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Supplemental Heating System for Self-Contained Divers

NOTE: I don't usually publish articles like this, but due to the revolutionary ideas contained in this article I thought many of you might be interested in reading it!


For nearly four decades self-contained divers have been seeking an effective, simple supplemental diving suit heating system. Major technological advancement in the 1970's offered several solutions; however, economic restraints, system complexity, and reliability factors deterred further development and production. The recent increase in cold weather diving activity has inspired the National Underwater Technology Laboratory researchers to re-evaluate the potential solutions to self-contained supplemental diver suit heating.


The self-contained supplemental diver suit heating system must be simple to develop, fundamentally maintenance free, economically feasible for any recreational diver to own, and functional over a range of environmental conditions. Ideally, the system should be independent of electrical power sources, require no externally mounted heating/control unit, be readily adaptable to any diving suit commonly used by self-contained divers, easily transportable, unisexual, and marketable through numerous retail business outlets. Naturally, the economic restraints can involve some compromises in system design and function. Preliminary literature research, field testing of existing units (both production and prototype models), and interviews with 4,286 recreational divers, 477 commercial divers, 88 military divers, and 675 parents/spouses of active divers resulted in the rejection of all currently available heating systems, systems presently controlled by patents, and systems currently under federally funded design contracts with the exception of one. This single, potentially acceptable system proved to be the "first" supplemental diver suit heating system ever documented in the world. However, further research revealed that the system had never achieved wide public acceptance because of misunderstood concepts, social stigma, marginal control mechanism, and poor marketing practices. Further government sponsored research would provide solutions to these problems.


The most acceptable supplemental diver suit heating system known to mankind today is the heated fluid system. Umbilical supplied divers have used this system for more than two decades with hot water being supplied from a surface or diving bell water heater. The delivery tube is insulated to prevent substantial heat loss between the source and the diver. Delivery tube heat loss has been a problem generally resolved by elevating the temperature of the water at the source. The introduction of this system into umbilical supplied commercial diving drew praise and endorsement from all facets of the diving community. Diver acceptance was immediate and overwhelming. It stands to reason that an equivalent system should, in fact, be feasible for the scuba diver. The first problem considered was the diver's suit. Evaluation of 17 commercially available foamed neoprene wet-type diving suits and 32 dry-type diving suit/underwear combinations revealed that any presently available scuba diver's suit could be adapted to accept a self-contained hot fluid heater.

The delivery tube was considered next. Examination and evaluation of 316 potential delivery tubes suggested that tube configuration would not be a problem and that the length could be as short as 2.5 cm. Both visual and digital methods were used in tube evaluation. Tubes were readily available and no special provisions would be required in system design. Although some tubes were found to be more adequate than others, all proved to be functional and acceptable. Both internal and external configurations were found interesting and acceptable.

Fundamental to the system is the heating component. Design criteria dictates that the system can contain no electrical components that might result in electrical shock to the diver.

The heater must also be located within the suit itself and operational without manual/digital manipulation. The system must also be capable of supplying a reasonable, but limited, supply of hot water at a temperature of about 37 degrees C. Since normal body temperature for human beings is 37 degrees C., it was deemed feasible to use the human body itself as the heating source. In laboratory experiments, measurements of temperature of water heated by the human bodies of 697 experimental subjects (male and female, age range 4 to 67 years, weight range 52 to 293 lbs) revealed that all water temperatures fell with in an acceptable range of + .5 degrees C.

The next problem was identification of an acceptable, compact, readily available, insulated fluid container which could be easily carried by a self-contained diver inside of the diving suit. Although the solution to this problem was obvious to some members of the research team, a comprehensive study of nearly 180 insulated containment vessels was undertaken in order to objectively identify the most acceptable vessel. The flexible containment vessel selected for this system was the human bladder which is insulated from external environment cooling by natural body insulation, comes equipped with a fluid delivery tube, and is directly heated by the body heat source with no special adaptation. The human bladder is extremely attractive from an economic point of view since every potential diver is so equipped. This eliminated a need for research and development cost, testing, UL approval, OSHA regulation (for use in a commercial diving mode), market survey, and so on. Fluid source and chemical composition is probably the single most important factor in the development of the system. Since the design criteria specifies that there can be no manual or digital control mechanism, both fluid retention and release must involve natural body capabilities and capacities. The quantity of fluid that can be retained by an individual bladder is quite variable within the human diver population. An experimental population of 187 human subjects was selected from more than 2,600 applicants for the fluid capacity and retention experiments. This subject population included both males and females ranging in age from 12 to 72 years of age. Body fat composition ranged from 9.8 to 52.6%. Complete anatomical measurements were recorded for each subject along with a comprehensive physiological and psychological profile.

The subjects were required to drink variable amounts of different fluids in order to obtain quantitative data on capacity, retention time, and release profiles. Two hundred sixty-six different fluids known to be consumed by humans were tested in this experiment. These fluids included distilled water, Southern Comfort (both 80 and 100 proof), treated Huron River water designated acceptable for human consumption in Ypsilanti, Michigan, Columbian Dark special brew coffee, Hi-C fruit punch, Pepsi Cola, and goat's milk. Alcohol-containing fluids were eliminated from the study because of the possible adverse effects on the divers. However, there are reports of at least one Detroit area dive shop and a Harper Woods area high school woman's softball team who are continuing the alcoholic fluids experimentation independent of this research project. The most satisfactory fluid was found to be "coffee" obtained from a truck stop at the intersection of Dexter Road and I-94 near Ann Arbor.

Once the primary fluid was identified, studies of capacity and retention could begin. The variables included: (1) the amount of coffee that an individual could consume within a specified time period prior to diving, (2) the length of time that elapsed between consumption and both voluntary and involuntary release of urine, (3) physical discomfort level in full scuba diving equipment (including weight belt) measured subjectively on a scale of 1 to 10, and (4) the number of hot fluid discharges during a 40 minute submergence in water temperatures ranging from 2 to 8 degrees C.

The amount of coffee that could be consumed within one hour prior to the dive ranged from .94 to 3.64 liters with a mean of 1.66 liters. The length of time between completion of consumption and involuntary urine release ranged from 1.27 minutes to 77.32 minutes for 67% of the test subjects who did, in fact, experience involuntary urination. The average male demonstrated a higher capacity and longer retention capability than the average female, although exceptions were noted. Seventeen percent of the test subjects experienced only one generous fluid release during the 40 minute test dive whereas 5% demonstrated the capability to voluntarily achieve 3 or more controlled releases of variable quantity during the dive.

Staggered coffee consumption at 20 minute intervals appeared to be significant in inducing more than one controlled release during the dive.

The research team concluded that 78% of the test population could consume enough coffee and experience sufficient hot urine discharge during the dive to achieve moderate to exciting warming effects of sufficient magnitude to comfortably increase their dive duration as compared to dive exposures involving no hot urine discharge.


Test subjects were required to evaluate the hot fluid heating system adapted to both dry- and wet-type diving suits. Wet-type suits were custom sized and lined with nylon fabric bonded to the foamed neoprene. Both thin fabric and foamed neoprene dry-type suits were tested. Underwear for dry suit divers included pile, Thinsulate, and wool garments of varying thicknesses.

Wet suit-fitted divers experienced more initial chilling at time of entry, and it was felt that this contributed to the shortening of time between entry and involuntary fluid release. Furthermore, most wet suited divers voluntarily initiated hot fluid warming procedures sooner than their dry suit-fitted counterparts. The mean time for fluid release warming for wet suit divers was 18.2 minutes after submergence whereas the dry suited divers delayed release until 27.8 minutes.

Divers fitted with standard design wet suits complained of more rapid cooling following the release of heating fluid and often desired a second fluid warming within 5 to 8 minutes of the initial warming. This is explainable on a basis of ambient water flushing of the suit. The heated fluid distribution within the diver's wet suit remains as a major variable dependent on the individual heater release pressure (or force) and diver talent in distributing the fluid through various body maneuvers. Heating of the groin, torso, and upper leg was considered acceptable by all subjects. Depending on the position of the discharge tube, male divers noted more variation in heat transfer (fluid distribution) from front to back with the front side of the torso generally favored in distribution. Female subjects generally experienced more even front and back distribution. Forty-seven percent of the divers claimed to succeed in distributing warmed fluid over 90% of the body surface including feet, hands, neck, and head. The amount and significance of the distribution remains as a subject for further research. The more successful distributions appeared to be complimented by various body positions and movements such as standing on the head, pumping motions of the arms and legs, and shimmy-like movements.

Wet suit designs which included waterproof seals at the wrist, fitted boots (attached), attached hood, and entry through a waterproof zippered opening were preferable to standard design wet suits. Ambient water flushing could be eliminated with sealed suits. More significantly, the heated fluid was retained in the suit from the time of release until the suit was removed following the dive. Furthermore, fluid distribution was much simpler and complete.

Dry suit divers remained generally warmer than wet suit divers from the time of submergence until fluid release warming was needed or involuntarily occurred. Fluid distribution was somewhat restricted to the upper leg and torso area because of fluid soaking and retention by the underwear. Wool retained the most fluid, followed by pile and Thinsulate, respectively. Vapor barrier Thinsulate underwear proved most satisfactory.

Post dive comfort and undressing was also studied. Wet suit-fitted divers expressed little or no feelings of discomfort following the dive while wearing the suit for the mandatory 15 minute surface interval. Cooling was noted and fluid drainage from the leg openings was noted on most divers; however, neither of these appeared to be significant. The sealed wet-type suit fitted (snug fitting with no underwear) divers noted fluid accumulation in the legs and boots with a sensation of sloshing when they walked about. Cooling was less than in standard wet suit designs, and several test subjects activated their fluid release system on land to demonstrate the feasibility of above-water heating. Exceptional above-water fluid distribution was achieved by standing on their hands for a few seconds.

Suit removal appears to be the only factor that will require considerable further study and accessory components. In order to more objectively evaluate the significance of suit removal, spouses, parents, children, family dogs, and significant others were placed in a 10 ft x 14 ft dressing room with their respective subject to witness and evaluate the undressing process. They were given a rating list on which they were to record impressions and recommendations using a 1 (excellent; no problem) to 10 (completely unsatisfactory; unbearable) rating system. The mean response to 100 evaluation factors was 8.02 for the entire response group with dry suited divers receiving a mean score of 9.76.

The research team observed the evaluation session through one-way mirrors. Forty-seven mothers lost consciousness within 28 seconds after the suit was first opened and 18 experienced crying/sobbing episodes. Eighty-six spouses/significant others were observed to reject any attempt at post dive expression of affection such as kissing or hugging. Twenty-three young children were noted to vomit within 4 minutes of the suit opening.

Family pets (dogs) exhibited the most interesting responses. Within 32 seconds of the suit opening, all dogs had demonstrated some response. Most immediately raised their heads and sniffed in the direction of their diver/master. Nine of ten then moved toward the diver with raised head and expression of increasing interest. Three Great Danes were observed to knock their master to the floor and repeatedly roll their bodies over that of their master. Family members finally restrained the dogs so that the divers could complete undressing. One Doberman immediately grabbed his diver's underwear, ran to a corner with it, and refused to surrender it to anyone including his master. The dog was eventually rendered unconscious with a tranquilizer dart in order to retrieve the underwear for analysis. Finally, one toy poodle ran to his diver and attempted to have a sexual experience with the diver's lower leg. Numerous other behavioral displays were noted. Only two divers were bitten by their family dogs. In one case, a wife was heard to say, "Attack, Fang, attack now!" The general conclusion of the research team was that dogs are more accepting of the hot fluid heating system than other family


It was also noted by the research team that plants in the dressing rooms started to wilt within 13 minutes of the suit opening and more delicate house plants died within 24 hours. The outdoor open water dive sites were revisited to assess the surrounding flora. Three species of shrubs and trees were found to be dead or severely damaged within 100 m of the undressing site. Many nearby trees exhibited premature leaf loss.


A successful supplemental heating system for self-contained divers is currently available to the general diving population at minimal cost per use. Every diver should be normally equipped with the basic components including a self-contained fluid heater, fluid storage container, delivery tube, and fluid processing system. Consequently, no additional cost for these components is anticipated. This fact, in itself, makes the system extremely attractive to the general diving population.

Considerable variation in fluid container capacity and fluid retention time was noted. Furthermore, these factors appeared variable from day to day within any individual test subject.

These variables do, to some degree, affect the efficiency of the system. However, all systems tested did function satisfactorily within allowable tolerances.

Fluid release control is also a variable. Preliminary results of this research suggest that, for the average diver, consumption of one-third of his/her coffee capacity at 50, 30, and 10 minutes preceding the submergence was more likely to result in two or more controlled releases of heated fluid during the dive. Further study will be required to determine a more precise formula for pre-dive filling of the containment vessel.

Although, all suits commonly used by scuba divers will accommodate the fluid heating system, the snug fitting wet-type suit with waterproof seals and zipper appears to be the most adaptable. Note that no underwear is worn with this suit. Although standard dry-type suits with various undergarments accommodated the system, fluid distribution was somewhat restricted.

Strong "truck stop" caffeinated coffee was most acceptable as an intake or charging fluid. Coffee from orange top pots appeared to be less satisfactory. Orange juice and goat's milk were less than acceptable.

Undressing appears to be the only problem to be resolved at the present time. A supplemental grant of $500,000 is being requested for 1991-92. Until further research is completed, the research team strongly recommends that divers undress only in the presence of other divers using the hot fluid suit heating system. Pets, friends, and family members should stay at least 100 m upwind. Also, the undressing procedures should not be undertaken within 100 m of endangered plant species. One researcher suggested that the diver open the neck seal slightly upon surfacing and administer 500 ml of eau de Cologne and wait 10 minutes before removing the suit.

A training program is currently being developed by the National Organization of Polar Diving Instructors. Preliminary information suggest that a comprehensive 23 hour program of theory, pool, and open water training will be necessary. This includes experimental sessions in fluid consumption to determine individual tolerances, relea