Wednesday, May 22, 2013

How hot, how cold?

Why it may not be strictly “risk management,” protecting personnel from the elements is – should be – important to all practitioners.

In the summer

The thermometer may not record a really warm temperature, but the body complains it’s too hot for comfort.

The problem is a combination of temperature and relative humidity.

    What IS “relative humidity?”

    Relative humidity, as defined by The Free Dictionary is “The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage.” (See .)

The formula for figuring out the heat index is more than a little complicated, but no one has to be a math maven to get the numbers.

The National Weather Service (NWS) has an online function that lets people plug in the important numbers

    Temperature in F or C (but not K)

    Relative Humidity in percentage.


If you really MUST know the formula, the NWS has the formula linked from the calculator page; click on “How do we calculate the heat index?

There even is a heat index chart link – “Heat Index Chart and Explanation” – just below the calculator at … heatindex.shtml.

In the winter

The NWS comes to the rescue once again, this time at

Links from this URL connect to a Wind Chill Calculator and to both New Wind Chill Chart and Old Wind Chill charts.

Like the heat index calculator, the wind chill calculator requires two inputs:

    Temperature in F or C

    Wind speed in mph

(You can convert metrics to miles per hour at Online Conversions at

New Wind Chill Chart

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