Canadian Forest Service Publications

Relative humidity measurement for fire danger rating in Canada. 1989. Flannigan, M.D.; Litwin, P.J. Forestry Canada, Petawawa National Forestry Institute, Chalk River, Ontario. Information Report PI-X-93. 12 p.

Year: 1989

Available from: National Capital Region

Catalog ID: 11737

Language: English

Series: Information Report (Petawawa)

CFS Availability: Order paper copy (free), PDF (download)


Wet and dry bulb temperatures from ventilated and non-ventilated screens can be used to obtain realistic values of relative humidity provided the appropriate psychrometric coefficient is used. However, relative humidity from non-ventilated screens are subject to significant error when the weather is sunny or calm.

Our investigations revealed that thermohygrometers are poor for field measurement of RH whereas the PCRC-11 sensor and Vaisala humicap performed well.

There is a need for a sensitivity study of the Fire Weather Index with respect to relative humidity. We would also suggest the relative humidity lookup table be replaced by the Goff-Gratch equation. Finally, alternatives like using dewpoint temperature to obtain relative humidity or automating the system should be investigated.

Also available under the title:
Mesure de l'humidité relative pour l'évaluation des risques d'incendie au Canada (French)

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