I’ve been there and done that. I forgot to close my 3way valve when I was filling a 20lb CO2 extinguisher and I emptied the CD50T cylinder quickly. One heck of a cloud and little bits of dry ice all over my scale and service counter. I had to wait for a couple of minutes for the cloud of CO2 to clear out of my shop before I could switch out cylinders and get back to work.
Steven