Warning Skipbreathing may lead to hypercapnia and shall not be practiced

Increased breathing resistance results from the design of the equipment and increased air density. For normal diving, a marked increase of breathing resistance should not occur until the primary air supply has been almost depleted. This increase in breathing resistance is a signal to the diver to activate the reserve air supply and to begin an ascent with the partner immediately. When equipped with a submersible bottle gauge, the diver shall monitor his air supply pressure and must terminate the dive whenever bottle pressure is reduced to 500 psi for a single bottle or 250 psi for a set of double bottles.

7-7.2 Mask Clearing. Some water seepage into the face mask is a normal condition and is often useful in defogging the lens. From time to time the quantity may build to a point that it must be removed. On occasion, a mask may become dislodged and flooded. To clear a flooded mask not equipped with a purge valve, the diver should roll to the side or look upward, so that the water will collect at the side or bottom of the mask. Using either hand, the diver applies a firm direct pressure on the opposite side or top of the mask and exhales firmly and steadily through the nose. The water will be forced out under the skirt of the mask. When the mask has a purge valve, the diver tilts his head so that the accumulated water covers the valve, presses the mask against the face and then exhales firmly and steadily through the nose. The increased pressure in the mask will force the water through the valve. Occasionally, more than one exhalation will be required.

7-7.3 Hose and Mouthpiece Clearing. The mouthpiece and the breathing hoses can become flooded if the mouthpiece is accidentally pulled from the mouth. With a

Figure 7-9. Clearing a Face Mask. To clear a flooded face mask, push gently on the upper or side portion of the mask and exhale through the nose into the mask. As water is forced out, tilt the head backward or sideway until the mask is clear.

single-hose scuba this is not a serious problem since the hose (carrying air at medium pressure) will not flood and the mouthpiece can be cleared quickly by depressing the purge button as the mouthpiece is being replaced.

To clear a double-hose scuba regulator that has flooded, the diver, swimming in a horizontal position, should grasp the mouthpiece. The diver should then blow into the mouthpiece, forcing any water trapped in it out through the regulator's exhaust ports. The diver should carefully take a shallow breath. If water is still trapped in the mouthpiece, the diver should blow through it once more and resume normal breathing. If the diver is out of breath, he should roll over onto his back and the regulator will free flow.

7-7.4 Swimming Technique. In underwater swimming, all propulsion comes from the action of the legs. The hands are used for maneuvering. The leg kick should be through a large, easy arc with main thrust coming from the hips. The knees and ankles should be relaxed. The rhythm of the kick should be maintained at a level that will not tire the legs unduly or bring on muscle cramps.

7-7.5 Diver Communications. Some common methods of diver communications are:

through-water communication systems, hand signals, slate boards, and line-pull signals. Communication between the surface and a diver can be best accomplished with through-water voice communications. However, when through-water communications are not available, hand signals or line-pull signals can be used.

7-7.5.1 Through-Water Communication Systems. Presently, several types of through-water communication systems are available for scuba diving operations. Acoustic systems provide one-way, topside-to-diver communications. The multidirectional audio signal is emitted through the water by a submerged transducer. Divers can hear the audio signal without signal receiving equipment. Amplitude Modulated (AM) and Single Sideband (SSB) systems provide round-robin, diver-to-diver, diver-to-topside, and topside-to-diver communications. Both the AM and SSB systems require transmitting and receiving equipment worn by the divers. AM systems provide a stronger signal and better intelligibility, but are restricted to line-of-sight use. SSB systems provide superior performance in and around obstacles. Before any through-water communication system is used, consult the NAVSEA/00C Authorized for Navy Use (ANU) list.

7-7.5.2 Hand and Line-Pull Signals. Navy divers shall only use hand signals that have been approved for Navy diving use. Figure 7-10a and Figure 7-10b present the U.S. Navy approved hand signals. Under certain conditions, special signals applicable to a specific mission may be devised and approved by the Diving Supervisor. If visibility is poor, the dive partners may be forced to communicate with line-pull signals on a buddy line. Line-pull signals are discussed in Table 8-2. Hand signals and line-pull signals should be delivered in a forceful, exaggerated manner so that there is no ambiguity and no doubt that a signal is being given. Every signal must be acknowledged.

7-7.6 Buddy Diver Responsibilities. The greatest single safety practice in Navy scuba operations is the use of the buddy system. Dive partners operating in pairs are responsible for both the assigned task and each other's safety. The basic rules for buddy diving are:

Always maintain contact with the dive partner. In good visibility, keep the partner in sight. In poor visibility, use a buddy line.

■ Know the meaning of all hand and line-pull signals.

If a signal is given, it must be acknowledged immediately. Failure of a dive partner to respond to a signal must be considered an emergency.

Monitor the actions and apparent condition of the dive partner. Know the symptoms of diving ailments. If at any time the dive partner appears to be in distress or is acting in an abnormal manner, determine the cause immediately and take appropriate action.

Never leave a partner unless the partner has become trapped or entangled and cannot be freed without additional assistance. If surface assistance must be sought, mark the location of the distressed diver with a line and float or other locating device. Do not leave a partner if voice communications or line-pull signals are being used; contact the surface and await assistance or instructions.

Establish a lost-diver plan for any dive. If partner contact is broken, follow the plan.

STOP

Clenched fist.

SOMETHING IS WRONG

Hand flat, fingers together, palm out, thumb down then hand rocking back and forth on axis of forearm.

This is the opposite of Okay. The signal does not indicate an emergency.

I AM OKAY or ARE YOU OKAY?

Thumb and forefinger making a circle with three remaining fingers extended (if possible).

Divers wearing mittens may not be able to extend three remaining fingers distinctly. Short range use.

OKAY ON THE SURFACE (CLOSE)

Right hand raised overhead giving Okay signal with fingers.

OKAY ON THE SURFACE (DISTANT)

Both hands touching overhead with both arms bent at 45° angle.

Given when diver is close to pickup boat.

Given when diver is at a distance from the pickup boat.

DISTRESS or HELP or PICK ME UP

Hand waving overhead (diver may also thrash hand in water).

Indicates immediate aid is required.

WHAT TIME? or WHAT DEPTH?

Diver points to either watch or depth gauge.

When indicating time, this signal is commonly used for bottom time remaining.

GO DOWN or GOING DOWN

Two fingers up, two fingers and thumb against palm.

GO UP or GOING UP

Four fingers pointing up, thumb against palm.

Hand slashing or chopping at throat.

I NEED TO BUDDY BREATHE

Fingers pointing to mouth or regulator.

Hand slashing or chopping at throat.

I NEED TO BUDDY BREATHE

Fingers pointing to mouth or regulator.

Indicates signaler is out of air.

Signaler's regulator may be in or out of mouth.

Figure 7-10a. Scuba Hand Signals.

COME HERE

Hand to chest, repeated.

ME or WATCH ME

Finger to chest, repeated.

OVER, UNDER, or AROUND

Fingers together and arm moving in and over, under, or around movement.

Diver signals intention to move over, under, or around an object.

LEVEL OFF or HOW DEEP?

Fingers and thumb spread out and hand moving back and forth in a level position.

GO THAT WAY

Fist clenched with thumb pointing up, down, right, or left.

Indicates which direction to swim.

WHICH DIRECTION?

Fingers clenched, thumb and hand rotating right and left.

EAR TROUBLE

Diver pointing to either ear.

Divers should ascend a few feet. If problem continues, both divers must surface.

I'M COLD

Both arms crossed over chest.

TAKE IT EASY OR SLOW DOWN

Hand extended, palm down, in short up-and-down motion.

YOU LEAD, I'LL FOLLOW

Index fingers extended, one hand forward of the other.

Figure 7-10a. Scuba Hand Signals.

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