carries glass fragments of the envelope with it. Once these fragments reach the center of the tube, they
continue outward with considerable velocity. The result is similar to an explosion, in that the immediate
area surrounding the electron tube is filled with fast-moving glass fragments. You, as a nearby object,
may find yourself the target for many of these glass fragments. For this reason you should handle all
electron tubes with care.
CATHODE-RAY TUBES (CRTS)
Since most electron tubes are small, the possibility of them being a safety hazard is usually very
small. There are two exceptions to this: CRTs and radioactive tubes.
The glass envelope of a CRT encloses a high vacuum. Because of its large volume and surface area,
the force exerted on a CRT by atmospheric pressure is considerable. The total force on a 10-inch CRT
may exceed 4,000 pounds. Over 1000 pounds is exerted on the CRT face alone.
When a CRT is broken, a large implosion usually occurs. Almost two tons of force hurl glass
fragments toward the center of the tube. At the same time, the electron gun is normally thrown forward
inside the tube. The face, because of its size, tends to move very slowly toward the center of the tube.
This presents one of the main hazards of a broken CRT. The electron gun passes through the center of the
tube with considerable force. It continues until it strikes the CRT face. The impact from the electron gun
normally breaks the CRT face into many small fragments, which are hurled outward. The face is coated
with a chemical coating that is extremely toxic. If you are unfortunate enough to experience an accidental
implosion of a CRT and are nicked by one of these fragments, seek immediate medical aid. As you can
see, improper handling of a CRT can be very hazardous to your health.
The CRT is, in essence, a tiny fragmentation bomb. The major difference between a CRT and a
bomb is that a bomb is designed to explode; a CRT is not. As long as you handle a CRT properly, it
represents no danger to you. Only when you mishandle it do you risk the danger of being pelted with an
electron gun and toxic glass fragments. When handling a CRT, you should take the following precautions:
1. Avoid scratching or striking the surface of the CRT.
2. Do not use excessive force when you remove or replace a CRTs deflection yoke or socket.
3. Do not try to remove an electromagnetic-type CRT from its yoke until you have discharged the
high voltage from the CRTs anode connector (hole).
4. Never hold the CRT by its neck.
5. Always set the CRT with its face down on a thick piece of felt, rubber, or smooth cloth.
6. Always handle the CRT gently. Rough handling or a sharp blow on the service bench can
displace the electrodes within the tube, causing faulty operation.
7. Wear safety glasses and protective gloves.
One additional handling procedure you should be aware of is how to dispose of a CRT properly.
When you replace a CRT, you cannot simply throw the old CRT over the side of the ship, or place it in
the nearest dumpster. When thrown over the side of a ship, a CRT will float; if it washes ashore, it is
dangerous to persons who may come in contact with it. A CRT thrown in a dumpster represents a hidden
booby trap. Therefore, always render the CRT harmless before you dispose of it. This is a fairly simple
procedure, as outlined below.
Note: Be sure to wear safety goggles.