In evaluating the problem of atmospheric hygiene aboard ship one must keep in mind the following dictates quoted from the Bureau of Ships Manual: “The weight added, space occupied, and the power consumed by the ventilation, heating and living arrangements on a Naval vessel must be at the expense of other military necessities. The minimum of equipment is provided which will accomplish the following purpose:
(a) Maintain in the living spaces and normally occupied parts of the vessel conditions which will keep personnel fit to fight under the strain of frequent watches during prolonged wartime cruising;
(b) Maintain at battle stations and in working spaces conditions which will keep personnel physically fit to fight and mentally keen under the circumstances when such spaces must be occupied during war.
Basically, the environment must be such that the body can maintain proper heat balance, and the chemical composition of the air must be such that it contains no harmful components and provides a sufficient quantity of oxygen.”
The methods of meeting a Naval emergency by a rapid increase in personnel aboard ship, lengthened periods in forward areas, and sacrificing personnel space for storing Naval ordnance, all place considerable stress on the crew. One way in which these stresses may manifest themselves is by increasing the number of incapacitations from disease or altered resistance to infection exhibited partly in lowered resistance in the membranes of the nose and throat, which results from vasomotor shifts of blood in the internal organs.
Our problems of providing ventilation, water, light, means for disposal of waste, and preservation of food are all inter-related when the ship is operating under conditions necessary for maintaining a watertight integrity during cruises of long duration in tropical waters.
Considerable physiological psychrometric data have been obtained on men at work at high temperatures both in the laboratory and in the field. Information, however, is meager concerning the men exposed to continuous hot environments over a number of days. Under the special requirements of present day Naval operations, it is not uncommon for ships to operate many days or months at a time completely secured; that is, with ventilation for the entire ship supplied only by air ducts. Modern warships produce thousands of horsepower, most of which energy is transformed into heat. Consequently, the internal temperatures of the ship are higher than the outside air and the temperature remains approximately constant day and night.
Another problem has been the aircooled hospital ships, which became a recognized necessity in tropical areas for the proper treatment of patients. Although statistics are not at hand to indicate the rate of deaths and retarded recoveries of patients in ships not aircooled operating in tropical areas, medical officers on such ships have reported that high temperatures and humidity are major factors in prolonging disability and in increasing mortality in the sick and injured. Even healthy men subjected continually to high temperatures show a large loss of fluid and salt and an increased pulse rate indicative of vascular stress.
Experiments were set up at the Naval Medical Research Institute and completed by Pace, White, Fisher and Birren, to study the effect of hot as contrasted with cool sleeping quarters on men working during the day in hot environments, and to study the problems that I have indicated. These experiments were carried out on two groups of men subjected to different conditions of environmental temperatures. Both groups worked in a hot environment, but one group rested in hot quarters which provoked sweating, whereas the other group rested in quarters cooled just below the sweating threshold temperature. The group resting in cooled quarters showed better overall performance.
Examination of such diversified functions as sensory motor performance, various aspects of vision and the performance of physical work in the heat, consistently demonstrated the superiority of the cooled group.
Clinical observations indicated that the physical condition of the men resting in cooled quarters was better than that of the men resting in hot quarters. It was also evident that men in hot quarters were under greater psychological stress. Probably the principal factor underlying the difference shown by the two groups was the amount of sleep they were able to get in cool quarters as contrasted to the sleep in warm quarters.
Statements obtained from the men of both groups indicated that those in cool quarters slept better; itching caused by heat rash, which was almost universal in the group resting in hot quarters but negligible in the group occupying cool quarters, may also have been a factor. It was concluded that men forced to work in a hot space will perform most tasks significantly better if they are provided with cool rather than with hot living and sleeping quarters.
In another similar experiment conducted at the Naval Medical Research Institute by Pace, Fisher, Birren, Pitts, White, Consolazio and Pecora, two groups of six men each lived in a temperature environment of approximately 85 degrees Effective Temperature, dry bulb 90° Fahrenheit, wet bulb 83°F., for 9 hours daily. One group, the hot or continuous exposure group, remained at this temperature for 12 hours at night. The other group, the cool or intermittent exposure group, was removed to an Effective Temperature of approximately 75 degrees, dry bulb 80°F., wet bulb 70°F., during the 12 hours at night. Both groups spent the 3 hours remaining in each day at an Effective Temperature of approximately 90 degrees, dry bulb 108°F., wet bulb 83°F., during which time they performed treadmill work tests. The men were exposed to these conditions for 30 days. The period of heat was preceded by a control period of 8 days, and was followed by a recovery period of 6 days. During these periods both groups lived continuously in an ambient Effective Temperature of approximately 75 degrees.
Physiological and psychological test batteries were administered daily to the two groups and a clinical examination conducted 3 times a week. The hot group exhibited extensive heat rash, which first appeared on some individuals within 3 days of exposure to the heat and continued throughout the 30-day period, whereas the cool group experienced nearly complete freedom from heat rash. The mean basal rectal temperature of the hot group was approximately one degree Fahrenheit higher than that of the cool group; the mean pulse rate was about 4 beats higher than that of the cool group; the water loss during the night was approximately double that of the cool group. On the basis of reports on the subjects and the impression of observers, the cool group showed greater ease of going to sleep, more spontaneous activity, and greater alertness. None of the sensory motor functions tested, and only a few of the physiological measurements, showed a difference between the two groups. Hence it was concluded that men 18-21 years of age can tolerate an effective temperature of 90 degrees for at least 30 days with very little evidence of deterioration. However, they do so at a somewhat higher physiological cost which might lead to deterioration with longer exposures. It may also be concluded that heat rash, which invariably develops under these conditions, can be prevented by daily part time cooling of 12 hours or less.
Very important studies were carried out during the past year at the Naval Medical Research Institute by Behnke and Consolazio on carbon dioxide and oxygen alteration pressures. In tests to study the effects of recirculated air conducted for periods as long as 72 hours in a sealed laboratory room, and for periods as long as 60 hours in submarines alongside of a dock, and 50 hours in a submarine at sea, it was found on a basis of 500 cubic feet of air volume available per man that:
(1) Carbon dioxide will reach a concentration of 5 per cent at 35 hours and that it can readily be controlled for an additional 25 hours by means of soda lime absorption utilizing a blower system;
(2) Oxygen will decrease from 21 to 15 per cent at the end of 35 hours and to 12 per cent at the end of 60 hours;
(3) Under these conditions of elevated carbon dioxide and reduced oxygen concentration, personnel are able to perform their duties proficiently. Biochemical, physiological and psychological tests show no incapacitating effects. Minor symptoms of headaches, nasal congestion and dryness of the throat were followed by quick recovery when exposed to outside air;
(4) For periods of emergency the present limit of 3 per cent of carbon dioxide and 17 per cent oxygen can be changed to 5 per cent carbon dioxide and 13 per cent oxygen and still maintain an effective oxygen pressure in the lungs and blood and tissue. The mechanics in part responsible for the oxygen equivalent change is a two-fold increase in breathing volume, which result? from the rise of carbon dioxide from 3 to 5 per cent. It is the more effective ventilation of the lungs and the increase of circulation rate that permits the decrease of ambient oxygen from 17 to 13 per cent without a corresponding reduction in oxygen pressure in lungs, blood and tissue.
The importance of this work is obvious when we consider that, without increasing space or weight, the period of submergence during emergency may be extended for as long as 50 hours and probably to 60 hours, when the occasion arises for such use.
Aboard Naval vessels the problem of odor control is a real one due to the ships being secured during days of battle conditions. The odor index becomes increasingly higher with operations.
Physiological odors affect the appetite, efficiency and morale of all hands. Yaglou has pointed out the value of using odor as an index of air quality. He found that the odor index, as employed by trained observers, was a better criterion of air supply per person in a space then the carbon dioxide concentrations.
In enclosed spaces intended for human occupancy the process of air conditioning controls simultaneously the temperature, moisture content, movement and quality of the air. In regard to air qualities, it is generally accepted that when the only source of contamination is the human occupant, the minimal quantity of outdoor air needed is that required to remove objectionable body odors and tobacco smoke. Other factors, such as oxygen, carbon dioxide concentrations, bacterial contents and dust solutions, are also to be considered.
As weight and space are critical, a minimum quantity of outdoor or replenishment air must be supplied to these spaces if air conditioning of these spaces is to be incorporated in the design of ships. It is well known that the odor level in a space depends upon a number of factors, including characteristics of the environment, dietary and hygienic habits of the occupant, the amount of outdoor air supplied, whether smoking is permitted, the space allowed per person, the capacity of the wet coil cooling surface to remove odor, the temperature and relative humidity.
A research project was set up at the Naval Medical Research Institute and completed by Consolazio and Pecora to determine the minimal quantity of outdoor replenishment air required to keep odors within an acceptable limit. A simulated battleship compartment was utilized and considerable care was exercised to reproduce conditions aboard ship. The employment of a liquid chemical and ozone as deodorants was also evaluated. As the result of these experiments, it was concluded that
(1) With air cooling alone, 5 cubic feet per minute per man of replenishment air will keep odors at an acceptable level. The condensation of water on cooling coils is associated with the removal of odors. The quality of air under these conditions is similar to that attained when 53 cubic feet minutes per man of replenished air are introduced by simple ventilation without air cooling;
(2) With activated carbon, replenishment air can be further reduced as low as one cubic foot minute per man;
(3) The liquid chemical deodorant and ozone employed in separate tests did not reduce odor levels. Exposure to these substances, however, after a period of 10 minutes, apparently exerted an anesthetic effect relative to odor perception;
(4) A chemical method based upon the reduction of an acid potassium permanganate solution by organic matter in the air proved to be of value in determining the amount of tobacco smoke present. The result, however, could not be correlated with the amount of other odoriferous substances present.
(5) Carbon dioxide, carbon monoxide, bacteria and dust did not reach objectionable or noxious levels even at 1 cubic foot per minute per man replenishment air volume.
Later studies were carried out on 6 commercial odor control agents; and of all of these tested, only activated carbon was proved to be effective.
Another very real problem encountered in the Navy when operating in tropical areas, under conditions of high temperature, is heat rash. This condition results in the loss of many man days spent in the sick bay and a general lowering of efficiency and morale. If the condition is allowed to persist under unhygienic conditions, secondary invaders of the skin cause cellulitis of a proportion dependent on the virulence of the invader and the resistance of the individual.
This problem became so serious during the early part of the war that a research project was set up at the Naval Medical Research Institute and completed by Blum, Gersh and Spealman, to study the skin effects of hot environment on man.
Four groups of volunteers were used. It was found that by subjecting them to temperatures of 108 degrees Fahrenheit dry bulb, and 83°F. wet bulb, at an Effective Temperature 90° for 24 hours per day, the rash would appear as early as 72 hours. When subjects were allowed to spend 17 hours or more per day in a cool environment, the incidence of heat rash was greatly reduced.
Heat rash was found to be a rapidly reversible condition if it was subjected to a cool environment when it first appeared. Neither pressure nor friction nor the inhibition of sweating by formalin prevented the development of heat rash. Cold baths appeared to have a slight ameliorating effect. Previous exposure to ultra-violet radiation inhibited the development of heat rash in some cases. There was an increase of white blood cell count with a relatively lymphocytosis in all cases where blood counts were made. Changes in hydrogen ion concentration of the sweat were not associated with heat rash. No changes were found in the elasticity of the skin, in the rate of histamine wheel formation, or the disappearance of the saline wheel.
The lesions that were observed to occur after exposure to hot environment are best described as a papulo vesicular rash, varying considerably morphologically from individual to individual. There would appear first a macular erythema which was followed by papules and vesicles and then by pustules. The fluid in the vesicles were clear at first, and after 24 hours would become cloudy. Culture of the clear fluid revealed no bacteria except in rare instances, in which the organisms were probably introduced from the surrounding skin surface. When the vesicles erupt, the secondary invaders usually enter and a pustule forms.
The lack of evidence of primary infection and the universal appearance of the rash in all subjects when temperature conditions are sufficiently severe, lead to the conclusion that heat rash is primarily a physiological problem. It would appear from this study that heat rash may be kept to a minimum if the individual is permitted rest in a cool environment when off duty. It also emphasizes the necessity for personal cleanliness to prevent the occurrence of pustular lesions when the vesicles erupt.
An associated problem concerning high temperatures frequently encountered, especially in engine spaces in operations in the tropics, involves the physiological reactions resulting from loss of body fluid by men exposed to high temperature for varying periods. Large quantities of salt are lost in the sweat produced to maintain body temperature. If this loss is replaced by water alone, the concentration of salt in the body fluid decreases to the point where heat cramps result.
The amount of salt lost through sweating depends on the degree of acclimatization, the amount of work done, and the Effective Temperature. As high as 8 quarts of fluid may be lost in a 24-hour period. One-tenth to five-tenths per cent of this is salt. While it is desirable to replace this salt loss by increasing the amount of salt in the regular diet, this cannot always be accomplished.
It has been standard practice for some time to have automatic vending machines containing salt tablets located throughout the ship. Personnel are instructed to use this salt in quantities depending upon their activity and the temperature in which they are working. The method of adding salt to the drinking water has not proven satisfactory. It is a common complaint of men using these salt tablets that they are made nauseated by their ingestion. Medical officers frequently see cases of vomiting and resulting gastric distress.
Due to prolonged operations in the tropics, a research project was undertaken at the Naval Medical Research Center and completed by Consolazio, Pecora, and Pfeiffer, to develop a salt tablet that would not cause nausea and vomiting and gastric distress. The workers originally worked on the premise that if they could develop a salt tablet that would dissolve readily and go into solution immediately, the time of resulting gastric irritation would be shortened and the symptoms would be lessened. Experimental work demonstrated that this was not the case and that shortening the time the salt was in the stomach increased the severity of symptoms.
Work then proceeded in developing a tablet that would have a prolonged effect or a slower rate of disrupting. Various forms of coating the salt tablets were first tried. These measures were not effective and were found to be unsatisfactory, as once the coating was acted upon by the gastric secretions absorption of salt was rapid. Various collodion membranes were then tried and finally it was discovered that by using cellulose acetates or nitrates, an impregnation of the salt tablets was achieved that would give a uniform prolonged disrupting time. Structurally the cellulose acetate or nitrates penetrate the tablet, forming a honeycomb structure a- round the salt granules. As the salt dissolves, the impregnating film breaks away and liberates the free salt. When the salt is completely dissolved, the cellular stroma of the impregnating film remains.
Experimental work in vivo and vitro demonstrated that the tablet would dissolve in approximately 80 minutes. Further work showed that this tablet caused very little distress compared with the currently used fast dissolving salt cornstarch tablet and the formerly used pure salt tablet. Work was then carried out which demonstrated that the cellulose stroma of this impregnated salt tablet would pass through the gastrointestinal tract harmlessly.
Further work showed that the impregnated tablet would withstand high temperatures and humidity encountered aboard ship and under tropical conditions. The tablet could be made without difficulty by mass production. This tablet is now in the process of receiving U. S. Federal specifications.
Under the impetus of war, many research projects were initiated that have advanced atmospheric hygiene in the Navy. Now that the necessity for such work is not so apparent and personnel are being demobilized from our Research Centers, it is presumed that research will, if not encouraged by additional personnel and facilities, go back to its former level before the war. The need for continued research in atmospheric hygiene is especially great because of our present global operations. Surface ships, submarines and aircraft operate all over the world for protracted periods of time. Many of the problems that we have had in submarines and surface craft in atmospheric hygiene are having their counterpart in aviation and are being complicated by problems of high altitude and anoxia.
1. The opinions or assertions herein are the private ones of the writer, and are not to be construed as official or reflecting the views of the Navy Department or the naval service at large.