The Kestrel 5400 is revolutionary in size, cost and capability for those in need of measuring Heat Stress. Available with or without LiNK (Bluetooth) and / or a compass.

Along with having a Wet Bulb Global Temperature reading, the Kestrel 5400 displays thermal work limit (“TWL”), another recognized composite heat stress prediction tool. For both WBGT and TWL, the Kestrel 5400 provides on-screen alarms when conditions enter the caution and danger zones, providing clear and immediate guidance that heat illness prevention steps must be taken. Clothing levels can also be customized, making the Kestrel 4400 particularly useful in activities requiring heavy protective gear which worsens heat stress. The Kestrel 5400 also displays natural wet bulb temperature, and black globe temperature.

Athlete deaths from heat exposure are on the rise. Warming summers have been accompanied by weekly reports of athletes young and old collapsing from severe heat-induced illness. Our military training units struggle to keep soldiers healthy while preparing them for the grueling heat of Iraq and Afghanistan. OSHA is campaigning to prevent heat illness in outdoor workers and reports that every year thousands of workers become sick working in the heat, and some even die. In every instance, accurate and localized measurement of heat stress conditions is a key component of a heat illness prevention plan. The Kestrel 5400 Heat Stress Tracker, new from NK, answers this need.

Human heat stress results from a combination of many environmental factors – air temperature and humidity along with radiant heat from the sun and surfaces, balanced by the cooling effect of breezes or air flow. Anyone who has stood under welcome shade adjacent to a sizzling parking lot understands that these conditions must be evaluated exactly where peoples’ activities are taking place. The most common composite measurement used to determine appropriate exposure to heat stress conditions is Wet Bulb Globe Temperature or “WBGT.” The American College of Sports Medicine, the American Conference of Governmental Industrial Hygienists, and the US Military all have published threshold limit values (TLV’s) or reference guidelines for conditions, activity levels and hydration based on WBGT, clothing levels and acclimatization of participants.

How Does the Kestrel 5400 Work?

The Kestrel 5400 uses a 1-inch black globe to gather information about the environment, which isn't possible with current Kestrels. As is true with the original Wet Bulb Globe Temperature apparatus, a temperature sensor is installed inside the globe that will measure the temperature inside. The temperature inside the globe is a function of the ambient air temperature, solar insolation and wind speed.

As one can imagine, a sunny day will make the globe hotter because it's painted black, and colder ambient temperatures will have a tendency to cool off the globe. Lastly, the wind will cause the globe to get closer to the ambient air temperature because it will carry heat away from the globe when the air is cooler, or increase heat transfer to the globe if the air is warmer than the globe.

The Kestrel must sit out for a period of time to allow the globe to adjust to true atmospheric conditions; we recommend a minimum of 7-10 minutes. The globe temperature is then taken into account along with other measurements, such as ambient temperature, humidity and pressure, to calculate more meaningful measurements, such as Wet Bulb Globe Temperature and Thermal Work Limit.

The Kestrel Meter 5400 Heat Stress Meter Measures

Works with Compatible Apps:
(Screenshots of Kestrel Connect App with customizable screens)