As interest in the oceans and the capability to work there increases, it is becoming more apparent that facilities must be provided to the scientific and working diver to enable him to remain at depth for long periods of time. In 1958, Captain George Bond, U.S.N., conducted laboratory experiments that led the way to the development of saturation diving (Bond 1964). Saturation refers to the state of dissolved gases in the tissues of a diver. Under a saturated condition, the tissues have absorbed all the nitrogen or other inert gases possible at the saturation pressure. Once this has occurred, the decompression time required at the end of the dive of a given depth does not increase with additional time spent at that depth. Under such conditions, the diver works out of a pressure facility in which the atmosphere is maintained at approximately the same pressure as that of the water in which he is working. His "habitat" may be an ocean floor installation, or it may be a pressurized chamber on board a surface vessel from which he travels to his work location in a pressurized personnel transfer capsule (PTC). In either case, he does not undergo decompression between dives; he is decompressed only after the total dive sequence is completed.

This method of diving is essential for the scientist who needs to spend long periods on the bottom and for the working diver who cannot afford the costbenefit ratio of short dives and frequent long decompressions. Since 1958, saturation diving programs have been conducted in over 15 nations, both in land-based hyperbaric chambers and in the open sea. The depths of such programs have ranged from 35 to 2,000 feet.

While the U.S.Navy and the commercial diving industry are devoting significant efforts to develop deep saturation diving technology in the 500- to 2000-foot range, the scientific community is con

centrating on the use of saturation diving in shallower waters (50 to 300 feet).

This section discusses various aspects of saturation diving and provides tables for excursion diving, decompression, repetitive dives, and aborted dives from saturated conditions in the 50- to 250-foot range.

12.1 GENERAL PRINCIPLES OF SATURATION DIVING

The tissues of a diver's body absorb inert gases as a function of the partial pressure of the breathing medium, the duration of the dive, the type of breathing gas mixture being used, the characteristics of the individual diver's tissue, and his condition at the time of the dive. In dives of long duration, the body tissue becomes saturated with dissolved inert gas at the partial pressure of the breathing medium in approximately 24 hours. The techniques of saturation diving make use of the fact that once the body reaches this equilibrium, it can safely remain saturated for long periods of time (Pauli and Cole 1970). Two basic approaches are commonly used in saturation diving. They are:

1. Habitat/Ocean Floor Laboratory. A habitat is a pressure or ambient vessel, placed on the floor of the ocean, which provides support, comfort, and a base of operation for the saturated diver and his equipment. Habitats usually are maintained at ambient pressure. Water is prevented from entering the habitat by the gas pressure inside. This permits divers to enter and exit the habitat usually by means of an opening in the habitat floor.

2. Deep Dive Saturation System. A deep dive saturation system consists of a deck decompression chamber (DDC) located on a surface support platform, and a pressurized personnel transfer capsule (PTC) in which the saturation diver commutes to

and from his work site. The DDC, which provides facilities for the comfort of the saturated diver, is maintained at the pressure of the work site depth. The PTC (which can be a diving bell or a lock-out submersible) is also maintained at working depth pressure. The PTC is mated to the DDC to enable the diver to remain at working pressure at all times during transfer operations.

12.2 OPERATIONAL FACTORS

The saturation diver working from a habitat or PTC has direct access to his work. As mentioned earlier, the bottom time or time at the work site is greatly extended because compression and decompression procedures are not required with each excursion into the water. A significant psychological advantage also accrues to divers with the reassurance and convenience of a dry chamber from which to make excursions or to which they may return quickly in case of fatigue or other difficulty.

12.2.1 Breathing Equipment and Mixture

The saturated diver may use a variety of underwater breathing apparatus. Open-circuit scuba, closed-circuit scuba, or umbilical-supplied breathing apparatus (hookah) all are suitable for use from either a habitat or a deep dive saturation system. These systems are described in detail in Section 4. The majority of these systems are designed to support diving operations at depths compatible with a habitat or deep dive system.

The breathing medium used in the habitat or deep dive system is dependent on the depth of the work site. Relatively shallow systems (0 to 100 feet) use compressed air or nitrogen-oxygen breathing media, while deep systems currently are using helium-oxygen mixtures. Experiments are being conducted that should result in other gases being used in the future such as argon, neon, and hydrogen.

12.2.2 General Procedures

A diver experiencing saturation for the first time on the seafloor has much to learn. Although the general procedures and equipment are the same as when diving from the surface, there are some important differences. The diver must:

Become familiar with the habitat, its operation, and all emergency procedures (See Paragraph

12.4 and Section 14).

Return to a pressurized or ambient chamber rather than the surface following a dive.

■ Orient geographically to avoid getting lost, using lines or transects laid out from the habitat.

Provide himself with redundant regulators and tanks.

■ Wear a compass at all times.

Always wear a depth gauge and know the vertical excursion limits (See Paragraph 12.5).

Not wear a flotation device that could accidentally inflate and carry him to the surface. ■Not wear a quick-release weight belt. ■ Take particular care with equipment when compressing to depth and making excursions. Items such as cameras, sealed containers, etc.. may implode or explode because they often are not designed to withstand both excess internal and external pressures.

Missions must be planned to account for time. distance from the habitat, number of divers, breathing gas (composition and quantity), vertical excursions, life of carbon dioxide absorbent in closed-circuit breathing systems, and any special diver heating or communication equipment that may be required.

12.3 LIFE-SUPPORT FACTORS

Each habitat has its own characteristics that must be learned by a diver (See Section 14). Training programs usually are given, which provide the necessary information. There are a few things, however, that are directly related to the saturated condition of a diver in all habitats.

For most habitats and personnel transfer capsules. the partial pressure of oxygen should be maintained at between 0.19 to 0.5 atmospheres. The carbon dioxide partial pressure should be between 2 to 7 millimeters of mercury. Carbon monoxide, as a trace contaminant, must not exceed a partial pressure of 15 × 10-3 millimeters of mercury.

Buildups of carbon dioxide in habitats and PTCare prevented by the use of a carbon dioxide scrubbing system or by venting. The heart of a scrubbing system is a chemical, usually barium hydroxide. soda lime, or lithium hydroxide, which absorbs the carbon dioxide. The length of time this absorber will remain active prior to becoming saturated wit CO2 is directly related to the CO2 output of th

divers and the ambient temperature. The storage and replacement of canisters is a simple process. The number of canisters required depends on the length of the mission. The man-hour rating of a particular absorbent is provided by the manufacturer. It is known, however, that the efficiency of some CO2 absorbents decreases drastically at lower temperatures.

Table 12-1 summarizes the characteristics of barium hydroxide, lithium hydroxide, and soda lime. Barium hydroxide is used in underwater breathing apparatus, hyperbaric chambers, ocean floor laboratories, and submersibles. Soda lime, a lower cost material, is not used in underwater breathing apparatus because it forms a highly caustic solution with water; however, it appears acceptable for use in scrubbers for other closed systems. Lithium hydroxide is the lightest of the absorbents, but requires the same canister volume as the others and is much more expensive. It also forms a caustic solution with water.

The rate at which carbon dioxide is absorbed is influenced by temperature, and is considerably lower at 40° F than at 70° F. In some scrubbers sized for adequate performance at 70° F, absorbing capacity at 40° F may be as little as 1/3 that at 70° F. This effect is strongly dependent upon the canister design and the rate of carbon dioxide absorption, being most evident in absorbers working at peak flow rates, and least evident in oversized scrubbers and those used intermittently.

It appears highly desirable to provide external insulation and heating of scrubbers for use in cold water as a means of minimizing size and assuring that the design absorbent capacity can be obtained. This is also advisable as a means of avoiding mois

ture condensation. A possible alternative is to design for about three times the absorbent capacity needed at 70° F.

The efficiency of absorbents is also influenced by relative humidity. The absorbing capacity quoted for barium hydroxide and soda lime absorbents is obtained only when relative humidity is above 70 percent. Lower humidity levels result in less absorbent capacity. Breathing-gas humidity will normally be well above 70 percent unless the scrubber is preceded by a dehumidifier.

Under conditions of high gas humidity and low scrubber surface temperature, it is possible to condense water on the canister walls or in the absorbent. This is undesirable because wet absorbent is inactive and impervious to air flow, reducing absorptive capacity and increasing pressure drop through the canister.

Divers must remain alert for early symptoms of carbon dioxide poisoning (See Figure 11-2). An auxiliary scrubbing system frequently is used as a backup in case of primary system failure. If a backup scrubber system is not available, the chamber (habitat) should be ventilated at a rate of 2 cubic feet per minute (chamber volume) of breathing gas for each diver at rest, and 4 cubic feet per minute for each diver not at rest (Lanphier 1957). Comfortable temperature and humidity ranges have been found to be 78° to 83° F and 50 to 75 percent. respectively, in air or nitrogen/oxygen environments at shallow depths. At deeper depths, or when saturated in a helium/oxygen atmosphere, a temperature as high as 92° F may be required to maintain a comfortable environment.

12.4 EMERGENCY PROCEDURES

A well-conceived operation must include a contingency plan that charts a course of action should a primary life-support system fail or other emergency arise. Any contingency plan should consider diver safety as first priority. Emergency conditions in a habitat or personnel transfer capsule, however minor, pose threats to diver safety that are not found in nonsaturated diving. If a situation arises which makes the habitat uninhabitable, an alternate place must be available where divers can go and undergo decompression safely.

The following emergency procedures are general in nature and are intended to be applicable to all habitats and personnel transfer capsules. Since, however, most habitats and PTC's are "one of a kind" systems, certain differences in hardware and design will dictate specific procedures that should be followed for each.

WARNING

Complete Emergency Procedures Must Be Developed for Each System, and All Surface Support Personnel as Well as Divers Must Become Familiar With Them.

12.4.1 Fire

Fire is probably the most critical emergency that can threaten a saturation system. Shallow water habitats using air as a breathing medium are more susceptible to fire, because air becomes more combustible under pressure than gas mixtures with a lower oxygen content. It has been shown that burning rates under hyperbaric conditions are primarily a function of the percentage of oxygen present (Schmidt et al. 1973).

In shallow habitats using nitrogen-oxygen as a breathing medium, fire is less of a danger because oxygen is partially replaced by nitrogen. At greater depths, where helium is used with low percentages of oxygen, fire is even less of a threat. Care must be taken, however, when oxygen is used during decompression.

WARNING

Overload Dump Systems for Decompression Are in Order to Eliminate Exhaled Air From the e and Prevent the Buildup of Cr nike Habitat.

In the event of fire, the general procedures below should be followed:

1. Shut off all power to the chamber.

2. Put on emergency breathing masks and eye protection masks. Some habitats have masks for both oxygen and the chamber's saturation breathing medium; use the mask with the breathing medium.

3. Notify the surface immediately, using the primary communication system, an emergency/ backup system, or, when available, a diver underwater communication system.

4. Attempt to extinguish the fire using water.

5. Attempt to remove all flammable materials from the immediate area of the flames. Attempt. also, to discard smouldering material from the chamber.

6. Personnel not directly involved in fighting the fire should don diving gear and leave the chamber.

7. If the fire becomes out of control, abandon the chamber notifying the surface of this action if conditions permit. Proceed to available underwater bottom stations and await surface support.

12.4.2 Loss of Power

Most shallow water habitat systems have a primary power source and an emergency or standby power source. Primary power is usually 110 volts a.c.; emergency is 12 volts d.c. In some systems the emergency power is designed to activate automatically upon failure of the primary source.

Should primary power fail, perform the following procedures:

1. Activate the emergency power source if this system was not activated automatically by primarysource failure.

2. Notify surface support personnel and stand by to assist in isolating and remedying the cause of the failure.

12.4.3 Loss of Communications

Most saturation systems will have a backup system of communication. Sound-powered phones that require no external power often are used. In some cases, communications may be possible over diver communication circuits. When a communications failure occurs, communications should be immediately established on a secondary system, the surface notified of the primary system failure. and attempts made to reactivate the primary system.

12.4.4 Blow-Up

Inadvertent surfacing, commonly called a "blow-up," is a serious hazard facing a saturated diver, especially when he is using self-contained equipment and is not physically "attached" to a habitat or PTC by an umbilical or tether. Extreme caution must be exercised by a saturated diver while away from a habitat to avoid any circumstance that would require making an emergency ascent to the surface or a situation that might result in an accidental surfacing.

If a diver should surface, however, the following action must be taken:

1. Return the diver to the habitat or PTC immediately; or, if a recompression chamber is immediately available at the site, recompress the diver to his saturated depth.

2. If brought back down to a habitat or PTC, notify surface support personnel immediately.

3. Have the diver begin breathing pure oxygen immediately at depths no greater than 60 feet (U.S. Navy Diving Manual 1973).

4. Surface support personnel will determine whether the diver must undergo emergency recompression.

12.4.5 Lost Diver

A saturated diver performing work away from a habitat or PTC should be continually aware that he is dependent on that facility for life support. Any excursion should be carefully planned so that the way back is known and assured. As in all diving, buddy divers are a necessity. In a saturated condition, it is especially necessary for diving buddies to stay close together and to continually be aware of their location, significant landmarks, and the distance and direction back to the habitat or PTC. Many habitats, particularly those permanently fixed and continually used, have transect lines extending to various underwater areas. Divers should become familiar with these transect patterns and use them as reference points during excursions. Should a diver become lost, the following actions. should be taken:

1. Begin signaling by banging on a scuba cylinder with a knife, rock, or other hard object.

2. To conserve breathing gas, ascend to a depth where the bottom can still be seen clearly but which is not above the maximum upward excursion depth (See Table 12-3).

3. Begin making slow circular search patterns looking for familiar landmarks or transect lines.

4. Should a diver become "hopelessly" lost at saturation depths not exceeding 100 feet he should, while still having ample air, ascend slowly to the surface. Upon reaching the surface, take a quick (less than 30 seconds) compass sighting on the support system or buoy over the habitat and return to the bottom. He then should proceed directly toward the habitat after rejoining his buddy. It is critical that this action occur while ample air still remains.

12.4.6 Night Diving

Night excursions from a habitat are not uncommon, particularly for the scientific observation of marine life. Particular care must be taken to ensure that divers do not become lost during these excursions. Each diver must be equipped with two diver's lights, well maintained in good working condition, and equipped with fresh batteries. It is recommended, also, that each diver be equipped with an emergency light, preferably a flashing strobe, should a primary light fail or the diver becomes separated from his buddy. In emergencies, the strobe can be used for navigation if the diver shields his eyes from the flash. Also recommended is a flashing strobe on the habitat or PTC to assist divers in return should their lights fail.

12.5 EXCURSION DIVING FROM A SATURATION SYSTEM

Excursion diving from saturation in a habitat or DDC/PTC system requires special preparations and strict adherence to excursion diving tables.

A saturated diver may be compared to a diver at the surface who is saturated at 1 atmosphere, whereas the habitat diver is saturated in multiples of 1 atmosphere. The surface diver can make dives (excursions) to depth and return directly to the surface without decompression as long as he has not absorbed more gas during the excursion than his body can safely release. Similarly, habitat divers can make excursions either to greater depths (downward) or lesser depths (upward) by following the depth/time limitations of the excursion tables.

General rules cannot easily be given. Many factors change the conditions, such as cold, workloads, equipment used, experience, etc., and all such factors must be considered in any excursion or decompression. The following recommendations