Thermal Environment: Effects, Regulation, and Comfort

Item 14. Physical Agents: Thermal Environment

Introduction

Thermal environment refers to environmental conditions including:

• Temperature
• Humidity
• Physical activity

Homeotherms

Homeotherms maintain internal temperature within very narrow ranges.

• Danger: Heat stress
• Heat discomfort
• Comfort
• Discomfort from cold
• Danger: Hypothermia

Thermal Equilibrium

Thermal equilibrium between body and environment involves mechanisms of thermoregulation.

Mechanisms of Thermoregulation

Q = M ± R ± C - E

• Q: Heat generated or heat buildup
• M: Metabolic activity
• R: Radiation exchange
• C: Exchange by convection
• E: Heat lost by evaporation

Radiation Exchange (R)

Heat exchange that originates between two solid bodies in proximity.

Exchange by Convection (C)

Mechanism by which the body exchanges heat with surrounding air, influenced by:

• Air temperature
• Air velocity

Lost by Evaporation (E)

Heat removal mechanism through evaporation of sweat, influenced by:

• Humidity
• Air velocity

Effects on the Body

1. Systemic Alterations (Heat Stress)

1. Dehydration
   • <5%: Thirst (SED)
   • >10%: Concern and somnolence
   • >15%: Death
2. Heat Exhaustion
   • Fainting
   • Weakened pulse and fall in blood pressure
3. Heat Stroke
   • Agitation
   • Delirium
   • Shock
   • Death within 24 hours

2. Skin Disorders

1. Heat rash
2. Frostbite
3. Severe hypothermia (death)

3. Psychic Disorders (Thermal Discomfort)

1. Fatigue
2. Acute distress

WBGT Index (Wet Bulb Globe Temperature)

Recognized by the ACGIH to detect alert situations and picked up at the UNE-EN Nosmo 27,243.

1. Temperature balloon (TG): Radiant temperature
2. Temperature natural wet (THN): Temperature humidity
3. Temperature dry air (TA): Air temperature

Indoor without solar load: WBGT = 0.7 THN + 0.3 TG

Outdoor solar load: WBGT = 0.7 THN + 0.2 TG + 0.1 TS

Comfort Levels Recommended in the Workplace

• Temperature: 19-23 ºC
• Humidity: 40-70%
• Ventilation: Fresh air supply
  • Minimum: 8 liters/sec/person
  • Smoking: 16 liters/sec/person
  • Heavy Smoking: 25 liters/sec/person
  • Total supply air: 46 m³/h
• Air speed: 0.1-0.3 m/sec
• Noise: Maximum 46 dBa
• Lighting
  • Normal office work: 500 lux
  • Drawing, Correction: 50 lux

Sick Building Syndrome

Joint discomfort and ill health caused by poor ventilation, the imbalance of temperature, ionic electromagnetic loads, suspended particles, gases and vapors of chemical origin and bioaerosols, among other identified causative agents.

Symptoms of Sick Building Syndrome

• Fatigue and/or decay
• Itching and irritation of skin, eyes, nose, and throat
• Tearing, runny nose, and other allergic symptoms
• Shortness of breath, chest tightness
• Headache
• Nausea, dizziness, and vomiting
• Etc.