Can dust build-up in Time Capsule (vertical model) be a fire risk (or other risk)? Saw dust built up at the bottom vent of the Time Capsule (vertical model). Blew air in it to extract the dust from the other side of the vent. However I then noticed that some went back inside the unit (had the TC upside down for this).
After some research to see how it's made inside, I saw that there is 2 areas, one for the wifi components and one with the fan unit attached to the power supply.

I can't open it to clean it (no tools, no expertise).

My question: If some dust patches went inside near the wifi board or near the fan/power supply area, is this a risk for fire or any other risk ? Or is general dust build up in a computing unit not a concern in general ?
In terms of being a fire risk, no, dust building up inside a Time Capsule is not a concern.

Depending on the hardware, dust can be a concern for other reasons. In the early days of computing when floppy disks were the main storage medium, we used to have a saying that getting dust onto the disk was like running into a brick wall - not good at all.

However, I have worked on countless computers over the past three decades and they're usually full of dust inside (well, in tower models at least). None of these machines have ever caught fire. 

With regard to a Time Capsule, they do not generate a lot of heat - much less than a computer with multi-core processors doing some heavy processing tasks. So you can rest easy.