How dangerous or lethal is HV in CRT devices?

[ebastler]

A teenager like me, back in 1991, [...]

Back in ye olden days, back when people had brains that were generally fully functional, and I’d think that generally no mollycoddled and dumbed down fools were in charge [...]

From teenager in 1991 to Statler & Waldorf just 30 years later -- that's what I call rapid progress...

[p.larner]

from starting messing around with vale radios etc at an early age maybe 5 or 6yrs old,when i was about 10yrs old my folks tv went south,it was there first colour set (very expensive then circa 1974),they asked me too look at it,well it had been unplugged and turned off for about 5 mins,i went to unplug the anode cap next thing i landed about 7 feet away on the other side of the room,i have had many clouts over the years but that one i remember as being the worst!.

[DavidAlfa]

Unless you have some heart disease, not really.
You won't get "stuck" like when touching mains AC, the current is just a few mA, the initial discharge will instantly trigger a nervous system reflex, before you even realise, just like when touching a hot plate.
If you ever get shocked by it, specially by the tube (Which is a capacitor itself), you will learn something, and never forget

[schmitt trigger]

As others have mentioned, the real danger is with the violent reflex motion after receiving a shock.

When I was an EE student I had a part time job at a local TV shop.

One day aligning the convergence and purity of a color TV, which I had powered up while I was manipulating the back controls. For this procedure I was really focused watching the CRT image’s reflection on a mirror. I touched an HV point, don’t know exactly what.
I sprang backwards, lost my balance and hit a vacuum-tube amplifier chassis with the back of my head. Since I broke several tubes with my skull, glass shards lodged deep in the skin, which had to be painfully removed before stitching me up.

This accident left a scar which 47 years later I still have.

[woofy]

Its an old thread,

but as others have said, not really lethal at all. The real danger is the reflex action in pulling your hand away and cutting yourself on the sharp chassis. I spent the first first half of my life as a TV engineer for a once national and now defunct company. Cut hands and lots of colourful metaphors is all I really got from it. The voltage in a colour tv was around 25kv but at a low current. It sparked and left a small burn point. Tv tubes make a fine high voltage capacitor, so it was essential to discharge it before changing the tube.

[DavidAlfa]

Really? OMG. I remember opening on of these with about 10-12. Felt the shock all they way up to the shoulder!

[p.larner]

anything thats high voltage and is anywhere near a cap i view with suspicion and keep clear of!.

[BrianHG]

I once touched the wrong place in my 37inch CRT TV while it was on and I was tuning a pot.  A jolt went down my arm like I never experienced before.  I had a numbing burning nerve pain along the length of my arm for an entire year.  I'm lucky to be alive...

[Nusa]

The bigger the tube the more dangerous the charge is. 40" is around the largest that was ever in consumer use. Those weighed about 300 pounds, which meant they were treated like an appliance for transportation and installation.

[p.larner]

deffo wouldnt want to piss on its anode cap !.

[EPAIII]

In my younger days one thing I always hated working on was TV sets. They all had CRTs back then. And I have been hit with the residual charge on the CRT a time or three. Not from a working flyback, but just the charge remaining on the tube after it was disconnected. It was wise to discharge it more than once. But those shocks were not too bad and I was OK in a few minutes if not immediately. The thing is, the consumer TVs were deliberately made with a limited current being available from the HV circuit. It only needed to energize the tube which was as much of an insulator for that HV as they could make it. Yes, they thought of consumer safety back in the 1950s.

BUT, one time I was working on a professional, broadcast quality TV video monitor. A color one. And it had about 35 or 40 KV on the tube, not the usually lower HVs of the consumer TVs. And probably capable of somewhat more current. In this incident it was ON and I was probing around the flyback circuit and got on the wrong pin. That full Voltage went through the plastic of the probe I was holding, in my hand, out my foot, and through my sock and shoe. I found the burned in, pin holes in both places. My foot, with sock and shoe was resting on a metal foot rest of the work bench, which was grounded. It must have passed through at least a half inch (2 cm) of insulating materials in addition to my body. I felt the effects of that one for three or four hours that day. I probably should have been checked out by medical personnel, but I was young and indestructible. Today, with my 79 year old heart, it would probably kill me.

So, dangerous? Yes, and no. For the most part no. But it could be dangerous or even fatal under the right circumstances. And definitely NO FUN!

Edit: So ...

Been there,
Done that,
And didn't get the tee shirt.

I wonder if I could get one printed; "I survived 40,000 Volts!"

Not many people can say that, can they?

[Psi]

The real danger comes from the tube itself

+1 for this.  The tube is a large capacitor,  HV + Capacitor = danger.

[dazz1]

As I remember it, those CRT anode potentials were indeed dangerous.  For color TV they were up in the 25 kV range.  It doesn't take much capacitance to store a lot of energy at those potentials.  And energy is what can get you.  Any voltage above around 100V will cause conduction of human tissue, enough to cause problems.  As for electrocution, I believe the old electric chairs were around just a few kV.

Hi
The upper "safe" limit is about 48VDC.  You see this applied in battery packs etc.  This reference https://burncenters.com/safety/the-short-term-and-long-term-effects-of-electric-shock-on-the-human-body/ states even 50V can be lethal.

Lots of things affect a person's conductivity.  One of them is fatigue, which chemically reduces body resistance and  increases the risk of doing something stupid.

I am super careful with HV.   Your first mistake could be your last.  I connect probes etc with power off.  If there is something I need to do with power on (eg probe something), I do a power off rehearsal of the actions first.   

[Shock]

Reminds me of this video. But seriously... "dangerous to lethal" sums it up perfectly.

[David Hess]

A CRT had a lot less HV capacitance than a mid sized van de Graaff. For an operating device it was probably less dangerous than mains, more likely to knock you off. On the other hand, it might knock you into a mains connection.

I measured some Tektronix CRTs and the post deflection acceleration connection had 10s of picofarads, and discharged rapidly.

I do not know about color television CRTs; they are much larger.