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Heat Related Illness





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Heat Related Illness and Bicycling


Heat related illness can manifest itself in as a number of symptoms.  In its various manifestations its impact can range from reduced productivity to death.  With proper precautions certainly the most serious consequences and most minor symptoms are avoidable.  Because of the potential for the quick onset of serious consequences for bicyclists it is good to review the issue at the beginning of every hot season with the objective of avoiding to the extent possible all heat related illnesses.


A review of relevant terms provides a good guide to what is important:

"Heat Related Illness” (HRI) is a serious medical condition resulting from the body’s inability to cope with a particular heat load, and includes heat cramps, heat exhaustion, heat syncope and heat stroke.

"Heat Stress Index” (HSI) refers to a formula or chart correlating higher temperatures and higher humidity with levels of heat stress and the likelihood of HRI.

"Environmental risk factors for heat illness” means conditions, working or recreation, that create the possibility that heat illness could occur, including air temperature, relative humidity, radiant heat from the sun and other sources, conductive heat sources such as the ground, air movement, workload severity and duration, protective clothing and personal protective equipment worn by subject.

"Personal risk factors for heat illness” means factors such as an individual’s age, degree of acclimatization, health, water consumption, alcohol consumption, caffeine consumption, and use of prescription medications that affect the body’s water retention or other physiological responses to heat.

"Shade” means blockage of direct sunlight. Canopies, umbrellas and other temporary structures or devices may be used to provide shade. Some shade producing areas are not adequate to cool the body; for instance, a car sitting in the sun does not provide acceptable shade to a person inside it, unless the car is running with air conditioning.

Unique Implication for Bicyclists

Heat and bicycling can be a trickier to handle than in a less dynamic situation.  For example: If the temperature is 86 o F (30 o C), with a relative humidity of 55%, and a breeze of  6 mph (10 kph), sitting under an umbrella in a park can be quite delightful.  If you are bicycling at 12 mph (20 kph), into the wind, the effective wind on your face is 18 mph (30 kph).  Even with radiant heat from the sun, this should make you feel quite comfortable.  But if the road turns and heads the opposite direction, the effective wind on your face will drop to 6 mph (10 kph), and with the relative high humidity, radiant heat and the exertion from bicycling, you can stew.  If you then come to an up hill where you slow down to 6 mph (10 kph) (reducing the ventilation to zero) and increase your exertion, your HSI can go through the roof and a crisis can develop quickly.  If you were already slightly dehydrated, all in the same atmospheric conditions that seemed comfortable a few minute earlier can become life threatening.

Implementation of Heat Stress Control for Bicycle Programs

As a maximum, we suggest a HSI of 90 (see chart) or any temperature over 89 o F (22o C) for when aggressive controls and methods should be put in place to ensure heat related incidents do not occur to employees and program participants.

Controls for reducing heat exposure:

  1. Drink plenty of water early in the day and continue drinking appropriate liquids through activity period.
  2. Start activities earlier in the day to avoid the heat of the day.
  3. Take extra rest breaks in a shaded or cool area (as needed) to avoid the heat related symptoms.

Provisions for water:

When the potential for HRI is high participants should carry enough water, or have a plan for re-supply, so that they can drink at least one liter per hour, if needed.  In high heat index conditions it is recommended that everyone drinks one cup (250 ml) of water every 15 minutes.

First Aid awareness and actions in the event of a heat related illness:

  • Heat cramps are painful muscle spasms that usually occur in the legs or abdomen. They are caused by the failure to replace fluids or electrolytes, such as sodium or potassium. Heat cramps are the least severe of heat related illnesses. Treatment includes moving a person to a cooler place, stretching muscles for cramps, and giving cool water or electrolyte-containing fluid to drink.
  • Heat exhaustion is an early indicator that the body’s cooling system is becoming overwhelmed. Symptoms include excessive thirst, sleepiness or tiredness, dry mouth, decreased urine output, headaches, dizziness, lightheadedness, or fainting; weakness and clammy or moist skin; mood changes such as irritability or confusion; upset stomach or vomiting. It can lead to heat stroke if ignored. Treatment includes moving the person to a cooler place, and if the person is conscious, providing small amounts of cool water to drink. Fan the victim to circulate the air while applying water with a cool cloth.
  • Heat stroke is a medical emergency caused by the failure of the body’s cooling system. Symptoms include dry, hot skin with no sweating; mental confusion or losing consciousness; seizures or fits. Treatment includes all of the elements for heat exhaustion and contact emergency medical assistance.


People working or recreating in high heat conditions should receiving training in the following:

  • Environmental and personal risk factors for heat illness
  • Procedures for identifying, evaluating, and controlling exposures to the environmental and personal risk factors for heat illness
  • The importance of frequent consumption of water
  • The importance of acclimatization
  • The different types of heat illness and the common signs and symptoms of heat illness
  • The importance of immediately reporting to a supervisor or designee symptoms or signs of heat illness
  • Procedures for responding to symptoms of possible heat illness, including how emergency medical services will be provided should they become necessary
  • Procedures for contacting emergency medical services, and if necessary, for transporting employees to a point where they can be reached by medical service personnel
  • How to provide clear and precise directions to the location of the emergency.

Supervisor training: Prior to assignment to supervision of employees or program participant working in the heat, training on the following topics should occur:

  • The information provided for employee/participant training (above).
  • Procedures the supervisor will follow to implement controls.
  • Procedures the supervisor will follow when an employee or participant exhibits symptoms consistent with possible heat illness, including emergency response procedures.

Return to Education: Bicycle Safety and Health Index.


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