Defining the effects of ambient conditions in large-scale fire tests

The paper documents the results of an analysis of the effects of ambient conditions, temperature and relative humidity, on the development of large-scale fires during their initial growth. While the study has focused on the behavior of hygroscopic cartoned commodities, because their burning behavior is greatly affected by propensity to absorb ambient moisture, non-hygroscopic materials and their reduced sensitivity to ambient humidity could also be considered. The analysis introduces the heat release rate at the time of first sprinkler activation as a meaningful measure to represent the impact of ambient conditions on the development of a free-burning fire. The next step of estimating the behavior under extinguishment conditions is not possible at this time, though general considerations on expected trends are offered on the basis of the results obtained from another research program. The practical output of the work is in the form of the identification of the desirable range of operating conditions for ambient temperature and relative humidity in large-scale fire testing.