Improved Heat Safety App for Outdoor Workers

OSHA-NIOSH Heat Safety Tool

An updated app for smart phones and other mobile devices can help workers stay safe when working outdoors in hot weather. This free app was updated and redesigned by the National Institute for Occupational Safety and Health (NIOSH), along with the Occupational Safety and Health Administration (OSHA).

The OSHA-NIOSH Heat Safety Tool mobile app, for iOS and Android devices, determines heat index values—a measure for how hot it feels—based on temperature and humidity. Workers and their supervisors who may be exposed to hot and humid conditions, including construction workers, landscapers, farmers and others, are encouraged to use the app to check weather conditions if they will be working outdoors in the summer heat.

Extreme Heat Can be Deadly

Extreme heat causes more deaths than any other weather-related hazard; each year more than 65,000 people seek medical treatment for extreme heat exposure. In 2014 alone, 2,630 workers suffered from heat-related illness, and 18 died from heat stroke and related causes on the job, according to OSHA.

Work-related exposure to heat can also result in reduced productivity and growing risk of injuries, such as those caused by sweaty palms, fogged-up safety glasses and cognitive impairment (mental confusion, impaired judgment and poor coordination).

The app, an updated version of OSHA’s original Heat Safety Tool, uses the device’s geolocation capabilities to pull temperature and humidity data from National Oceanic and Atmospheric Administration satellites to determine the heat index. The app shows the current risk level (minimal, low, moderate, high or extreme) and forecasts the hourly heat index throughout the entire workday giving employers information they can use to adjust the work environment as needed to protect workers.

What is the Heat Index?

The heat index is a measure of how hot it feels when relative humidity is taken into account along with the actual air temperature. It is important to note that since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15°F.

The National Weather Service uses the heat index values to issue heat alerts. Because workers in hot environments experience heat stress from a combination of environmental factors and metabolic heat from the tasks they are performing, OSHA modified some of the heat index cutoffs to create heat index-associated protective measure for worksites.


The heat index and wet bulb globe temperature (WBGT) are both used to measure environmental temperature. NIOSH recommends the use of wet bulb globe temperature (WBGT) to determine the Recommended Exposure Limits (RELs) for acclimatized workers and the Recommended Alert Limits (RALs) for unacclimatized workers in hot environments. However, in many situations workers and small businesses will not have access to the resources necessary to determine WBGT. In these situations, using the heat index is a viable alternative.

WBGT is determined by measuring dry air temperature, humidity and radiant energy; it is used to calculate a thermal load on the worker. While the literature provides plenty of evidence regarding WBGT’s accuracy and common usage in industrial settings, the simplicity of the heat index makes it a good option for many outdoor work environments (as long as there are no additional radiant heat sources, such as fires or hot machinery).

The OSHA-NIOSH Heat Safety Tool App

The app provides recommendations to prevent heat-related illnesses and reduce heat stress in outdoor workers based on local weather conditions used to calculate the heat index. When you open the app, if your location services is enabled, the temperature and humidity data will automatically download and the current heat index will be displayed. Beneath the calculated heat index is the associated “precautions” button for the risk level. By clicking on “precautions,” you will arrive on a screen with risk level-specific recommendations.

If you are interested in planning your work activities for the entire shift around the heat index, an hourly feature allows you to scroll through and determine the hottest hours of the day along with the corresponding risk level and precautions. In addition, at the bottom of your app screen, you will always have easy access to heat-related illness symptoms and first aid. Also the “more tips” provides information about being prepared for emergencies, training, acclimatization, hydration, monitoring workers for heat-related illness and breaks. There is also a list of risk factors associated with heat-related illnesses.

Learn more about the OSHA-NIOSH Heat Safety Tool

Get the OSHA-NIOSH Heat Safety TOOL