thermal stress. 2 plan introduction factors causing heat stress effects of heat stress in aviators...

THERMAL STRESS

2

PLAN

• Introduction• Factors Causing Heat Stress• Effects of Heat Stress in Aviators• Factors Affecting Heat Tolerance• Heat Strain Parameters & Indices• Alleviation of Thermal Stress in Aviators• Conclusion

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ENVIRONMENTAL FACTORS AFFECTING AIRCREW HEALTH

VIBRATION

NOISE

CIRCADIAN DYSRHYTHMIA

RADIATION

THERMAL STRESS

HYPOXIA

DECOMPRESSION

ACCELERATION

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INTRODUCTION

• Optimum physical comfort of aircrew is important to ensure ideal man-machine combination in flying

• Thermal stress in aviators can be of two types:– Heat stress– Cold stress

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• Heat stress arises from an imbalance between a pilot’s metabolic heat production and his heat exchange with the environment

HEAT STRESS

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FACTORS CAUSING HEAT STRESS

• Climatic Factors Air Temperature - affects convection Humidity - affects evaporation Air Movement - affects convection & evaporation Radiant Heat - affects radiation exchange with body

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FACTORS CAUSING HEAT STRESS

• Aircraft Factors Aerodynamic Heating - due to friction between a/c & air Electrical Heating - due to a/c instrument & equipment Green House Effect - due to solar radiation

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FACTORS CAUSING HEAT STRESS

• Aircrew Factors Metabolic Heat - increases during flying ops Flying Clothing - in multiple layers causing interference with

evaporative & non-evaporative heat exchange Acclimatisation

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AIRCREW

• Psychomotor parameters

– Memory registration and recall

– Effect on attention and vigilance

– Increase in reaction time; reasoning & decision making

– Manual dexterity

• Physiological parameters

– Profuse sweating causing dehydration

– Reduced G tolerance

– Aggravate hypoxia

FAILURES

EFFECT OF HEAT ON AVIATORS

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FACTORS AFFECTING HEAT TOLERANCE

• Obesity• Lack of physical fitness• Fatigue• Lack of sleep • Dehydration• Fever & Illness• Lack of acclimatisation

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ALLEVIATION OF THERMAL STRESS

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ALLEVIATION OF THERMAL STRESS

• Station Policies• Pre-Flight Solution• In-Flight Solution• Personal Cooling Systems

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STATION POLICIES

• Ergonomics in design of flying station• Provision of air-conditioned building & transport• Aircraft to be parked in shade or use canopy cover• Use of mobile cold air units• Providing small fan inside cockpit with rubber blades

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• Better planning of sorties • Rotation of aircrew for sorties• Adequate interval in b/w sorties• Use of Heat Stress Indices to assess flying conditions:

– Wet Bulb Globe Temperature (WBGT): Universally accepted index to assess heat stress in warm climate

– Fighter Index Of Thermal Stress (FITS): Useful index in certain fighter aircraft during low level flying

STATION POLICIES

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• Physical fitness• Good work-rest schedule with adequate rest periods• Adequate hydration but NO alcohol• Balance diet before sorties• Appropriate clothing• Heat acclimatisation

PRE-FLIGHT SOLUTIONS – AIRCREW

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INFLIGHT SOLUTION

• Standby time on tarmac should be minimized• Avoid low-level high performance flying during day-time• Use of efficient Cabin Conditioning System

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CABIN CONDITIONING SYSTEM

• Effective way to combat heat stress• Limitations:

– Increases aircraft weight & reduces engine performance– Cabin noise– Localized cold/ hot spots– Ineffective at low altitudes

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PERSONAL COOLING SYSTEMS

• Cooling garments worn next to skin which permit flow of fluids to remove heat– Air-cooled Garments– Liquid-cooled Garments– Gel-cooled Vests

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• Air Ventilated Suit– Dry cool air is passed at pressure– Consists of piped lining inside

clothing material which allows evaporative heat loss

– Susceptible to contamination

PERSONAL CLOTHING

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• Liquid Conditioned Suits– Water through piped lining in

contact with skin– More effective– Difficult to maintain

PERSONAL CLOTHING

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• Gel Cooled Vests– New concept involving Flexum

material– Pre-refrigerated before use

PERSONAL CLOTHING

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TAKE HOME MESSAGE

• Know your body’s limitations• Follow station policy• Plan your sortie in cool hours of the day• Adequate fluid intake• Do not exert prior to sortie• Adequate interval and rest between sorties

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CONCLUSION

• Heat stress cannot be eliminated completely and is still a problem in military flying

• Simple precautionary measures can considerably reduce heat strain to acceptable levels

• Proper thermal control helps a long way in success of missions & enhances flight safety

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QUESTIONS??

THANK YOU