Beating the Heat – Protecting Workers in Hot Environments

Heat stress is a very dangerous condition that affects many employeess, particularly those performing physical activities in hot and humid working conditions, indoors or outside, particularly during the summer months. Heat stress not only is dangerous to workers' health, but it also decreases workers' productivity and the quality of their work.

Heat stress can manifest itself in many ways, including heat rashes, heat cramps, heat exhaustion and ultimately, heat stroke. Although heat rashes and heat cramps can be both uncomfortable and affect workers' ability to do their jobs, heat exhaustion and heat stroke are much more serious and require immediate attention.

WARNING SIGNS

Numerous warning signs for heat-related illnesses exist. Recognizing these warning signs allows a worker to take the appropriate steps to get the situation under control. Some of the warning signs are headache, lightheadedness, dizziness, unusual fatigue, irritability, confusion, nausea/vomiting, cramping and diarrhea. These signs manifest due to the body redirecting blood from internal organs and muscles to the skin in an attempt to shed the heat. Plus, the sweating action means a loss of fluids and possible dehydration.

The illustration on pg. 54 shows the temperature and humidity levels where heat stress is likely to occur and where it becomes dangerous. At temperatures between 85 and 95 degrees F with humidity levels from 30 percent to 60 percent, heat stress is possible. When temperatures rise above 95 degrees F and humidity above 60 percent, workers are in even greater danger. Some heat-related illnesses include:

Heat rash — Skin irritation caused when sweat cannot freely evaporate from the skin and sweat glands become blocked. Wearing clothes that allow sweat to evaporate and taking breaks to allow skin to dry will help.

Heat cramps — Sweat results in loss of body fluid and salts. Depletion of salt in muscles can cause muscle spasms and cramping. Staying hydrated and replacing salts will help.

Heat exhaustion — The loss of large amounts of fluids (and sometimes salt) causes symptoms like fatigue, headache, dizziness and nausea. Staying well hydrated, replacing salts and taking regular rest breaks will help. Heat exhaustion can be the precursor to heat stroke.

Heat stroke — The body's temperature rises so rapidly and high that the normal cooling mechanisms cease to function and the body is unable to cool down. The victim's skin is hot and usually dry. Immediate medical treatment and first aid is needed. Move the victim to a cool area, remove or wet clothing and vigorously fan the person to increase the cooling effect while waiting for medical personnel to arrive.

HOW THE BODY COOLS ITSELF

The body continually generates heat that must be released in order to maintain the proper core temperature of 98.6 degrees F. The body responds to the increased temperature by circulating more blood to the skin, which allows the body to radiate more heat into the air. If heat loss from increased blood circulation is not adequate, the brain signals the sweat glands in the skin to release sweat onto the skin surface. As the sweat evaporates, it draws the energy to vaporize from the rest of the sweat on the skin, leaving cooler moisture on the skin, which helps reduce the overall core temperature. This is called evaporative cooling.

There are four basic mechanisms to cool the body:

Radiation — Almost 65 percent of all body heat is lost through radiation. This occurs when the heat from the skin is absorbed by the surrounding cooler air.

Convection — Approximately 10 percent of body cooling comes from heat transfer due to moving cool air (from a breeze or fan) across the skin to encourage evaporation and heat loss.

Conduction — Approximately 2 percent of body heat is pulled away by direct contact with a cooler object. The heat on the skin is transferred to the cooler object in contact with the skin.

Evaporation cooling — Moisture on the skin's surface (sweat) evaporates, taking heat away and leaving cooler moisture and skin.