El-Hasan concurred and said it’s best to keep a filter in the one or two rooms where you spend the most time, such as an office or bedroom, and to keep doors and windows closed.

The rays of the evening sun shining above Burundi’s main city, Bujumbura, filter in.

In the camera settings, check the “macro control” option and make sure this mode is not enabled if you’re using a filter in front of the lens or you’re putting your phone up to a telescopic eyepiece.

That zone also serves as a filter in which chemical processes and microbes reduce the toxicity and mobility of metals.

As people filter in, make name tags and find seats on the assorted furniture, some sit by themselves while others start up soft-spoken conversations.