Why does air smell different after using a CPAP machine?

[DaveC426913]

TL;DR Summary

I think it smells like burnt sintered steel filings.

I've recently started using a CPAP machine, which filters air and pumps it through a water chamber to humidify it.

After a night of sleeping with it, I take it off in the morning and, once I breathe normal air, it has a very strong and distinctive smell. To me, it smells like something metallic and burnt (I don't know what "sintering" is off hand, but I fancy this is what it smells like).

The astronauts that visited the Moon described the smell as like "burnt gunpowder", which is as good a description as mine. Maybe they were just smelling regular air?

Thanks to ActionLabs, I know that that water has a taste. So maybe air has an odour.

 

[BillTre]

We rapidly become acclimated to many oders. After an initial exposure will not notice them much. This could be some of this effect.
Exposure to the specific chemicals in your CPAP output might also affect this. They might be in some sensory competition or interact with other smell sensations in some manner.

Sintered metal is powdered metal being compressed and heated to melt it together into a single metalic mass.

 

[DaveC426913]

We rapidly become acclimated to many oders. After an initial exposure will not notice them much. This could be some of this effect.

Yes, that's what I'm assuming is happening. And further supposing that the smell I smell once taking it off is the new smell of air before I become re-acclimated.

 

[Ygggdrasil]

Maybe that the smell is produced by running the CPAP machine (which gets exhausted to the room but not to the user).

 

[JT Smith]

You're breathing air through the CPAP machine. If air smells you'd smell it then.

Maybe it's time you vacuumed the carpet.

 

[berkeman]

Summary:: I think it smells like burnt sintered steel filings.

After a night of sleeping with it, I take it off in the morning and, once I breathe normal air, it has a very strong and distinctive smell. To me, it smells like something metallic and burnt

Were you wearing a Covid mask when you smelled it? I was once puzzled why my whole area at work smelled like chocolate. Turns out that I had spilled a couple crumbs of chocolate in my mask when having a snack at work before I put it back on.

 

[DaveC426913]

Were you wearing a Covid mask when you smelled it?

Not in my own home, no.

 

[DaveC426913]

You're breathing air through the CPAP machine. If air smells you'd smell it then.

The assumption is that the CPAP's filter is filtering something out.

Yeah, I guess you've actually got a point. Whatever it's filtering out isn't air, rather it's some contaminant.

 

[JT Smith]

Maybe. But then question is why don't you smell that contaminant when you go into the room after being away for a long time. Unless your theory is that all unfiltered air smells like burnt steel.

I wonder if it's possible that your CPAP machine is introducing an odor that you become accustomed to during the night. Could the absence of an odor after you've adapted to it be perceived as some other odor?

Maybe you can move your machine to some other location for a night or two?

 

[DaveC426913]

Maybe. But then question is why don't you smell that contaminant when you go into the room after being away for a long time. Unless your theory is that all unfiltered air smells like burnt steel.

Not theory ... conjecture maybe.

That's why I included the "water has a taste" video from ActionLab. Because water does have a taste - once we stop being accustomed to it.

 

[BillTre]

i can definitely smell water on a dry day.
The amount of water (humidity) in the air affects smells. Carbon dioxide has a much stronger smell in a humid atmosphere (like in a tissue culture incubator). Maybe it combines with the water to make acid.

 

[Tom.G]

Maybe it's the (overheated) motor in the CPAP machine that you are smelling.

 

[256bits]

Water would be 'activating' the aromatic compounds that have settled onto the dryer nasal passages.
You can not smell as well in dryer conditions.

 

[256bits]

Just so I don;t get asked
https://link.springer.com/article/10.1007/s00405-007-0446-2

Abstract​

The present study aimed at investigating the question whether olfactory function changes in relation to barometric pressure and humidity. Using climate chambers, odor threshold and discrimination for butanol were tested in 75 healthy volunteers under hypobaric and hyperbaric, and different humidity conditions. Among other effects, olfactory sensitivity at threshold level, but not suprathreshold odor discrimination, was impaired in a hypobaric compared to a hyperbaric milieu, and thresholds were lower in humid, compared to relatively dry conditions. In conclusion, environmental conditions modulate the sense of smell, and may, consecutively, influence results from olfactory tests.

 

[DrDu]

How about
https://en.wikipedia.org/wiki/Geosmin

 

[DaveC426913]

How about
https://en.wikipedia.org/wiki/Geosmin

Well-acquainted with the smell of beetroots and post-rainfall. (Although, I'd always assumed it was nitrates/nitrites. Aquaria have the same smell as nitrates/nitrites are part of the bacterial cycle.)

 

[DaveC426913]

Update: discovered that the effect remains even when disconnected from the machine.

When I got up in the middle of the night, I detached the (6ft plastic) hose from the mask, leaving me wearing just the mask.

The mask is made of soft silicon and only covers my nose, it has its own 6 inches of silicon hose, but does not have any kind of filter - I'm directly breathing air.

No smell detected.

So, as an experiment, I doffed the mask, and lo! the smell hit me.

That pretty much confirms that the phenom must be directly related to the silicon mask itself.

So: no smell when breathing through silicon, but smell detected when not breathing through silicon.

 

[rlaferla]

How do you clean your mask, tubing and humidifier? Do you use distilled water in your humidifier tank? When was the last time you changed the tiny filter on the machine?

 

[DaveC426913]

How do you clean your mask, tubing and humidifier? Do you use distilled water in your humidifier tank? When was the last time you changed the tiny filter on the machine?

With warm water and a bit of soap.
Yes, distilled water.
The machine is new.

Update 2:the effect does not need time for me to "get used to" anything. I put the mask on for ten seconds and pulled it off again and still smelled the gunpowdery smell.

I am beginning to suspect it's something totally dumb like it's just what the head strap smells like. (which would be in proximity to my face every time I remove the mask).

 

[trainman2001]

How can we get an air sample that hasn’t touched any thing/surface where an odor could be acquired? The CPAP example is not a good one because the filter, ducting and fan all could contribute molecules to the air stream. Pure demineralized water has very little taste. It’s the dissolved stuff that makes it taste.

 

[DaveC426913]

The CPAP example is not a good one because the filter, ducting and fan all could contribute molecules to the air stream.

Except the smell is present when the stream has been off for 12 hours.

 

[Tom.G]

Since this thread is still alive, I drafted Google for some leads.
(http://www.google.com/search?&q=what+materials+smell+like+gun+powder)

The findings reminded me that a component of gunpowder is Sulfur.

Many household soaps contain Sulfur based compounds (sulfanamides) as an antibacterial and antifungal.

That said, try using a different soap for cleaning the machine. (and read the list of ingredients)

Cheers,
Tom