The powder is Phosphor coating. It is used because when an electron beam hits it, it glows. I have read multiple reports, most of which say it it not toxic, but you should not breath the powder. Phosphor is used in a lot of other things, most commonly fertilizer. You wouldn't want to breath that stuff, but it is safe to use it on your grass. I use the glass out of old computer monitors. What I do after I break them open is to clean them out with a water hose, something like Ajax and one of those green scrubbers. I clean them out in the middle of my yard. Just take care not to spray water on it to fast in order to keep the dust down. Once you scrub them out real good, they are good to go. The biggest heath warning associated with CRT screen or TV screens is the lead contained in the glass. Why do you think TV's are so heavy? One of the reasons is all the lead in the glass. It is the lead in the glass that make throwing away old TV's so difficult. I wouldn't let young kids around if you are napping TV glass. So basically, don't breath the dust and don't eat the glass and you should be OK.
