Bulletin of Japan Association for Fire Science and Engineering

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In order to detect a compartment fire in the early stage and provide highly reliable fire information, it is necessary first to sense the fire phenomena as they change moment by moment and then make a judgment about the fire based on the data obtained.
The time-domain data of a fire cannot be attained by conventional sensors which are actuated at a fixed threshold level. To obtain such data, analog output type sensors should be used. However, because the behavior of a fire is not usually steady in the course of its progression, the main stream of the fire phenomena may not be precisely extracted if the analog sensor output data are used as they are for fire judgment. In the design of an intelligent fire alarm system, therefore, consideration should be given to the frequency response of the system.
Using the results of the analysis of the output data of temperature sensors and smoke sensors obtained from fire experiments, we have investigated the frequency response required for the intelligent system.
Our results show that in the early stage of a fire, the main frequency components of the fire phenomena in the course of its progression fall into the frequency band of from DC to 55 mHz for the temperature and from DC to 15 mHz for the smoke density. This implies that the temperature sensor output and the smoke sensor output should be filtered individually through these frequency bands. We also investigated the requirements for digital filters that glve the above frequency responses, and have clarified the relationship between the frequency response of the sensor itself, the cut-off frequency of the digital filter, and the data sampling interval.
The study shows that precise fire judgment can be made by an intelligent system where the sensor output data are preprocessed, as described above, before being sent to the fire judgment algorithm.

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A generalized theory on the critical water application rate in the wood crib fire extinction and wild fire suppression is discussed in this paper.
(1) Crib fire extinction
The energy pours into the burnable area in the wet area occupied 87-65% when the burnable critical radiative intensity of the char was assumed between 4,564 and 15,000 Kcal/m²·h. Besides because the flying sparkles and flames lick up the wet surface, it was considered the primary condition for the total extinction is to sweep the whole surface before a portion of the surface dries up. With the above basis and assumptions, a general equation expressed in terms of crib geometry was derived on the radiation model. The agreement with experiments seemed reasonable when the water was applied bottom up.
(2) Wild fire suppression
The fire will stop and disappear when the water dropped on the fuel surface in front of the fire front remains and resists against the radiative heat until the fuel is consumed. With this assumption the necessary density of water to be sprayed was calculated in case of ground fire and forest fire. Also for ground fire operations, the necessary area to spray water and its application rate was derived. These results seems to agree with empirical data.

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