Hazard Knowledge

Heat illness covers a spectrum of conditions including heat exhaustion and heat stroke. In practice, it is difficult to distinguish between these conditions and they may coexist. For the purposes of this guidance the term heat illness refers to those individuals who become incapacitated as a result of a rise in core body temperature. 

Heat illness in personnel can be caused or exacerbated by: 

• Overexertion through physiological stress
• Exposure to high temperatures 
• Humidity 
• Inappropriate clothing or personal protective equipment (PPE) 
• Dehydration 
• Medical conditions or medication 

In addition to the hazards presented by heat illnesses, the conditions may adversely affect personnel in terms of decision making, or impairing the manual dexterity and physical ability of personnel. Because of this, personnel should self-monitor and be monitored for these conditions.

Heat stress 

Heat stress is a mild form of heat illness that can progress to more serious conditions such as heat exhaustion and heat stroke. Symptoms can include: 

• Fatigue 
• Heat syncope (fainting) 
• Swelling of feet and ankles 
• Heat cramps 

Heat exhaustion 

Heat exhaustion symptoms are mainly caused by the loss of fluids and body salts. Symptoms can include:  

• Headache, dizziness, nausea, vomiting and irregular pulse 
• Hypotension, sweating, muscle pain, weakness and cramps 

Heat stroke 

Heat stroke is the body’s response to an elevated core body temperature. If left untreated heat stroke can be life-threatening. The condition can have a sudden onset with no warning, or may be preceded by the symptoms of heat exhaustion. Symptoms can include: 

• Headaches, extreme fatigue, fainting, facial flushing 
• Vomiting and diarrhoea  
• Hot, dry skin with sweating being present in 50% of cases 
• Irregular pulse, hypotension, irregular breathing 
• Seizures  
• Rhabdomyolysis – the breakdown of muscle cells causing the release of toxins into the blood 

For further information on heat illness refer to: 

• Health and Safety Executive: Temperature in the workplace 
• Heat illness and cold injury: prevention and management (JSP 539)