I remember the first time I had to wear an air pack and facemask.
My foreman asked me to clean debris from the floor of an empty storage tank that contained fumes. When I put the facemask on, I immediately felt uncomfortable and isolated. I was very aware of my breathing due to the noise made by air coming into the facemask and my breath exiting the mask. The cylinder of air hanging on my back felt really heavy and made it hard to bend over.