Getting to Know Heat Stress

It is that time of year.  The “Dog Days of Summer.”  In many areas of the Midwest it is expected to be hot and humid.  Workers young and old are being exposed to heat and humidity but may not yet be acclimated.  Let’s review some important principles of heat exposure and the signs and symptoms of heat exhaustion and heat stroke. 

Signs, Symptoms & First Aid
 
The first thing to know is how to recognize the signs and symptoms of heat cramps, heat exhaustion and heat stroke. ​

Heat Cramps:  Symptoms include:

• Muscle cramps and Pain
• Spasms in the Abdomen, arms or legs.

 
First Aid for Heat Cramps: 

• Stop all activity and sit in a cool or shaded place
• Drink clear juice or a sports beverage or water with food
• Avoid strenuous work for a few hours after cramps subside.
• Seek medical attention if the patient has heart problems, is on a low sodium diet, or if cramps don’t subside after one hour. 

Heat Exhaustion:  Symptoms include:

• Rapid heartbeat
• Heavy sweating
• Extreme weakness or fatigue
• Dizziness or headache
• Nausea or vomiting
• Fast, shallow breathing
• Slightly elevated body temperature

 
First Aid:

• Rest in a cool or shaded place
• Drink lots of water or other cool beverage
• Take a cool shower or place cool, wet rags on the person

​  
Heat Stroke:  This is a condition that occurs when the body is unable to control body temperature which can lead to permanent disability and death.  Symptoms include:

• High body temperature
• Confusion
• Loss of coordination
• Hot, dry skin or profuse sweating
• Throbbing headache
• Seizures or loss of consciousness

 
 
First Aid 
·         Request immediate medical assistance.
·         Move the worker to a cool, shaded area.

• Remove excess clothing and apply cool water to their body.

Heat Stress Regulations & Guidance
 
There are no specific regulations for heat stress, but MIOSHA, OSHA, ACGIH, NIOSH and NOAA all have guidance and information to educate employers on how to keep workers safe from heat induced illnesses.  A good place to start is the Heat Index published by NOAA.  ​

​Heat Index:  The heat index is the “feels like” temperature we hear from the local weather station and it incorporates both temperature and humidity.  The higher the heat index the hotter it will feel and the greater the risk of workers experiencing heat-related illness.  The index is broken into four levels of risk: Caution; Extreme Caution; Danger and Extreme Danger.  

​Humidity Matters  

Relative humidity is the amount of moisture in the air.  The higher the humidity the harder it is for the body to cool itself through evaporation of sweat resulting in the air temperature feeling hotter.  Contrary to that, very low humidity can also cause problems if our sweat evaporates too quickly causing dehydration if a person does not drink enough water. 
 
An important side-note about the NOAA heat index is that the values were developed for shady, light wind conditions.  This is a critical consideration because exposure to full sun can increase heat index values by up to 15 degrees F.  As a result, solar load needs to be considered when developing protective measures for a particular job or work site. 
 
ACGIH Threshold Limit Value
 
In the back of the ACGIH TLV and BEI booklet is a Thermal Stress section that includes heat stress and strain guidelines.  The section includes a decision tree, the use of Wet-Bulb Globe Temperature, clothing adjustments and other criteria to provide a TLV and action level for planning purposes to avoid heat strain.  The section also includes warnings about the TLV being based on the ability of most healthy people who are also acclimatized.  The TLV does not apply to people with prior heat stroke, heat exhaustion, cardiac or kidney problems, pregnancy, obesity or older workers, among others. 
 
Heat-Related Illness Prevention Plan

Whether you are looking at ACGIH, OSHA or other heat stress guidance, having a plan for a particular job or job site that will be proactive in protecting workers is a plus.  Depending on the environmental conditions, acclimation of workers and their overall health, some plan elements are as follows:

• Providing water, sports drinks rest areas and other supplies as needed for the job site. 
• Emergency preparedness in case a worker experiences heat exhaustion or heat stroke. 
• Allow workers to acclimatize over time through efficient use of increasing workloads and frequent breaks. 
• Provide for modified work schedules to avoid high heat and sun conditions for certain activities.
• Train workers in the signs and symptoms of heat stress and preventative measures before they get to the job site or before it gets hot.  
• Monitoring of the workers by visual and verbal methods to check for signs of heat stress. 
• Track the weather conditions for the work site, assess the risk and determine which prevention measures will be needed during the work schedule. 
• Implement your plan when the heat index is greater than 80 degrees F and adjust the risk levels based on direct sun exposure, shade, wind conditions, work load and type of protective clothing. 

 
The following links have some helpful information for developing and implementing a Heat-Related Illness Prevention Plan, including an OSHA-NIOSH Heat Safety app downloadable to a cell phone:  

NIOSH Heat Stress page

OSHA Heat Stress Quick Card

OSHA Working in the Heat page

NOAA Heat Index page