Lang, M.A. and R.D. Vann (eds.). 1991. Proceedings of the AAUS Repetitive Diving Workshop. Duke University, NC. 339 p.

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Although diving is a relatively safe activity, all persons who dive must be aware that there is an inherent risk to this activity. Currently, the risk of decompression illness in the United States is estimated at 1-2 incidents per 1,000-2,000 dives for the commercial diving sector, 2 incidents per 10,000 dives for recreational diving activities and 1 incident in 100,000 dives for the scientific diving community.

Recreational Diving
Peter B. Bennett, Moderator

1. Scientific diving programs provide continuous training, recertification and dive site supervision, which helps maintain established safe diving protocols. Recreational divers, who may lack such direct supervision, need to be aware of their need to stay within established protocols, especially when making repetitive dives over multiple days, in which the risk of DCS may be higher.
2. It is recommended that attention of divers be directed with emphasis on the ancillary factors to decompression risk such as fitness to dive, adequate rest, hydration, body weight, age and especially rate of ascent which should not be more than 60 feet per minute.
3. Divers are encouraged to learn and remember the signs and symptoms of decompression illness and report them promptly so as to receive effective treatment as rapidly as possible to prevent residual injury.
4. The use of oxygen breathing on the surface, whenever possible via a demand regulator mask system, to insure the highest percentage of oxygen to the patient, is recommended while awaiting treatment if decompression illness is thought to be present. The use of 100% oxygen in the water while awaiting treatment is not recommended for recreational diving.
5. There is a strong need for more controlled data on the relationship of decompression illness to multi-level, multi-day diving, especially with the provision of baseline data. Such a study could be made from information gathered from closed groups such as certain island areas and liveaboard fleets where heavy recreational diving activities occur.
6. To help obtain information, dive computer manufacturers are encouraged to provide data loggers to computers so that a permanent record is available of dive depth, dive time, rate of ascent, etc. as close as every minute. This should be coupled with detailed accident reporting forms (e.g. DAN form) in the case of an accident.

Scientific Diving
Glen H. Egstrom, Moderator

1. The position of recommending slower ascent rates seems to have gained support.
2. Increasing knowledge regarding the incidence of DCS indicates that our ability to predict the onset of DCS on multi-level, multi-day diving is even less sensitive than than our ability to predict DCS on single square dives.
3. Although there is little evidence supporting either a pro or con position on multi-level, multi-day dives and a higher probability of DCS, there is sufficient evidence to encourage additional research on the problem.
4. There appears to be good evidence that there are many variables which can affect the probability of the occurrence of DCS symptoms. The ability to mitigate these variables through education, good supervision and training appears to be possible in such variables as hydration, fitness, rate of ascent, fatigue et al. and should continue to be promoted. Divers are subject to a host of specific conditions which may increase risk if precautions are not taken.
5. There appears to be support for the use of enriched air nitrox and surface oxygen breathing in scientific diving where higher gas loadings are anticipated in multi-level, multi-day dives. Adequate technical support is fundamental.
   6. Since there seems to be little likelihood that we can avoid all decompression illness in multi-level, multi-day diving, we should focus educational objectives on:

a. the development of an appreciation for the realities of risk for DCS;
b. encouraging maximal prevention strategies; and
c. define, as clearly as possible, the conditions under which problems are known to occur.

6. There are techniques used in commercial diving applications which may be appropriate for some scientific diving applications which require unusual exposures.
7. The incidence of DCS in scientific diving appears to be about 1:100,000, in recreational diving at about 2:10,000 and in commercial diving at about 1:1,000-2,000. These levels are not unreasonable.

Commercial Diving
Gary L. Beyerstein, Moderator

The following comments represent a consensus of the ADC members represented at this workshop.

1. Repetitive diving, multi-level and multi-day diving modes are considered normal, routine and essential practices in the commercial diving industry. They are performed safely and efficiently.
2. The use of surface decompression using oxygen is also essential to the safe and efficient conduct of commercial diving operations. Alternate methods to date have shown increased risk to the diver and have not reduced the incidence of DCS.
3. The quality of decompression (i.e. the effectiveness of the decompression table in controlling decompression stress) is much more important than the mode used when considering DCS risk.
4. A zero bends incidence rate is desirable but not thought to be achievable in all types of commercial diving. Given the commercial situation, with the ability to treat immediately and effectively, an incidence rate of 1 type I case of DCS per 1,000 to 2,000 dives is considered currently tolerable.
5. Current commercial practices and tables were developed from need and have been modified for safety. We feel they are currently tolerable. We look forward to a new generation of safer tables that will also increase our operational efficiency. Such tables will have longer bottom times at deeper depths without higher levels of risk. Such tables will need field validation. This will be greatly assisted by advanced dive profilers, field Doppler units, and an industry data base. We look forward to industry standard tables and therapy procedures.

Dive Computers
John E. Lewis, Moderator

1. No data were presented that warrant revision of the recommendations of the 1988 AAUS Dive Computer Workshop.
2. Data presented indicate that limiting dives to the no-stop (No-D) range, plus training and experience adds up to a one hundred fold decrease in the incidence of DCS.
3. Multi-level diving is a commonly accepted practice, and it appears to be less stressful than square wave profile diving.
4. Repetitive NoD (no-stop) diving with dive computers within the tested envelope is a valid practice. Deep repetitive dives with short surface intervals should be given special consideration.
5. No data were presented that indicate multi-day diving requires any special rules.
6. To assist in the analysis of decompression illness, dive computer manufacturers should consider working with the Divers Alert Network to provide an indication of inert gas loading by profile recovery, group letter, or other simple technique.
   

1. Because of limited analysis of the existing profile database, no conclusions have been reached regarding repetitive diving limits.
2. Paper databases are too cumbersome, it is considered essential that future profile recorders have the ability to download dive profile information directly to personal computer (through standard I/O ports).
3. The following desirable dive recorder features were identified:

a. ascent/descent rate record;
b. long storage capacity (commercial diver suggested one month);
c. for data points collected in large time intervals (i.e. 2.5-3 minutes), the average depth during the interval as well as the maximum depth attained during the interval should be recorded;
d. depth resolution should be at least .3 msw (1 fsw);
e. "low" tech recorder (inexpensive, requiring daily dumps);
f. date/time stamps on each dive; and
g. diver/recorder identification.

4. Possible dive recorder enhancements:

a. two-way communication with personal computer (i.e. allows adjustment in sampling rate, initialization of program variables, setting of recorders' internal clock, etc.); and
b. data compression techniques (i.e. store rate of depth change instead of depth) for both the recorder and final computer storage.

5. A standardization of information and file formats would be advantageous, with PENNDEC or CANDID databases as possible starting points.
   6. There is a need to obtain a list, from end users, of the minimal "header" information required. Suggested were:

   a. DAN incident form information; and
   b. time of incident to time of resolution.

Physiology, Medicine and Environment
Richard D. Vann, Moderator

1. Investigate the arterialization of gas emboli (VGE) as a potential mechanism for spinal and cerebral DCS.
2. Investigate the ability of reduced ascent rate and short decompression stops to reduce the incidence of VGE.
3. Dose-response curves for direct decompression are of fundamental importance to the development of decompression procedures.
4. Classification of decompression illness should be by specific signs/symptoms to guide therapy and prognosis and provide improved data for analysis.
5. There is a potential risk of bone necrosis for long shallow dives followed by inadequate decompression.
6. Multiple decompressions per day for multiple days can be potentially hazardous. The number of dives per day and the number of consecutive days during which diving can be conducted with reasonable safety is uncertain at present and depends upon the decompression procedures that are used.

Data Analysis and Procedure Calculation
R.W. Hamilton, Moderator

1. Maximum likelihood and other statistical techniques are useful for evaluation and assessment of new procedures based on past experience.
2. Predictive models are sensitive to the data set used to determine the parameter estimates of the model.
3. Field data can be useful and data exchange should be encouraged.

Decompression Trials
Ronald Y. Nishi, Moderator

1. After all these years, we still do not know much about DCS. None of the table or dive computer developers really have decompression "models". What they actually have are decompression calculation methods as stated by Brian Hills in his book "Decompression Sickness".
2. There are two primary methods for developing decompression tables and designing decompression trials. The first is the traditional approach, where tables are developed from some model and selected profiles are dived to test whether or not DCS occurs. A variation on this approach is to include risk analysis. Dives are tested, either by following printed tables or by following dive computers. It is necessary to use other tools such as Doppler and complement analysis to determine decompression stress.
3. The second approach to designing trials is the probabilistic method. In this case, a large amount of carefully documented (well-calibrated) dive data is required to estimate the risk of DCS, compute optimum profiles and test with appropriate criteria for rejecting or accepting profiles. With the proper design of sequential tests, the total decompression time can be minimized and the number of trials and cases of DCS can also be minimized. The probabilistic method appears to be the way of the future but still needs further development. To make it work, accurate dive data and DCS information are required, which the military, scientific, commercial and recreational diving communities must supply.
4. What does this all mean for the scientific, recreational and commercial diving communities? Although designers and testers of decompression trials may talk about incidences or risks of DCS which are much higher than the different communities are willing to accept, the eventual tables will probably be more effective than those commonly in use now. It must be kept in mind that DCS is a probabilistic event.
   

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