Abstract
Heat stress is a common condition in hot climates. Aviators are the most affected based on the nature of the work they do. Desert climates such as the Arabian Peninsula pose a challenge to aviators. This research paper seeks to investigate the occurrence of heat stress in flight cockpits in desert climates. Besides, it makes a comparison between sources of heat on the performance of the pilot. The methodology used is an article review. The articles used were compiled from PubMed. The results show that heat stress has physiological and psychological effects on aviators and that the cockpit had different sources of heat depending on the ‘make’ of the aircraft and the climate. Clothing and height of flight are also important factors in the etiology of heat stress. The paper concludes that although the effects of heat stress on modern aircraft are subtle, they may greatly affect the performance of aviators in the cockpit. Therefore, recommendations are provided on how to prevent heat stress, including the development of better cooling systems and indices.
Introduction
The Middle East and Arabian Peninsula Climate
The Arabian Peninsula has a relatively hotter climate compared to the rest of the world. It is one of the hottest places on earth (Perry, 1967). Working in this environment requires one to make adequate adaptations. Despite the hot climate, the area also has millions of inhabitants in different occupations, with the aviation industry being vibrant. Temperatures in the Middle East are often above 30oCelsius. There is rarely any rain since the region has only one rainy season. The Arabian Peninsula is also categorized as a desert since there are inadequate natural water resources. The area is largely arid and semi-arid. There is often a lack of water and high temperatures (Perry, 1967).
The Middle East has mild winters once a year. However, the rest of the year is characterized by hot and dry weather (Perry, 1967). The region where the climate is different is in the mountains that form part of northern Iraq and Iran, and part of Eastern Turkey (Perry, 1967). The winters are long in this region, with temperatures dropping to below the freezing point in some areas. The monsoon that is frequently experienced in the area results from the hot and dry climate. The winds blow towards the land in one part of the year, with the reverse taking place when the temperatures on the land drop (Perry, 1967).
Temperatures above 100 F are common. However, the average recorded temperatures are 85 F for the whole region (Perry, 1967). Basra has some of the hottest temperatures in the Middle East. These temperatures are recorded to reach above 124 F (Perry, 1967). Another common phenomenon in the region resulting from the high temperatures is the sandstorms that the area experiences frequently. This phenomenon results from the collection of dust and sand from the desert surface by the strong winds blowing across it (Perry, 1967).
Arabia Area Climate
Different researchers have ventured into the study of the effects that the Arabian climate has on the different professionals working in the area. However, few researchers have documented the effects of the area’s climate on aviators, especially pilots (Perry, 1967). In one of these studies, the researchers sought to identify the effects of South Arabian Climate on army pilots (Perry, 1967). The results indicated that the area is particularly harsh to pilots in the army (Perry, 1967). The study was carried out through personal interviews, questionnaires, and reviews of medical records.
The Arabian climate is described as being rough for pilots, with documented cases of heat and cold stress in the course of operations of this personnel depending on the part they are working from. The aviation industry in the Middle East is rapidly evolving. It is currently a major part of the global aviation industry. The area is also home to many types of aircraft, with some being more susceptible to the elements in relation to others.
Heat Stress: Definition and Measurements
Heat stress is a condition in which the body is unable to maintain its temperature to the normal range after the environmental temperatures rise above certain levels (Razmjou, & Kjellberg, 1992). In normal individuals, a small rise in temperature causes sweating, which is a physiological reaction. However, in heat stress, the body is unable to cool itself through this process, resulting in several heat-induced illnesses (Razmjou, & Kjellberg, 1992). The heat-induced illnesses that occur in heat stress include heat cramps, exhaustion, and heat stress, which is the most severe of them (Razmjou, & Kjellberg, 1992).
Heat stress is a medical emergency that leads to the elevation of body temperature above levels that the body cannot control. Heat stress is often preceded by heat exhaustion, which is the elevation of temperatures in the body because of dehydration in the presence of high temperatures (Nunneley, & Myhere, 1976). Heat cramps are similar to any other type of cramps in the body. They are caused by working in extremely hot environments with resultant electrolyte imbalance (Nunneley, & Myhere, 1976). When sweat does not evaporate because of the high humidity in hot conditions, it may wet the clothing attire. The sweat may interact with the skin and result in heat rashes, which comprise another common component of heat stress.
There are many causes of heat stress in the body. They include dehydration in a hot environment, exposure to the sun, limited cooling in hot conditions, physical exertion, bulky dressing, the poor state of health, pregnancy, some medications, high temperatures, and humidity. The most important of them is exposure to hot conditions. The measurement for heat stress is possible through the estimation of body temperatures (Razmjou, & Kjellberg, 1992).
The Wet Bulb Globe Thermometer (WBGT) is the best measure for environmental heat stress. This measure incorporates humidity, the flow of air, and the ambient temperatures (Razmjou, & Kjellberg, 1992). Some of the other components in heat stress that may be measured independently include the wind speed, the humidity, and the estimation of the heat index. The measures provide an accurate way for heat stress estimation. The calculation allows for the estimation of the degree of heat stress.
Physiology of Heat Stress
Four basic mechanisms of heat transfer in the human body are known to include convention, radiation, evaporation (convention), and conduction (Nunneley, & Myhere, 1976). Evaporation and conduction are the main methods through which the body loses its heat. However, temperature gains can be by any process. The heat equation that is frequently used to explain the body temperature is a factor of all the processes. The core body temperature results from the interaction between the various processes of heat transfer. The difference between the heat gained by the body through conduction, radiation, convection, and convention and that lost through the same process contributes to the final standard body temperature.
In heat stress, the body temperature considerably rises and may exceed the ability of the various cooling mechanisms in place (Ailnut, & Allan, 1973). When these mechanisms are overwhelmed by the increase in temperature, the body cannot control its temperature. Hence, there is a rapid rise in the core temperatures. The rise in temperature interferes with the normal body processes that require a constant temperature to operate, with respiration being among the most affected processes (Ailnut, & Allan, 1973).
Aviators and Heat Stress
Heat stress is a problem for aviators, with pilots suffering from the condition in their pre-flight duties and/or while flying planes that are not air-conditioned such as helicopters (Perry, 1967). The aircraft characteristics combine with the humidity, ambient temperatures, and radiant heat, and wind speeds to cause high body temperatures and resultant heat stress (Sen-Jacobson, 1959). The aviation pilots, especially the army pilots, are forced to wear clothing and other gadgets to optimize their functioning. This situation also contributes to the rise in ambient temperatures (Perry, 1967).
Fatigue and elevated metabolic rates may cause the alteration of the body temperature regulatory ability for aviators, hence leading to heat stress. Many types of research done on the temperatures in some aircraft, especially helicopters, found that there were persistently raised body temperatures for these individuals. In some of the research findings, the elevated temperatures in cockpits are a result of the external high temperatures and the internal heat sources such as engine power, auxiliary power, and the electronic systems in the aircraft (Ailnut, & Allan, 1973).
Another major contributor to the high temperatures in the greenhouse effect (Perry, 1967), which will be discussed later. Studies that have evaluated the effects of heat stress on pilots have established a degree of reduction in cognitive performance for aviators (Ailnut, & Allan, 1973). The pilots also had disordered vigilance and time estimation, with an overall reduction in the reaction time (Perry, 1967). The effects of heat stress on the performance of aviators are important to evaluate, and hence the importance of this research.
Sources of Heat in a Cockpit
The cockpit takes different designs and shapes depending on the type of aircraft that is being discussed. There are differences in the materials that make the cockpit and the position of the different windows in the different aircraft. The sources of heat in any cockpit are dependent on the design of the cockpit and the involved four processes of heat transfer. The most significant of the sources of heat in the cockpit is the sun where solar radiation enters the cockpit from different sides (Nunneley, & Myhere, 1976). The windows and the front screen are the main areas where solar radiation enters the cockpit (Ailnut, & Allan, 1973).
The sun causes the air within the cockpit to be heated to temperatures above the normal, hence predisposing it to heat stress (Nunneley, & Myhere, 1976). Solar radiation that penetrates the aircraft’s body warms the sections of the aircraft that are not covered with opaque materials. The result of exposure to solar radiation is heating of the cockpit components, which in turn transmit the heat to the pilot and air in the same cockpit (Ailnut, & Allan, 1973). The pilots are also heated directly by solar radiation, with the result of this situation being the increased body temperature. When the plane is flying in the direction of the sun, or when the sun is directly overhead, the solar radiation is experienced most. The amount of cloud cover is important in the determination of heating from the sun (Ailnut, & Allan, 1973).
The cockpit is mostly equipped with instrumentation to aid the pilot and the flight engineers in their occupation. These components run on energy. Most of them produce considerable amounts of heat resulting from friction or resistance to the flow of electric current (Gibson, Cochrane, Harrison, & Rigden, 1979). Without proper insulation, the instruments in the cockpit produce enough heat to raise the temperatures in the cockpit. This may act in concert with the other sources of heat to cause heat stress. The engine in some aircrafts such as helicopters may also be a source of heat to the cockpit (Gibson, Cochrane, Harrison, & Rigden, 1979).
The other source of heat in the cockpit is that generated by the pilots because of the normal metabolic processes. When pilots are actively performing their duties in operating the aircraft, respiration rates increase, thus causing the production of heat. This heat may warm the cockpit via radiation and conduction and other methods of heat transfer. If the pilot is dressed in many types of attire or has different gadgets on the body, the body heat generated by radiation is not lost. Hence, the result is an increase in the core body temperatures (Gibson, Cochrane, Harrison, & Rigden, 1979). The clothing that the aviators wear also determines the conduction of heat away from the body, resulting in cooling. However, this cooling is interfered with if the pilots wear clothing that does o permit heat loss.
Greenhouse Effect
The greenhouse effect is a cause of raised temperatures in the cockpit of some types of aircraft. According to Perry (1967), this effect occurs in closed cabins. It is known to exacerbate the rise in temperature from other sources in the cockpit. The greenhouse effect is known to occur in cabins that have windows that are relatively opaque to long wavelengths (Perry, 1967) in the cockpit. The solar radiation causes heating of the internal surface in the cockpit, which transmits heat through the process of radiation (Perry, 1967). Since the windows are opaque to the long wavelengths emitted by the surfaces, they are reflected back to the cockpit, hence resulting in the amplification of heat in this space (Perry, 1967). In the cockpits that experience the greenhouse effect, the ambient temperatures have been measured to be higher than other cockpits.
The cabin air also affects the rise in temperature that is observed in the cockpits. According to Perry (1967), the rate of absorption of heat by cabin air is increased by the increase of humidity and carbon dioxide in the cockpit. The measurement of the WBGT heat stress index in cockpits reveals that the greenhouse effect causes significant heat stress (Perry, 1967). The high humidity in the cockpit that leads to the greenhouse effect comes from the respiration and sweating of the occupying pilots, with the respiration also leading to increased carbon dioxide that further worsens the greenhouse effect (Perry, 1967).
Avionic-produced Heat
Avionic-produced heat is also a major contributor to heat stress in aviation pilots during their work (Harrison, & Higenbottam, 1977, p. 522). Harrison and Higenbottam (1977, p. 522) state that although the measurement of avionic-produced heat is difficult, the combination of these forms of heat with solar radiation causes high temperatures. The heat produced from avionics varies from one type of plane to the other. The measures are difficult to estimate. The instrumentation in modern aircraft is a major source of avionic heat. There has been a challenge with the reduction of this heat, especially in the helicopters.
Clothing
The clothing that pilots wear is an important determinant of heat stress and the frequency with which this stress occurs. Aviators usually wear different types of clothing depending on the prevailing weather conditions in the departure airport. The weather may be different at the airport where they land. In some of the researches done to establish the effects of clothing on heat stress, the researchers observed that there was a pragmatic increase in the body temperatures of individuals who wore certain types of clothing (Pellerin, Deschuyteneer, & Candas, 2004, p. 717).
Pellerin, Deschuyteneer, and Candas (2004, p. 717) state that the insulation that pilots get in the flights is due to the number and type of attire that they wear in their workplace. The clothing may inhibit the evaporation of sweat, thus leading to elevation of the pilots’ body temperature. Developments in the aviation industry have led to the introduction of new clothing that is supposed to protect the pilots while aiding in their work by increasing efficiency (Pellerin, Deschuyteneer, & Candas, 2004, p. 717). However, this clothing is a significant source of insulation for the pilots as they operate in hot conditions, thus contributing to the increase in body temperature and hence heat stress.
Different Environment, Locations, and Time of the Year
The temperature inside a cockpit varies with the environment, the location, and the time of the year. The weather is known to change in different parts of the year, with summers and winters occurring at different times. The seasonal variation of weather in line with the climate of an area is an important factor in the determination of how high temperatures in a cockpit will be (Perry, 1967). The location of an aircraft determines the temperatures that the cockpit is recording. Therefore, the Sahara desert will record higher temperatures than other parts of the world. The time of the year is also important. Pilots have to plan their journey while keeping this in mind. Among the most significant areas in terms of heat stress are deserted, which are important to discuss since the Arabian region is also mainly arid. In one of the researches evaluating the impact of the environment on their performance, Cardwell (1992) described heat stress as a major factor in the Persian Gulf war of 1991. The weather in this region was harsh to the servicemen operating here at that time. Pilots were treated for heat stress.
Desert
The arid region is one of the uncaring environments in the world. This climate has been known to trigger heat stress in many individuals. Many airports are located in the desert climate, with planes having to fly, land, and take off in these places (Perry, 1967). In the changes that have taken place in the aviation industry, planes are kept waiting for some time before takeoff. Most air conditioning systems are inefficient for stagnant planes (Cardwell, 1992). Therefore, planes in desert conditions are exposed to high temperatures even before takeoff. Cardwell (1992) describes the desert environment of Iraq as one of the places that the American military experienced heat stress.
Materials and Methods
This research was an article review. The benefits of using an article review over other forms of research include the shorter period required to carry out the research, the accuracy of information from other researchers, and the efficient utilization of resources. After the main objectives of the study were developed, the step that followed in the methodology was the search for articles to be used in the review. The keywords chosen for the search included heat, aviation, pilot, helicopter, and cockpit. After the determination of the keywords in the search, an appropriate database was selected for the search. The database that was selected for the search was PubMed. This site provided the best results of peer-reviewed articles.
The initial search produced over 100 articles using the keywords. These articles were later sorted to evaluate the most applicable ones. An inclusion criterion was used in the selection of articles. The basic rule is that they had to be written in English. To allow comparison of the various effects of heat stress, articles focusing on the heat stress in different aircraft types such as helicopters were chosen. The other articles that were selected in the search included those that discussed different situations, locations, environments, and climates. These articles were selected to help in the discussion of the subject from different angles.
The other criterion used to sort the articles is the use of factors, sources, or situations producing heat stress on the crews. These were compared with regard to the effect they leave on the performance of cabin crews and their operation endurance ability. This resulting research paper tries to compare the effect of the heat stress sources and different situations on pilot performance and comfort in a cockpit and the physiological and psychological effects of heat stress. It focuses more on the helicopter cockpit by comparing it with the other types of aircraft.
Results
Helicopter vs. Fighter Cockpit
The literature provided the differences between the different types of aircraft in relation to heat stress. In research by Breckenridge and Level (1970), the AH-IG helicopter was found to have increased temperatures in the cockpit. These temperatures predisposed pilots to experience heat stress. The helicopter is one of the types of planes that have a higher risk of heat stress compared to other types of airplanes. Some of the reasons that make this type of aircraft more predisposed to high temperatures include the heat dissipated from the engine and the absence of air conditioning among other factors (Breckenridge, & Level, 1970).
The helicopter cockpit is closer to the engine compared to other types of aircraft. This exposition may reveal higher ambient heat. Breckenridge and Level (1970) recommended that the helicopter models they studied be fitted with air conditioners to prevent any form of heat stress. In their research, they found that there was increased sweating in the cockpit of the helicopters, more than it was experienced in other forms of aircraft (Breckenridge, & Level, 1970). The other type of aircraft that the pilots and other aviators operating it were susceptible to heat stress is the fighter aircraft. According to Nunneley and Myhre (1976), unlike other aircraft that are completely covered with opaque materials except for the windows, the fighter aircraft have bubble canopies to improve vision, and hence the main cause of high temperatures inside the cockpits of fighter aircraft.
In fighter planes that are in flight or waiting on the runway, the exposure to sunlight causes increased radiant heat load. The sun directly heats the skin of the fighter pilots. The air inside the cockpit is also heated. The glass contributes to the greenhouse effect (Nunneley, & Myhre, 1976). Ventilation in the fighter planes is enhanced through the installation of air conditioning, although the pilots are still vulnerable to heat stress (Nunneley, & Myhre, 1976).
Type of Exercise heavy vs. Light
The type of exercise that the aviators are carrying out is an important determinant of heat stress as earlier stated. Heavy exercise causes the use of a high respiration rate in the pilots, resulting in an increase in temperature and sweating (Harrison, Higenbottam, & Rigby, 1978). When a pilot is carrying out a heavy or difficult maneuver, he or she may use a lot of energy in the process. This situation is known to be a significant source of body heat (Harrison, Higenbottam, & Rigby, 1978). If not adequately cooled, the body’s temperature may rise to a high level, thus resulting in heat stress and related conditions. The heat stress that is obtained in case of increased temperature results from the interaction between the radiant heat from the sun, the avionic heat, clothing, and instrumentation within the cockpit (Boutcher, Maw, & Tylor, 1995). However, there are cases where the body respiration rate may rise above normal without any predisposition such as disease.
Season and Climate
The climate that the aviators work in and fly in determines whether heat stress affects them or not. In cold climates, it is highly unlikely that pilots will get heat stress, with the most likely pathology being cold stress (Thornton, & Vyrnwy-Jones, 1984). Working in a hot environment such as flying across the Arabian region can precipitate heat stress. Pilots have to take adequate measures to prevent this occurrence (Perry, 1967). The Arabian climate is hot in most parts of the year. Pilots and other aviators in the region have a higher predisposition to heat stress as compared to other parts of the world (Thornton, & Vyrnwy-Jones, 1984). Seasonal variations are also known to cause a concurrent variation in the instances of heat stress. Some seasons such as the “summers” experienced in the Middle East have more cases of heat stress compared to other seasons.
Climate
The article review also identifies climate as a significant part of the factors determining the development of heat stress in aviators. As a rule, aviators working in a hot and dry climate are more predisposed than any other individual working in a cooler climate (Perry, 1967). However, heat stress can occur anywhere in the universe since the climate is not the only cause of heat stress (Thornton, & Vyrnwy-Jones, 1984). According to Perry (1967), the Saudi Arabian climate is one of the hottest climates in the world. The fortunes that have been realized in oil have meant that the aviation industry is well-performing. Some aviators working in this country have had to deal with the problem of heat stress, with a significant number of pilots who are new to the area having experienced heat stress at one time during their career (Perry, 1967).
Nunneley and Flick (1981) observed that the prevalence of heat stress in hot climates was high. In their research, they stated that pilots often have to deal with the high temperatures in hot climates (Nunneley, & Flick, 1981). According to Nunneley and Flick (1981), the planes get heat soaked even before they take off. Climatic heat input continues when they are flying at low altitudes. In cooler climates, the causes of heat stress may not necessarily be the climate, but other causes such as sickness and avionic heat (Caldwell, 1992).
Pilot Suits and Uniform
The clothing that aviators put on affects the retention of heat and the eventual development of heat stress. Aviators such as those in the army are required to put on special uniforms and suits that are designed to help them in their navigation to protect them from acceleration forces and accidents (Gaul, & Mekjavic, 1987; Vallerand, Michas, Frim, & Ackles, 1991). Reardon, Fraser, and Omer (1998) investigated the effects of thermal stress on the performance of helicopter pilots, with this stress being caused by aviator uniforms that they wore. The researchers concluded that there were minor effects of the uniforms on the cognitive performance of pilots who had occlusive dressings in their operations (Reardon, Fraser, & Omer, 1998; Zhang, Huizenga, Arens, Wang, 1987).
The core body temperature increases with an occlusive dressing and uniform for pilots. Therefore, Reardon, Fraser, and Omer (1998) recommended that helicopter pilots should avoid physiological stresses that may alter their performance. Gaul and Mekjavic (1987) are some of the other researchers who evaluated the effects of aviation suits worn by pilots on their performance. They reported that the commercial pilots were more affected by the heat stress due to their manner of clothing as compared to the military pilots (Gaul, & Mekjavic, 1987). The average flights for military pilots are 27% shorter in relation to those of commercial pilots. This finding may reveal the differences in the experienced temperature changes. Different types of suits exist for pilots. However, the suits have their own effects in relation to eat stress.
NBC Suits
One of the suits whose effects on the performance of people in flight were investigated is the Nuclear Biological Chemical (NBC) Individual Protective Equipment (IPE) (Thornton, & Caldwell, 1993; McLellan, Frim, & Bell, 1999). This suit was created to allow life-saving for aviators in the event of an accident. However, experiments conducted showed that survivors would be affected by the resultant heat stress if they landed in a hot area (Thornton, & Caldwell, 1993, p. 72). In the experiment conducted by Thornton and Caldwell (1993), the core temperatures of the individuals wearing the suits were reported to increase at a fast rate. In the event of an actual accident, the temperature rises and cause the eventual death of the victims, or cause them to abandon the useful suit (Thornton, & Caldwell, 1993, p. 73).
Anti-G Protection Suit
The acceleration forces acting on a pilot in a jet plane can affect his or her concentration by affecting the eyes and the brain. Special suits have been developed against these acceleration forces. These suits were studied to establish the effect that they have on the body temperature in hot conditions. Sowood and O’Connor (1994, p. 998) studied the effects of the newly developed anti +Gz suit that was meant to protect the pilots as they were in flight. The researchers compared the effectiveness of the new anti G system against previous versions of the same suit where they measured the core temperature of the wearers (Sowood, & O’Connor, 1994, p. 998).
The results of the experiments showed that there were significant increments in the core body temperatures for these individuals (Sowood, & O’Connor, 1994). The increased core body temperature was significant in affecting the cognitive performance of the individuals in the suits. Heat stress resulted in the case of extremes scenarios. However, there was a temperature rise in the participants, although the rise was inadequate to allow decreased cognitive functioning and eventual accident (Sowood, & O’Connor, 1994).
Low-Level Flights
The effects of low-level flights on the temperature inside the cockpit were the subject of some of the reviewed studies. The researchers evaluated the effects of flying at low altitudes on the core body heat and the cockpit temperatures (Bollinger, & Carwell, 1975). In the research by Bollinger and Carwell (1975), the flights were able to fly in hot conditions and in low altitudes. However, the temperatures recorded in the cockpit were higher than conventional flights in most cases. The research showed that low altitude planes have a significantly raised chance of experiencing heat stress as compared to the pilots that flew in high altitudes (Bollinger, & Carwell, 1975, p. 1225).
Ground Standby
According to Froom, Schochat, Strichman, Cohen, and Epsten (1991), the ground standby time for helicopters is often long. It may reach up to a period of one hour. The reason for the long standby time is to ensure that the helicopters can take off at the scheduled time. Froom et al. (1991) reveal that the high temperatures that are prevalent in most areas in summer may affect the cockpit while the planes are on standby. This situation may add to the stress in pilots. These researchers managed to show that there was an increase in the WBGT for pilots that remained on standby for about an hour in the airports (Froom et al., 1991).
Harrison and Higenbottam (1977, p. 519) were other researchers who obtained the same results as Froom et al. (1991) in their research. The researchers observed that the duration that the aircrafts remained on the standby state was proportional to the greenhouse effect to which the cockpit was subjected (Harrison, & Higenbottam, 1977, p. 523). Although the pilots would open the canopy partially during the standby times, the greenhouse effects were still evident, with temperatures in the cockpit increasing constantly. Therefore, the pilots were predisposed to an increase in temperature when they stayed longer on the runway waiting for their chance to take off.
Location in the Cockpit
The location of the aviators in the cockpit is significant in determining the extent of heat stress that they experience during flight. Nunneley, Stribley, and Allan (1981, p. 287) are some of the researchers who investigated the differences in temperature at the different parts of the cockpit (Nunneley, & Maldonado, 1983). In a fighter plane with two pilots, the rear seat was described as being hotter compared to the front seat, with the differences in temperature also being evident in the different heights in the aircraft (Nunneley, Stribley, & Allan, 1981). Therefore, aviators who sat in the back seat were more likely to be affected by heat stress as opposed to those in the front seat. The head level was also reported to be cooler than other lower levels in the aircraft. The differences in temperature were said to be a result of the cooling system that was being utilized (Bollinger, & Carwell, 1975, Nunneley, Stribley, & Allan, 1981, p. 290).
Discussion
Comparison of Different Sources of Heat in the Cockpit
The sources of heat stress in the cockpit were listed in most of the literature materials that were reviewed. Few of the researchers focused on a single source of heat in the cockpit. On rare occasions, they compared the different sources. The researchers measured the performance of the pilots and other aviators in relation to heat stress irrespective of its cause in the cockpit. The main source of heat in the cockpit recognized in the various studies is the radiation through the windshield. This source was recognized as an important influence on the performance of pilots (Nunneley, & Maldonado, 1983). The rate at which the decrease in performance occurred was more than exposure to other sources of heat.
For the helicopters, the second-largest source of heat in the cockpit was the engine heat. Pilots were significantly affected when these two major sources of heat acted in concert. Some of the studies investigated the effect of heat stress from the engine and its effect on the performance of aviators (Razmjou, & Kjellberg, 1992). The findings indicate that the effects are similar to those that occur from heat stress caused by other sources of heat. Aviators’ performance in these conditions drops significantly. As a result, they are vulnerable to accidents.
The source of heat that ranks third in the causation of heat stress to the aviators under simulation conditions is the mechanical and electrical equipment in the aircraft (Nunneley, & Maldonado, 1983). Aviators were found to be affected by the heat that was dissipated from the electrical and mechanical systems. The different studies used different measures of performance for the aviators. However, most of them provided similar results in the decrease in performance. The researchers also stated some limitations that would not allow room for comparison between the many sources of heat in the cockpit and their effect on the performance of the cockpit.
The other source of heat that was largely natural in the cockpit is the body metabolic process for the aviators. Pilots, just like any other individuals, have active respiration, which leads to considerable heat within the cockpit. The body has physiological mechanisms that are aimed at regulating the heat generated from the normal respiratory processes and external sources. However, there are situations where the body gets overwhelmed by the heat that is produced through normal respiration. This situation results in heat stress for the individual. This form of heat stress ranked after the above causes of heat stress.
Instrumentation also emerged as a significant source of heat in the cockpit. Most of the instruments in the cockpit use electricity. The resistance to the flow of the current in the wires used to operate the instruments results in the generation of heat. Although this source may be insignificant when compared to other sources of heat in the cockpit, it causes heat stress in association with the other sources identified above. This source of heat causes a significant reduction in performance for aviators, especially if they are forced to work in this environment for long hours. The comparison of the above sources of heat in the cockpit and their effect of heat stress on aviators can be done using a graph-based on information from the researches as shown below.
Physiological and Psychological Effects
The research reviewed the relevant literature on heat stress in pilots. Nunnely, Dowd, Myhre, and Stribley state that the effects of heat stress on the body can be measured through the estimation of different parameters. The measurements that are important in the evaluation of the results of the heat stress can be grouped in terms of mental manipulation, perceptual speed, and learning (Nunnely, Dowd, Myhre, & Stribley, 1978). Heat stress was demonstrated to affect these processes in normal individuals, with perceptual disturbances.
Nunnely, Dowd, Myhre, and Stribley (1978) showed that the only part of mental functioning that was not affected was the addition of columns. Learning was the most affected, with grave impairments in performance (Nunnely, Dowd, Myhre, & Stribley, 1978; Razmjou, & Kjellberg, 1992). Aircrew members are described in the research paper to be subjected to heat stress when flying and working in hot climates and when wearing some special suits. Therefore, the findings indicate that these individuals will be affected in their performance in these conditions.
Effects on Performance
Physiological (G Protection)
Nunnely and Myhre (1976) observe a number of physiological changes that occur before an individual succumbs to heat stress. There is an observed reduction in reaction time for individuals who are exposed to heat stress. This reduction may be fatal in the aviation industry that requires the aviators to have an intact, if not fast reaction time. Another physiological change is the rise in error rate in these conditions. While these changes are taking place, individuals usually do not realize and remain confident about their performance (Nunnely, & Myhre, 1976). The tolerance of aircrew to acceleration is also affected by the decreased perception occasioned by heat stress (Nunnely, & Myhre, 1976). Heat stress is also associated with marked sweating, which often results in dehydration, which worsens heat stress and G-tolerance for aviators.
Psychological Effects
The psychological effects of heat stress are described as subtle in most of the reviewed research (Nunneley, & Stribley, 1979). However, these psychological effects are dangerous to any pilot operating an aircraft. They can lead to accidents and other events. The psychological effects include decreased response time, decreased attention, cognitive defects, and reduced performance of motor activities. These skills are central to the aviation industry. Heat stress causes a reduction in their use. The result is the decreased performance of the aviators and eventual redundancy (Froom, Kristal-Boneh, Ribak, & Caine, 1992).
Cut-off Points and Limitations
The effects of heat stress on aviators, though described as subtle in most of the research, warranted a cut-off point that would assure the safety of the aircrew and their passengers. The Fighter Index of Thermal Stress (FITS) is a good example of a cut-off developed to control the exposure of aircrew to hazardous heat stress (Nunneley, & Stribley, 1979, p. 639). FITS is applicable as a scale for the control of the stress that is occasioned by hot climates. It minimizes the chances of developing the physiological and psychological effects that may compromise performance. The maximum safe thermal radiation load was also described. Aviators should be trained on how to observe and apply it to reduce the effects of heat stress (Davis, & Kaufman, 1963). The limitations of this study included the unavailability of current literature findings on the effects of heat stress on aviators, especially for different types of aircraft. The suggestion is that more research can be carried out in the future to compare the different models of aircraft and the different climates under standardized conditions.
Conclusion and Recommendations
Heat stress is established to be a significant cause of compromise for aviators. The factors that are important in the occurrence of this condition include differences in the type of aircraft and the different climates in which the aviators have to operate. The helicopters and fighter aircraft pilots are the most affected by heat stress. Sources of heat in the cockpit include solar radiation, avionic-produced heat, body metabolic heat, the instrumentation, and the engine heat.
The recommendations include that a maximum safe thermal radiation load and the Fighter Index of Thermal Stress should be more specific, with aviation industries being made to adhere strictly to it. The applied air conditioning systems must assure effective air distribution in the cockpit. Regulations should also be made for low-level flights in different aircraft in summer. These regulations should also focus on reducing the ground stand-by time for pilots. These measures need to be effective in reducing the chances of heat stress development.
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