How Heat Stress Harms Workers

Chemical reactions in every cell are optimal at 37°C
Even ±2°C deviation can be life-threatening

Muscles are only ~10% efficient
Over 90% of energy from physical work becomes heat

The body must continuously dissipate this heat to the environment

Above 37°C ambient, evaporation of sweat is the ONLY cooling mechanism

High humidity blocks sweat evaporation — heat cannot escape

Result: core temperature rises → heat illness → death if unchecked

Normal Function

Delivers oxygen & nutrients to muscles & organs

Carries heat from working muscles to skin for dissipation

Volume: ~5L (men) / 4L (women)

Sweat comes from blood volume initially

When Dehydrated

↓ Blood volume → less blood to skin → heat not dissipated

↑ Heart rate to compensate → excessive fatigue

↓ Blood to gut → slower fluid absorption

↓ Blood to muscles → reduced work capacity

↓ Blood to brain → poor concentration, accidents

Performance Decrements (Bates et al., 2013):

• 1–2% dehydration: 6–7% reduction in physical work rate
• 3–4% dehydration: 22–50% reduction in work rate (moderate to hot environments)
• Mental performance: Begins declining at just 2% dehydration — accident risk rises significantly

What Is Sweat?

A 10-Hour Shift in Gulf Heat

What to Drink

✓ Water + electrolyte solution
3–4g carbohydrate, 10–20 mmol/L sodium per 100ml is ideal

✓ Programme drinking
Small amounts frequently — do NOT wait until thirsty

✗ Avoid high-sugar sports drinks
Most contain >7% sugar — slows gut absorption

✗ Avoid caffeinated drinks on-site
Coffee, Coke, energy drinks are diuretics (increase urination)

✗ Never use alcohol to rehydrate
3L beer when 3L dehydrated → still 3.5L deficit!

Caffeine Content in Common Drinks

Alcohol-induced dehydration effect

Heat Collapse (Fainting)

Who is at risk:
Workers unaccustomed to heat who stand upright and immobile for extended periods

Mechanism:
Blood pools in legs → inadequate venous return → insufficient blood to the brain → fainting

Signs:
Dizziness, pale/clammy skin, sudden collapse without prior warning of heat exhaustion

First Aid:
Lie flat with legs elevated; move to cool area; monitor closely; call medical if unresponsive

Prevention:
Keep workers moving (even light activity); acclimatisation programme; no standing still in heat

How Heat Causes Accidents

Sweaty palms:
Reduced grip → dropped tools, equipment slips, handling errors

Dizziness & lightheadedness:
Fall from height, loss of balance on scaffolding or plant equipment

Fogging of safety glasses:
Obscured vision → contact with moving machinery or hot surfaces

Hot surfaces / steam:
Contact burns — impaired judgement delays avoidance reaction

Reduced alertness:
Slower reaction time, poor decision-making, missed hazard warnings

Irritability & anger:
Interpersonal conflict → distraction, reduced focus, physical incidents

What Acclimatisation Achieves

Acclimatisation Timeline (Physiological)

Age: Older workers have reduced cardiovascular reserve; less efficient sweating mechanism

Body Weight (BMI): BMI >30: 2× injury risk. Less surface area relative to body mass — less cooling capacity. More heat generated

Physical Fitness: Fit workers have greater aerobic capacity — withstand more heat stress; acclimatise faster

Prior Illness: Flu, diarrhoea, vomiting, hangover = pre-dehydrated. Short-term illness dramatically raises heat illness risk

Medication: Some medications impair sweating or blood pressure control. Workers on medication need medical clearance for hot work

Acclimatisation Status: New starters need 10–21 days to acclimatise. Never let new workers work alone in first week

Alcohol Night Before: Alcohol is a diuretic — workers arrive dehydrated. Night-before drinking is a major heat illness risk factor