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© 2000 and 2001 Kirby Morgan Dive Systems, Inc., All rights reserved. Do not copy without written permission |
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KIRBY MORGAN DIVE SYSTEMS
Santa Barbara, California And Mike Ward |
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by
Pete Ryan, Bev Morgan, & Trent Schultz of KIRBY MORGAN DIVE SYSTEMS Santa Barbara, California And Mike Ward of The DIVE LAB Panama City Beach, Florida 11 March, 2000 |
| he results of tests at the Dive Lab in Panama City Beach, Florida, have shown that a problem has gone relatively unnoticed and unreported in open circuit SCUBA diving for many years. The refrigeration effect of gas pressure reduction in open circuit SCUBA is known, but has not been the subject of published information due to the lack of investigation on the subject. The refrigeration effect has been recognized as a factor in mechanical failure of the demand regulator when SCUBA diving in cold water, but the exact mechanical source and effect has not been defined. Most all divers have noticed that the air/gas coming from the open circuit demand regulators is cold, but just how cold? The physiological effects of the refrigeration of the breathing gas/air, (and the possible danger), to the open circuit sport SCUBA diver has not been investigated to our knowledge. In commercial deep diving using HeliOx gas mix using umbilicals, it is common practice to use hot water systems, not only to heat the exterior of the divers’ body, but also to heat the breathing gas. It is known that the breathing gas must be heated (in addition to heating the exterior of the body) for the divers’ core temperature to be maintained. Heating only the exterior of the diver’s body is not enough to keep the diver warm. Helium and Oxygen breathing mixtures (HeliOx) transfer heat about seven times more than air or Nitrogen/Oxygen mixtures (NitrOx). Divers using HeliOx on deep dives rapidly become cold by loss of body heat through respiration. The problem is overcome by heating the diver’s breathing gas (in addition to heating the exterior of the body). This is accomplished in most commercial diving operations with a flow of hot water through a shroud over the piping in which the diver’s breathing gas flows. The hot water is produced at the surface and sent to the diver through a hose that is part of the umbilical. SCUBA divers are not connected to the surface so they do not have this means of warming. Heating the sport SCUBA diver’s gas/air supply has not been done successfully. SCUBA diver heating efforts have focused on the exterior of the body by means of passive insulation and more recently, electrical heating with batteries. Since no obvious indicators point to cold inhalation gas/air being a problem to SCUBA divers it appears that no studies have been done to investigate this cold breathing gas/air effect on their physical well being. Mechanically, breathing regulators have been modified to retard freezing. While some designs do work to retard freezing, little success has been achieved in warming the gas/air temperatures to the diver. SCUBA divers store their supply of breathing gas/air in tanks that contain the compressed gas/air, Pressures of 3000 psi (206.8 Bar) are common in the United States, 4000 psi (275.8 Bar) in Europe and in some cases technical divers have used pressures of 6000 psi (413.7 Bar) or more. The use of higher-pressure storage tanks and mixed gas by deep divers has significantly increased the potential danger and risk associated with the breathing gas/air cooling effect of pressure reduction by the first stage regulator. A first stage regulator, usually attached to the tank valve, reduces the tank pressure to approximately 150 psi (10.3 Bar) This lower pressure is fed by means of a hose to a second stage demand regulator that is located near the divers’ mouth. The reduction in pressure by the first stage causes the compressed gas/air to greatly expand at the first stage flow orifice. The rapid expansion of gasses dramatically reduces the temperature of the breathing gas. The Dive Lab has found that drops of 50° F (27.8° C) are common and drops of 100° F (55.6°C) or more are possible when 6000 psi (413.7 Bar) storage pressures are used. The cooling appears to be linear and predictable. The higher the pressure at which gas is stored, the greater the temperature drop will be when the pressure is reduced to a typical low pressure of about 150 psi (10.3 Bar). When the diver is immersed in relatively warm water of 75°F (23.9 C) and is breathing from a tank of compressed air filled at 3000 psi, the low pressure air coming out of the first stage regulator is in the range of 25° F (or minus 3.9°C). That is below freezing. Most scuba divers do not sense this cold breathing gas and are not concerned. However, even at these warm water temperatures when using air or NitrOx, divers have been unknowingly using a great deal of body heat/energy to warm the cold gas inhalations. The lower temperature of the breathing gas shortens the time that it takes for the diver to get uncomfortably "cold" and start to shiver. In addition to diver heat loss through respiration, the cold inhalations are very dry causing increased dehydration to the diver. When the water temperature is 40° F (4.5° C) the temperature of the breathing gas is in the range of minus 10° F (minus 23.3° C) when the tank is full to about 3000 psi (206.8 Bar). When the water temperature is 32° F (0° C) the demand second stage regulator is being fed minus 18° F (minus 28° C) gas/air when the tank is full to about 3000 psi (206.8 Bar). On tests at these water temperatures our instruments showed these breathing air temperatures. Ice build up on the regulators being tested was impressive. We had one half inch coating of ice inside and outside of the demand second stage and the first stage was encased in a large, thick ball of ice. Needless to say the second stage mechanically failed in less than 5 minutes. A first stage equipped with a cold water environmental cap mechanically failed due to being entirely encased in ice. At these temperatures there is an immediate danger to the diver in two ways: First, ice may cause the regulator to mechanically freeze up threatening the diver’s supply of breathing gas. Second, the cold air hitting the diver’s mouth, throat, and airways presents a real danger of causing respiratory shock, which results in the diver not being able to breathe. We are not saying hard to breathe, but immediately and instantly can not breathe. The physical mechanism of respiratory shock is not fully understood by the authors. It appears that laryngospasm occurs. The diver’s airway is completely blocked by the epiglottis sealing the trachea closed. If the airway is blocked, embolism can occur even in relative shallow water if the diver goes toward the surface. Whatever the exact physical mechanism to the diver the result can be catastrophic. This may explain why some previous cold-water diving fatalities have happened without an apparent cause "Panic" may be the catchall explanation but we suspect that respiratory shock can be the true cause for the panic and the real cause of the problem. Certainly anyone who has observed a diver experiencing severe respiratory shock would see it as panic. The diver, if they survive, may be confused and interpret the event as a sudden mechanical blockage of regulator gas/air flow, since there is little awareness in the SCUBA diving community of respiratory shock, let alone identifying the event. When a diver is using Helium in the breathing mix the danger is compounded. This is due to the greater heat transfer characteristics of Helium mix at depths where this mix is used. A technical SCUBA diver using Helium in the breathing gas mixture switches to this mix from a nitrogen mix during descent, usually deeper than 100 ft. (30.5 M). At these depths the water temperature can be below 40° F (4.5° C). The tank of Helium mix would be full. If 3000 psi (206.8 Bar) were the tank pressure, the first two or three inspirations would be at minus 10° F (minus 23.3°C) with even lower temperatures of the inspired gas with the continued reduction in temperatures of the metal breathing regulator system caused by the refrigerator effect of the first stage regulator. It is not known at what temperature respiratory shock occurs in divers and it undoubtedly varies from diver to diver. We believe that minus 10° F (minus 23.3°C) on any gas including air, but especially Helium mix, is cold enough to cause a serious danger to any diver. This means any diver in water that is below 45° F (7.2° C) or so, can be on the threshold of respiratory shock if their breathing source is a SCUBA tank of compressed gas/air. If breathing mix is stored at 6000 psi (413.7 Bar) the temperature of the inspired gas to a diver in 40° F (4.5° C) water can be around minus 60° F (minus 51.1° C). In cold water technical SCUBA diving, switching over to a tank of HeliOx that is stored at 6000 psi (413.7 Bar), in our opinion, can be extremely dangerous. High percentage Helium mixes in deep commercial diving require the incoming gas temperature at the diver to be above 100° F (37° C). Below that the diver’s time underwater is shortened in direct proportion to the lowering temperature of inspired gas. The deep commercial diver that experiences interruption of gas flow in their umbilical must switch to emergency gas, which is usually an open circuit system, supplied by a high pressure SCUBA tank/s. If the hot water flow is also interrupted the diver will receive only very cold gas from the tank/s. This is a very dangerous situation. From the above information the obvious solution to the problem is to heat the breathing gas/air of any deep water or cold water SCUBA diver. Deep water or cold water commercial divers as well should heat emergency gas/air that is supplied from high-pressure tanks worn by the diver. Power is necessary to do the work of heating. We believe that we have a potential solution to this problem in the works at Kirby Morgan Dive Systems and will publish the results when they are available. Many years of sport SCUBA and commercial diving in moderately cold water have been done seemingly without problems from cold gas. Careful observation and awareness by divers can help all of us understand how cold breathing gas affects us. © 2000 and 2001 Kirby Morgan Dive Systems, Inc., All rights reserved. Do not copy without written permission |