CRT Displays Dangerous

[Ian.M]

CRTs don't explode, they implode.   The problem with early TV CRTs and many scope CRTs  was they didn't have a reinforced faceplate and a steel rimband to prevent it fracturing catastrophically, so any scratch or impact could possibly crack the tube neck launching the base and gun assembly straight through the screen, showering the viewer with high velocity glass and metal shrapnel if the toughened glass or plastic implosion protection shield was missing.   

Damage to the rear of a modern tube that doesn't compromise its faceplate rim is almost always far less dramatic, though any time you are handling glass under vacuum, safety glasses should be worn.

[Gyro]

I always thought that the purpose of the implosion protection band was to hold the base of the curved face of the CRT in compression (a bit like the chain around the dome of St Pauls Cathedral) to prevent it from imploding under a heavy front impact. I don't think it would have any effect on internal components being projected into the rear of the screen. In that case all the heavy glass of the cone is domed outwards too and the neck components are relatively low mass.

I've never seen a flat faced oscilloscope CRT with a protection band. They're always required to have a front plastic shield fitted (according to the Tek manual anyway).

[basinstreetdesign]

When I was a kid of about 14 in the '60s our B&W TV died and we had to get a new one.  This was a big deal for us.  A new TV was an event that ranked just short of buying a “new” car.  This was exciting enough but when it arrived they then gave me what was probably the best present I have ever received and it wasn’t even Christmas.  I got the old TV (sans picture tube) to do with as I pleased.  This was, to me, the next best thing to money.  In fact it was better than money since if I had any I wouldn’t know what to do with it and probably would have wasted it on junk food or comic books.  No, with the old TV I could take it apart and wonder what each of the diverse and strange pieces did and how.

As I said, I did not get the entire TV.  The picture tube I was not allowed to touch.  It was known to be dangerous, and rightly so, at that time.  Disposing of it fell to the capable hands of my bigger brother, Bob, nine years my senior who was deemed more worldly wise than I since he was already working at a steady job and making his own money.  He had already taken a course in electricity and electronics in high school and so was assumed to be more expert than I when it came to this kind of stuff.  In those days picture tubes were not made as they were later with an inch and a half of resin covering the display surface as a safety measure to prevent implosion or to protect one from it.  The sets themselves were built with a sheet of tempered window glass fixed to the front of the cabinet in front of the picture tube so that should the worst happen then the glass shards would probably not come through the front of the set to dice us all.  I was later to find out, in fact, that tube implosions during handling at the factory where they were made were then not uncommon.  The manufacture of picture tubes was not as automated as later on so they were handled by people at several stages during their assembly with the inevitable spectacular failures due to weaknesses in the glass falling susceptible to the odd bump.  I do not know what the casualty rate was for those in those jobs nor do I know if they got extra danger pay.  They should have.

Bob wrapped it in a couple of my dads’ old WW II army blankets and set it into a cardboard box in the trunk of our old ’55 Chevy for the trip to the dump.  Dad drove with Bob in the front seat and me in the back as I would be hanged if I didn’t come to see the action.  The tension was palpable.  The trip was slow as we all felt as though we were a transporting a nitro-glycerin bomb.  After lifting it out of the trunk and placing it gingerly face-down in the middle of the trash heap without its protective blankets we scurried back to take refuge behind a pile of garbage some eighty feet away.  Bob hoped that this would be far enough away to save us should the dump be rocked by the explosion we felt must surely come.  We were not to be disappointed.  Then choosing a moment when we were sure there were no passers-by within shrapnel range, Bob heaved a pop bottle at it and at once we were answered by a loud bang and the sound of a million pieces of glass which shot straight up ten or twenty feet and came straight down to the place it just departed.  If Bob was nonchalant, then I, at least, was relieved that we survived to go home and tell the tale.

[Nozzer]

My monitor proclaims (on an internal panel) that it produces something like 0.5uSv/hr of x-ray output; somewhere around background radiation.  Most CRTs should have similar performance, but I suppose you could always find an unlucky brand:

Tim

Tim, to put that radiation in to some context, when I was at secondary school in the early 1970s you could still buy uranium IV oxide to make up stunning red, orange and yellow glazes, and it was far cheaper to buy than the inferior selenium oxide (5g of selenium cost £5, whereas 100g of uranium oxide cost me 99p). I used to make it up in a blue plastic bucket with a wooden stick to stir and then dipped my pots in by hand, with no protective gear on whatsoever. I'm still going strong and have never suffered from any radiation related cancers. If uranium oxide were available today I would still happily use it, but sadly it is deemed too dangerous these days.