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

MI ROOM - ICGAS DAMAN

ENVIRONMENTAL FACTORS AFFECTING AIRCREW HEALTH

VIBRATION

NOISE

CIRCADIAN DYSRHYTHMIA

RADIATION

THERMAL STRESS

HYPOXIA

DECOMPRESSION

ACCELERATION

3MI ROOM - ICGAS DAMAN

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

4MI ROOM - ICGAS DAMAN

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

HEAT STRESS

5MI ROOM - ICGAS DAMAN

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

6MI ROOM - ICGAS DAMAN

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

7MI ROOM - ICGAS DAMAN

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

8MI ROOM - ICGAS DAMAN

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

9MI ROOM - ICGAS DAMAN

FACTORS AFFECTING HEAT TOLERANCE

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

10MI ROOM - ICGAS DAMAN

ALLEVIATION OF THERMAL STRESS

11MI ROOM - ICGAS DAMAN

ALLEVIATION OF THERMAL STRESS

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

12MI ROOM - ICGAS DAMAN

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

13MI ROOM - ICGAS DAMAN

• 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

14MI ROOM - ICGAS DAMAN

• 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

15MI ROOM - ICGAS DAMAN

INFLIGHT SOLUTION

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

16MI ROOM - ICGAS DAMAN

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

17MI ROOM - ICGAS DAMAN

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

18MI ROOM - ICGAS DAMAN

• 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

19MI ROOM - ICGAS DAMAN

• Liquid Conditioned Suits– Water through piped lining in

contact with skin– More effective– Difficult to maintain

PERSONAL CLOTHING

20MI ROOM - ICGAS DAMAN

• Gel Cooled Vests– New concept involving Flexum

material– Pre-refrigerated before use

PERSONAL CLOTHING

21MI ROOM - ICGAS DAMAN

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

22MI ROOM - ICGAS DAMAN

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

23MI ROOM - ICGAS DAMAN

QUESTIONS??

THANK YOU