I have not owned a DreamStation machine so just guessing a bit. The source of noise is the fan. It runs at a variable speed to produce more and less pressure as required. This fan noise can travel upstream through the air filter and out the air inlet. It can also travel the other way with the air flow to the humidifier and to the mask hose. I suspect the inlet path is the more of a problem. So, they may line the ducting on the inlet with a sound dampening foam material. It would appear they chose a poor quality foam material for this purpose. Another possible but less probable area for foam would be in the seal between the machine and the humidifier. ResMed use silicone seals for this purpose. Not sure about the DreamStations.
From what I’ve heard from someone on the ASAP Board who used to manage a sleep lab, the foam IS, in the first instance, in a separate compartment. However, over time, or in the case of damage to the machine’s integrity, the seams in the machines can open up or gap, giving humidity (and in the case of the O3 sanitizers, ozone) access to the foam. That’s how the degradation can occur. And, yes, it was also apparently a poor choice of foam material. I’m not sure what kind of seals were used in the Respironics machines….
Here is a link to a Youtube video that steps through a process to remove the foam. Let me be clear. I do not recommend doing this. It looks like a butcher job to me. However, it does reasonably show where the foam is located in the machine. It is a painfully long video but if you look at 2-3 minute section starting at the 10 minute mark, you can see where the foam is located. From what I can see, the air is sucked in through the inlet filter, and down into an annular chamber that goes about half way around the outside of the fan. This chamber seems to have the foam at the top and possibly a space at the bottom for the air to flow through. I don't think the air actually flows through the foam, but it may. Once the air gets around it then goes into the suction of the fan. I would say it serves two purposes. One is to suppress noise that would make its way back to the inlet and come out the inlet filter. It may also dampen noise from the fan itself so it does not go out the side of the machine. It is clear that the inlet air either goes next to, or through the foam. So if there is toxic materials in the foam, then you would be breathing them in.
The bottom line is that I consider this foam removal a butcher job. Yes it does get rid of the foam, but for sure the machine will be much noisier. And, will it control pressure as well? Don't know.
just another note.while the air is passing over a chemical cocktail (foam) there is the possibility of this happening again. lab testing of foams to be used in these devices does not replace real life use. years of use may have different outcomes to short term lab tests. maybe engineers need to find a solution so this air/foam contact can be eliminated. have a look on you tube,there is a video showing the replacement foam,looks like polystyrene packing foam.i do not know to how add a link to the video.
I believe there are some which are claiming the deterioration of the foam may be caused by the highly advertised products like SoClean which uses ozone as the gas to disinfect the machine. Ozone is an extremely aggressive oxidizing agent and I think quite easily could attack a foam product. I believe all manufacturers recommend against using SoClean and the similar products which use ozone.
I doubt that we have to look far from the manufacturers when it comes to the degradation of foam products. It all seems to give off nasty fumes initially and eventually revert back to something like sand or crumble into fragments.
I think the verdict is still out when it comes to ozone.
I've used various ozone generators through the years in many different situations and never yet detected any real impact on anything beyond airborne particles and surface dust.
I used 4 commercial machines at one time to push the air in our living space to blue and kept it there for hours without discernible issues and that was with everything we own immersed in the ozone.
I regularly use ozone to eliminate odors and mold spores. There are many times that I wished that the achievable level of ozone was more aggressive but I fail to see it in real-life applications.
I think the main limitation in domestic applications and in most commercial applications is that the machines can only reach a certain concentration of ozone without a supply of pure oxygen.
Anyways I doubt that Phillips would recall their machines if it was not directly their fault.
I haven't seen or used an ozone CPAP cleaner and I certainly would not recommend one.
I understand why that report was cautious, especially with regard to people with allergies or asthma.
From my personal exposure, I would think that the level of risk is probably on par with using various cleaners or even persistent exposure to hand sanitizer.
It's likely that the long-term risks of domestic cleaning chemicals are actually worse, even without asthma or allergies.
We accept and surround ourselves with many potentially dangerous products.
Yet it's the new and unknown products that worry us the most.
As they should.