The paper presents the result of the experimental study on explosive spalling of artificial lightweight aggregate concrete in fire.
According to the results, main factors which influence upon explosive spalling of concrete are (1) cement content, (2) moisture content of test specimen, and (3) time-temperature curve of furnace. Other factors, such as unit water, age, and size of test specimen have influence, too.
Under usual conditions, artificial lightweight aggregate concrete containing less than 350kg/m³ of cement is safe from explosive spalling.
Artificial lightweight aggregate concrete can be protected from explosive spalling by adding fire proof covering to the surface of test specimen, or using river sand and/or gravel with artificial lightweight aggregate,

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According to the Report of the Tokyo Fire Department, some fires, though rather rare, were caused by the spontaneous ignition of wooden materials contacting, for a long time, with steam pipes for heating rooms. It is doubtful, however, that wooden materials can really catch fire at this low temperature (100-150°C), even in the most favorable conditions, i.e. with a favorable rate of air supply and with the least dissipation of heat produced by oxidation.
These conditions are fulfilled by using a large sphere of saw-dust. Thus, the spontaneous ignition of a large saw-dust sphere suspended in a room of temperature T_a was studied.
It has been well known theoretically that whether the temperature of the sphere rises up beyond T_a and the sphere ignites spontaneously or the temperature cannot exceed T_a to the last depends on the value of a discriminant. This discriminant δ is defined as
δ= A/kr²(E/RT_a²)exp(-E/RT_a)
where A= the rate of heat production per unit volume of saw-dust when T_a is supposed to be infinitely large= 1.46× 10⁹cal. cm^-3. s^-1., E= the activation energy= 26.1 kcal. mol^-1, R= the gas constant= 2.0 cal. K^-1, k= the conductivity of saw-dust= 1.4×10^-4 cal. cm^-1. s^-1. °C^-1, and the condition for the spontaneous ignition is δ>3.32.
This theory has been experimentally verified by many authors, but they have dealt with small balls which caught fire when heated above 180°C.
Our experiment was carried out with a sphere 25cm of radius. The result showed that the critical temperature was 130°C which coincides remarkably with the theoretical value.
Thus, it is certain that wooden materials in the favorable conditions ignites spontaneously at a temperature as low as 130°C and are expected to do so at 100°C when piled in a large amount which corresponds to a saw-dust sphere 80cm of radius.
The time needed for ignition is very long and exceeds occasionally 240 hours, and the thermocouple inserted in the center showed that the temperature was kept at a constant value of 65°C for the most part of this long period.
The cause of this stationary state was studied theoretically with assumptions :
(1) water vapor diffuses through the space between the pieces of saw-dust,
(2) these pieces contain water and supply vapor to the space,
(3) in the innermost part, the vapor is saturated for the temperature at the point, and
(4) the diffusion coefficient of vapor through the saw-dust is smaller than that through the open air.
It was revealed that when the ratio of the former diffusion coefficient to the latter is about 0.5, the stationary temperature takes the value 65°C. The ratio 0.5 is considered reasonable from the distribution of pieces in the sphere.

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[in Japanese]

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[in Japanese]

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