the plot or have been grossly negligent.
    - cduzz 3y ago
      I thought that the phosgene was created by UV and heat, not just heat; so hitting the area with a torch first might make it safer? I'm going to put that in the "best not to find out" category of adventure.

hilbert42 3y ago

Thanks for that. Yeah, upon thinking it stands to reason that tetrachloroethylene aka PERC is used as a brake cleaner—once the cleaner would have contained carbon tet. PERC has replaced CCl4 in drycleaning too as it's safer. Note it too has a similar odor to CCl4 — note my previous comment to kragen. My opinion nowadays is to avoid inhaling the vapors of or exposing one's skin to any of these volatile cleaners, paint thinners etc. whether they're chlorinated hydrocarbons or not. Just assume them all to be dangerous. Incidentally, the problem with chlorinated hydrocarbons turning into phosgene has been known for a century or more. I find it very strange that this info isn't an essential part of all trades training where such chemicals are likely to be encountered. (I've been whingeing on HN previously about the inadequate and inappropriate training of the GP in chemistry. Yes, we teach chemistry at highschool as if everyone was going to progress to a degree in chemistry—such training is quickly forgotten if one doesn't become a chemist. We need to teach everyone about chemistry and how to handle chemicals they encounter in daily life and the likely dangers they pose.)

cduzz 3y ago
I was at an auto parts store last year and bumped into an ex-co-worker who did the "24 hours of lemons" style $500 race car thing. He was getting a bunch of brake cleaner (chlorinated stuff) and was talking about welding. I asked him and indeed he used brake cleaner to clean stuff he's planning on welding. I told him about the Phosgene gas issue and recommended he not clean the parts with that specific kind of brake cleaner... Anyhow, it's apparently not widely known to be as dangerous as it is, or perhaps people are just really lucky.
- hilbert42 3y ago
  All agree it's a problem, but from these discussions it's not clear how serious it is on a per capita basis. If it's just an incident or two in millions then perhaps the problem isn't as bad as it's being made out to be (despite my multiple posts here about the matter and its dangers). Look at it this way: all of these chlorinated hydrocarbons are highly volatile solvents, it only requires a few minutes in air for the solvents to evaporate. Similarly, liquid residue solvents in hidden away places such as in tubes etc. will be vaporized to gas with just a little heat and then forced out of the tubes leaving only a minuscule amount of remaining vapor. That should be the situation long before the solvents are broken down by the heat. It would be informative to know the exact circumstances in the cases where phosgene was generated to the extent of causing injury. From my own experience in cleaning stuff with volatiles and then applying heat such as welding, I have difficulty in seeing how sufficient phosgene would be generated to cause harm. I say that as someone who, when young, suffered a minor degree of cyanide (HCN) poisoning when doing photograpic processing in a sealed-off bathroom without ventilation, so since then I've been highly attuned to situations where toxic gasses are likely to build up (I previously mentioned this incident on HN ages ago). Another incident: while not quite as dangerous as escaped phosgene, I had a vaguely similar incident when moving an old refrigerator sealed unit inside a shipping container full of other junk that made egress rather difficult. We broke a copper tube which released copious amounts of sulfur dioxide refrigerant and we couldn't get out quickly and thus suffered the consequences without too much drama. Right, SO2 isn't phosgene but there's was a damned side more of it here than I could ever envisage chlorinated hydrocarbons remaining after cleaning brakes (and one wouldn't do that in an enclosed space such as a shipping container)! All that said, there is absolutely no excuse for all containers of volatile cleaning agents to not have large red warnings about the potential for phosgene to be generated in the presence high heat and to do the cleaning and welding in a well ventilated place (like outdoors)—and to ensure that all fluid has fully evaporated before welding, etc. I'm not up to date on current cleaing products but I'd be surprised if there wasn't already a warning on them. If not, then the regulators have either lost the plot or have been grossly negligent.
  - cduzz 3y ago
    I thought that the phosgene was created by UV and heat, not just heat; so hitting the area with a torch first might make it safer? I'm going to put that in the "best not to find out" category of adventure.