This humidity business: what it is all about and its use in fire control
Document Type: Report
Author(s): Clive M. Countryman
Publication Year: 1971

Cataloging Information

  • dew point
  • fire control
  • fuel moisture
  • relative humidity
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Record Maintained By:
Record Last Modified: December 13, 2016
FRAMES Record Number: 8185


'Humidity' is an eight-letter word that is heard around fire camps and on the fireline almost as often as the more widely known four-letter words. Most firefighters know that humidity has something to do with moisture in the air. If it is low, they expect difficulty in controlling the fire; if it is high, the fire can be expected to burn less aggressively-and perhaps may even go out by itself. Humidity is a very general term, however. A weather specialist may use such confusing expressions as absolute humidity, specific humidity, mixing ratio, vapor pressure, dewpoint, and relative humidity. Each of these terms describes a different view of air moisture, and each has its value. But they all do not have the same importance in wildland fire control-relative humidity overshadows the rest. The following discussion is intended to sort out the meanings of different are moisture terms and show why relative humidity is so important.

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Countryman, Clive M. 1971. This humidity business: what it is all about and its use in fire control. Berkeley, CA: USDA Forest Service, Pacific Southwest Forest and Range Experiment Station. 18 p.