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Kestrel 4400 Heat Stress Meter

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Kestrel Meter 4400 Heat Stress Meter

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The Kestrel 4400 is revolutionary in size, cost and capability for those in need of measuring Heat Stress.
Along with having a Wet Bulb Global Temperature reading, the Kestrel 4400 displays thermal work limit (“TWL”), another recognized composite heat stress prediction tool. For both WBGT and TWL, the Kestrel 4400 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 4400 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 4400 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 4400 Work?

The Kestrel 4400 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.

Customized Warning Zones

Users from different work environments or different standards around the world have the ability to create their own warnings on the Kestrel 4400.  With the user friendly functionality, the user may  go into the Kestrel 4400's WBGT function and turn different warning zones on or off and set these warning zones to be triggered at different degrees as the temperature rises. By customizing the Kestrel 4400's WBGT warning zones, monitoring a team or crew becomes much more personal. A chart with suggested warning zones will be included with every Kestrel 4400 ordered. 


Kestrel Meter 4400 Heat Stress Meter Videos


The Kestrel Meter 4400 Heat Stress Meter measures/features

  • Wet Bulb Globe Temperature ("WBGT")
  • Thermal Work Limit ("TWL")
  • Globe Temperature
  • Naturally Aspirated Wet Bulb Temperature
  • Wind Speed
  • Max Wind Gust
  • Average Wind Speed
  • Temperature
  • Altitude
  • Pressure trend
  • Barometric pressure
  • Relative humidity in %
  • Heat stress index 
  • Dewpoint
  • Wet bulb temperature
  • Density altitude
  • Wind chill
  • Air, water, and snow temperature °F or °C
  • Current, average, and maximum air velocity
  • Waterproof and floats
  • Time and date
  • Easy- to-read backlit display
  • Data Logger (automatic and manual)
  • Customizable data storage - 2900 data points
  • Minimum, Maximum and Average values
  • Multi-Function 3-line display
  • Humidity sensor can be recalibrated in the field with our Relative Humidity Calibration Kit.
  • Exterior temperature, humidity, and pressure sensors for fast and accurate readings
  • Customize screens to display user-selected measurements
  • Graph and recall trends
  • User-replaceable impeller
  • Flip-top impeller cover allows use of other functions while protecting the impeller
  • Data charting
  • Upload to a computer (with optional interface)
  • Meets MIL-STD-810F 516.5 Procedure IV Transit Shock test - 20 drops from 5 ft. IP-67 sealed to exclude dust and water at 3 ft. submersion
  • Five languages (English, French, Spanish, German, and Italian)
  • US Patent Nos. 5,783,753 and 5,939,645 and 6,257,074
  • Assembled in the USA


    Here are just a few of the markets that need to reference WBGT for work or play:  

    • Athletes (high school, college, professional)
      • Athletic trainers 
    • Military training units & medics
    • Law enforcement medics 
    • Industrial hygienists
    • Construction supervisors 
    • Others working in extreme heat conditions


    Advantages of the Kestrel 4400 vs. Competition

    • Fraction of the size
    • Less than half of the cost
    • Equal or better accuracy
    • Fast response
    • Simple user interface 

    Kestrel Meter 4400 Includes

    • Batteries - 2 AAA*
    • Kestrel Portable Vane Mount 
    • Belt carry case
    • Neck lanyard
    • Kestrel Certificate of Conformity 
    • A chart with suggested Heat Stress warning zones.

    Kestrel Meter 4400 Additional Information 


    *We ship every Kestrel 4000 Series Meter exclusively with Made in the USA Energizer® Brand Ultimate Lithium AAA batteries for improved reliability, capacity, cold-weather performance and weight. We strongly recommend that you use only Energizer Ultimate Lithium batteries in your Kestrel Meter. If you choose to install alkaline batteries, we recommend that you do NOT store your Kestrel with these batteries installed, and that you check your batteries for leakage and corrosion a minimum of every 30 days. Damage due to leaking alkaline batteries is not covered under warranty.



      The History of Adopting Heat Acclimatization Guidelines

      In 2003 the NCAA began implementing heat acclimatization guidelines. Since the NCAA started these guidelines there has only been one death in collegiate football during the pre-season period, where prior to 2003 there had been an average of 1-2 every pre-season (saving an projected 15 lives). In 2009 the NATA released guidelines very similar to those of the NCAA.  Since these have been released, KSI has been working with many state athletic associations (as well as others) to assist these states in the adoption of the guidelines for high schools as well as other sport levels. The table below reflects the timeline of those that have adopted these guidelines:



      Date Guidelines Were Adopted


      New Jersey

      National Football League


      North Carolina







      May, 2003

      May, 2011

      July, 2011

      October, 2011

      February, 2012

      March, 2012

      June, 2012

      June, 2012

      June, 2012

      March, 2013

      April, 2013



                      No Guidelines
                      Deficient, but working with KSI to improve
                      Number of guidelines that match KSI recommendations
      0 1 2 3 4 5 6 ALL  


      State KSI approved guidelines Deficient, but working with KSI Has guidelines, but deficient No guidelines
      Alabama (AL)      
      Alaska (AK)      
      Arizona (AZ)      
      Arkansas (AR)      
      California (CA)      
      Colorado (CO)      
      Connecticut (CT)      
      Delaware (DE)      
      District of Columbia (DC)      
      Florida (FL)      
      Georgia (GA)      
      Hawaii (HI)      
      Idaho (ID)      
      Illinois (IL)      
      Indiana (IN)      
      Iowa (IA)      
      Kansas (KS)      
      Kentucky (KY)      
      Louisiana (LA)      
      Maine (ME)      
      Maryland (MD)      
      Massachusetts (MA)      
      Michigan (MI)      
      Minnesota (MN)      
      Mississippi (MS)      
      Missouri (MO)      
      Montana (MT)      
      Nebraska (NE)      
      Nevada (NV)      
      New Hampshire (NH)      
      New Jersey (NJ)      
      New Mexico (NM)      
      New York (NY)      
      North Carolina (NC)      
      North Dakota (ND)      
      Ohio (OH)      
      Oklahoma (OK)      
      Oregon (OR)      
      Pennsylvania (PA)      
      Rhode Island (RI)      
      South Carolina (SC)      
      South Dakota (SD)      
      Tennessee (TN)      
      Texas (TX)      
      Utah (UT)      
      Vermont (VT)      
      Virginia (VA)      
      Washington (WA)      
      West Virginia (WV)      
      Wisconsin (WI)      
      Wyoming (WY)