Heat Stress Monitors, Help Athletes, Workers Keep Their Cool in Hot Environments

Summers can be brutally hot, and when high temperatures mix with high humidity, it slows the evaporation of sweat, inhibiting the body's ability to release heat quickly. Heat-related illnesses occur when the body's temperature control system becomes overloaded, potentially damaging vital organs. Heat-related illnesses can range from heat cramps to heat exhaustion to the most serious, heat stroke.

Heat stroke can cause body temperatures to rise to 41°C or higher within 10 to 15 minutes and can cause death or permanent disability if emergency treatment isn't received. So whether activities include sports, kids playing at school or daycare, or employees who work in heat intensive situations - indoors or outdoors - how hot is too hot and when should work or activity be stopped?

Exposure limits intended to minimize the risk of heat-related illnesses are set by provincial and territorial governments for most Canadian workplaces, and by Human Resources and Skills Development Canada (HRSDC) for workplaces under the federal jurisdiction. Though there is currently no specific maximum temperature at which activity should be stopped, some Canadian jurisdictions and the Ministry of Labour, have adopted the Threshold Limit Values (TLVs) recommended by The American Conference of Governmental Industrial Hygienists (ACGIH) as occupational exposure limits or guidelines to control heat stress in the workplace.

The TLVs are given in units of wet bulb globe temperature (WBGT) degrees Celsius (°C). The WBGT unit takes into account environmental factors like air temperature, humidity and air movement, and in some cases, heat from radiant sources, which all contribute to a person's perception of hotness. WBGT differs from the heat index, which takes into consideration temperature and humidity, and is calculated for shady areas. The WBGT Index is the most widely accepted measure of environmental conditions and is used as a monitoring guideline for activities in both athletics associations and industry. The wet bulb globe temperature (WBGT) is calculated by using the following equations:

For outdoors with direct sun exposure: WBGT = 0.7 x Tempwet bulb + 0.2 x Tempglobe + 0.1 x Tempair
For indoors or outdoors without direct sun exposure: WBGT = 0.7 x Tempwet bulb + 0.3 x Tempglobe

The U.S. Government Occupational and Environmental Health Bulletin list several of the WBGT index general guidelines, which include the following: WBGT Index = 78.0 - 81.9¡F. Extremely intense physical exertion may precipitate heat exhaustion or heat stroke; therefore caution should be taken. WBGT Index = 82.0 - 84.9¡F. Discretion should be used in planning heavy exercise for unseasoned personnel. This is sometimes used as the marginal limit of environmental heat stress. WBGT Index = 85.0 - 87.9¡F. Strenuous exercise such as marching at standard cadence should be suspended in unseasoned personnel during their first three weeks of training. Training activities may be continued on a reduced scale after the second week of training. Outdoor classes in the sun should be avoided above this temperature. WBGT Index = 85.0¡F or greater. Outdoor classes in the sun should be avoided. WBGT Index = 88.0¡F. Strenuous exercise should be curtailed for all recruits and other trainees with less than 12 weeks training in hot weather. WBGT Index = 90.0¡F or greater. Physical training and strenuous exercise should be suspended for all personnel (excluding essential operational commitments not for training purposes, where risk of heat casualties may be warranted).

To prevent heat collapse, workers should gradually become acclimatized to the hot environment. The ACGIH publication "2008 TLVs and BEIs" also provides recommended screening criteria for heat stress exposure for workers acclimatized to heat and for workers who are not acclimatized to heat. Acclimatization is the temporary adaptation of the body to work in the heat that occurs gradually when a person is exposed to it. Acclimatization peaks in most people within four to fourteen days of regular work for at least two hours per day in the heat.

Are an effective instrument in determining how long a person can safely work or play or remain in a particular area. These portable, lightweight meters measure environmental conditions such as temperature, relative humidity, heat stress index, wet bulb temperature, wet bulb globe temperature (WBGT) and several other environmental parameters. Many heat stress meters on the market like REED and KESTREL offer high tech benefits, including user-settable warning zones that let you know when your threshold is exceeded, and they're easy-to-use with quick setup and on-the-spot readings.

Nothing beats a common sense approach to heat illnesses. Remember, anyone exposed to hot and humid conditions is at risk of heat illness, especially those doing heavy work or using bulky protective clothing and equipment. Some individuals might be at greater risk than others if they have not built up a tolerance to hot conditions.

Personal Risk Factors In addition to environmental factors, personal risk factors can increase a person's susceptibility for heat illness, all of which can affect the body's water retention or other physiological response to heat:

  • a person's age
  • degree of acclimatization
  • overall health
  • water, alcohol, and caffeine consumption
  • poor circulation
  • use of prescription medications

Warning Signs of Heat Stroke

  • Extremely high body temperature (over 38°C)
  • Red, hot and dry skin with no sweating
  • Rapid, strong pulse
  • Throbbing headache
  • Dizziness
  • Nausea
  • Confusion
  • Unconsciousness

Warning Signs of Heat Exhaustion

Heat exhaustion is milder form of heat illness than heat stroke, but should be taken just as seriously.

  • Heavy sweating
  • Fast, shallow breath
  • Cool, moist skin
  • Fast, but weak pulse
  • Paleness
  • Muscle cramps
  • Tiredness
  • Weakness
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Fainting

How to Cool the Body and Protect Against Heat Illness

  • Drink cool, non-caffeinated, non-alcoholic beverages
  • Stop and rest
  • Take a cold shower
  • Put a cold or wet towel around your neck
  • Get out the sun into a shady or air conditioned environment
  • Wear light-weight clothing
  • If possible, postpone outdoor activity until the coolest part of the day

Employers, workers, athletes and coaches should watch for signs of heat-related illness, not only in themselves but also in each other, and pay particular attention to the elderly and children, who are most susceptible to heat-related illnesses. Use heat stress meters to measure WBGT and other environmental factors, and be prepared to seek and provide medical assistance.

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