SAFETY

There are certain safety precautions you should follow when you work with or handle the special tubes covered in this chapter. We will examine these tubes and their associated precautions in the following sections.

ELECTRON TUBES

The average electron tube is a rugged device capable of withstanding the shocks and knocks of everyday usage and handling. However, they are not indestructible. You should remember that most electron tubes contain a near vacuum enclosed by a glass envelope. Because of this, the glass is under constant stress from atmospheric pressure. Any undue stress, such as striking the envelope against a hard surface, may cause the envelope to shatter, resulting in an IMPLOSION.

An implosion is just the opposite of an explosion. When the glass envelope of an electron tube shatters, the outside atmosphere rushes into the tube to fill the vacuum. As the air rushes into the tube, it 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: CRT's 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:

• Avoid scratching or striking the surface of the CRT.
• Do not use excessive force when you remove or replace a CRT's deflection yoke or socket.
• Do not try to remove an electromagnetic-type CRT from its yoke until you have discharged the high voltage from the CRT's anode connector (hole).
• Never hold the CRT by its neck.
• Always set the CRT with its face down on a thick piece of felt, rubber, or smooth cloth.
• 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.
• 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.
• Place the CRT face down in an empty carton and cover its side and back with protective material.
• Carefully break off the plastic locating pin from the base (fig. 2-29) by crushing the locating pin with a pair of pliers.

Figure 2-29. - Cathode-ray tube base structure.

Brush the broken plastic from the pin off the CRT base. Look into the hole in the base where the locator pin was. You will see the glass extension of the CRT called the vacuum seal. Grasp the vacuum seal near the end with the pliers and crush it.

This may sound a little risky but it isn't. The vacuum seal can be crushed without shattering the tube. Once the seal has been crushed, air will rush into the tube and eliminate the vacuum.

RADIOACTIVE ELECTRON TUBES

Another type of tube that can prove hazardous to you, if you handle it improperly, is the radioactive tube.

These tubes contain radioactive material and are used as voltage-regulator, gas-switching, and cold-cathode, gas-rectifier tubes. Some of these tubes have dangerous radioactive intensity levels. Radioactive tubes are marked according to military specifications.

Radioactive material is added to a tube to aid in ionization. The radioactive material emits relatively slowly moving particles. This should not worry you because the glass envelope is thick enough to keep these particles inside the tube. Therefore, proper handling is nothing more than ensuring that the envelope remains unbroken. If these tubes are broken and the radioactive material is exposed, or escapes from the confines of the electron tube, the radioactive material becomes a potential hazard.

The concentration of radioactivity in an average collection of electron tubes in a maintenance shop does not approach a dangerous level, and the hazards of injury from exposure are slight. However, at major supply points, the storage of large quantities of radioactive electron tubes in a relatively small area may create a hazard. For this reason, personnel working with equipment using electron tubes containing radioactive material, or in areas where a large quantity of radioactive tubes are stored, should read and become thoroughly familiar with the safety practices contained in Radiation, Health, and Protection Manual, NAVMED P-5055. Strict compliance with the prescribed safety precautions and procedures of this manual will help to prevent accidents, and to maintain a safe working environment which is conducive to good health.

The clean-up procedures listed below are based on NAVMED P-5055. Your ship or station may have additional procedures that you should follow. Be sure you are aware of your command's policy concerning decontamination procedures before you begin working on equipment containing radioactive tubes. Some important instructions and precautions for the proper handling of radioactive tubes are listed below:

• Do not remove radioactive tubes from their carton until you are ready to install them.
• When you remove a tube containing a radioactive material from equipment, place it immediately in an appropriate carton to prevent possible breakage.
• Never carry a radioactive tube in a manner that may cause it to break.
• If a radioactive tube that you are handling or removing breaks, notify the proper authority and obtain the services of qualified radiological personnel immediately.
• Isolate the immediate area of exposure to protect other personnel from possible contamination and exposure.
• Follow the established procedures set forth in NAVMED P-5055.
• Do not permit contaminated material to come in contact with any part of your body.
• Take care to avoid breathing any vapor or dust that may be released by tube breakage.
• Wear rubber or plastic gloves at all times during cleanup and decontamination procedures.
• Use forceps to remove large fragments of a broken radioactive tube. Remove the remaining small particles with a designated vacuum cleaner, using an approved disposal collection bag. If a vacuum cleaner is not designated, use a wet cloth to wipe the affected area. In this case, be sure to make one stroke at a time. DO NOT use a back-and-forth motion. After each stroke, fold the cloth in half, always holding one clean side and using the other for the new stroke. Dispose of the cloth in the manner stated in instruction 14 below.
• Do not bring food or drink into the contaminated area or near any radioactive material.
• Immediately after leaving a contaminated area, if you handled radioactive material in any way, remove all of your clothing. Also wash your hands and arms thoroughly with soap and water, and rinse with clean water.
• Notify a medical officer immediately if you sustain a wound from a sharp radioactive object. If a medical officer cannot reach the scene immediately, stimulated mild bleeding by applying pressure about the wound and by using suction bulbs. DO NOT USE YOUR MOUTH if the wound is a puncture-type wound. If the opening is small, make an incision to promote free bleeding, and to make the wound easier to clean and flush.
• When you clean a contaminated area, seal all debris, cleaning cloths, and collection bags in a container such as a plastic bag, heavy wax paper, or glass jar, and place them in a steel can until they can be disposed of according to existing instructions.
• Use soap and water to decontaminate all tools and implements you used to remove the radioactive substance. Monitor the tools and implements for radiation with an authorized radiac set to ensure that they are not contaminated.

As you can see, the cleanup that results from breaking a radioactive tube is a long and complicated procedure. You can avoid this by simply ensuring that you don't break the tube.

CONVENTIONAL TUBES

While conventional tubes present few safety problems, beyond broken glass and the possibility of cutting yourself, there is one precaution you must know. Namely, electron tubes are hot. The filaments of some tubes may operate at several thousand degrees. As a result, the envelopes can become very hot. When you work on electron tube equipment, always deenergize the equipment and allow the tubes sufficient time to cool before you remove them. If this is impossible, use special tube pullers which the Navy stocks for this purpose. Never attempt to remove a hot tube from its socket with your bare fingers.