This paper deals with the amounts of HCN and NH₃ formed by combustion and/or pyrolysis and the consideration of mechanism of HCN formation.
The combustion and pyrolysis were carried out in a quartz tube held in an electric furnace and gaseous products formed were collected in a series of 5 impingers containing KOH solution for HCN absorption, H₂SO₄ solution for NH₃ absorption respectively (Fig. 1). HCN was analyzed by the Liebig-Dénigès' silver nitrate titration method and NH₃ by the Folin's Nessler method.
The amounts of HCN formed by the pyrolysis or burning in air of polyacrylonitrile and nylon-6, increased, in most cases, with increasing temperature. In most of the cases, they decreased with the increase of relative air supply rate (the ratio of the air supply rate to the sample amount carried into the furnace in one time spoon operation), though on the contrary they increased in the range of very small relative air supply rate (Fig. 2 and 3). As for urea resin, melamine resin and polyurethane, HCN yields were so little affected by the relative air supply rate ranging from 0.5x 10^-2 to 2.5x 10^-2 1/min/mg that they were only related with the heating temperature (Fig. 4-6). Urea and melamine resins had their peaks in HCN yield at 650°C. HCN yeild from polyurethane increased with increasing temperature. According to Fig. 7, in the atmosphere of N₂, HCN formation occurred only at over 500°C with one exception, and increased with increasing temperature. Only polyacrylonitrile evolved HCN even at considerably low temperature of 300°C. HCN yield was proportional to the content of nitrogen in the case of pyrolysis temperature of 900°C, as shown in Fig. 8.
The findings mentioned above suggest that HCN formation is only dependent on thermal decomposition temperature. Thermal decomposition reaction is generally more brisk, as the temperature is higher. So, the amount of HCN formed is considered to increase with increasing temperature, whether the atmosphere is N₂ or air. But, when oxygen or air exists, it oxidizes HCN once formed and thus reduces the final HCN yield, though it contributes to the flame temperature rise which results in the larger HCN yield in some cases. In the case of urea and melamine resins burned at 800°C in air, most of HCN once formed was considered to be consumed by oxidation through flaming burning. Polyurethane will show the similar pattern to those of nylon-6 and polyacrylonitrile respectively in Fig. 2 and 3, if the relative air supply rate is varied more largely.
HCN was found in the gaseous products from all the nitrogen-containing low molecular organic compounds of different kinds used in the present experiments, when they were pyrolyzed at over 600°C in the current of N₂. Unlike many other compounds, lactonitrile and dimethylglyoxime evolved HCN even at the relatively low temperature of 300°-400°C, as polyacrylonitrile did. Dimethylglyoxime is the compound which could easily be turned into a nitrile by hydration. As polyacrylonitrile is believed to release HCN through dehydrogen cyanide reaction, so the other two are. The reason why such nitriles as acetonitrile, phthalonitrile and acrylonitrile did not release any amount of HCN at lower temperature than 600°C is probably that their thermal decomposition temperatures are rather high. The larger the content of nitrogen, the larger was the HCN yield in pyrolysis at 1000°C (Fig. 10). It shows the trend that the ratio of HCN yield to nitrogen content will converge some point at higher temperature than 1000°C regardless of chemical bonding or structure of compounds.
It was found that HCN was formed when a mixture of hexane and NH₃ or that of ethanol and NH₃ was heated in the current of N₂ (Fig. 9).

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In the preceding experiments, the signs have been obsereved through a glass window and the influence of stimulating effect (Lachrymal and Irritant effect) of smoke on visibility has been omitted.
In the present paper, to investigate such influence, observers walk to the back-lighted “EXIT” sign in the smoky corridor (20 meters long) and record the visibility at the obscuration threshold, at the distinguishable threshold of color, and at the legible threshold of letters of the sign (see Fig. 2). Fluoresent lamp of 10 W for normal operation and 3 pieces of tungsten filament lamps (2.5 V, 0.3 A) for black out are employed as the light source of sign (see Fig. 1). The stimulating smoke was generated from smoldering wood (neary white smoke), and unstimulating smoke was generated from kerosene (black smoke).
The visibility at the distinguishable threshold of color and at the legible threshold of letters of the sign in high stimulating smoke density (0.5/m of extinction coefficient) reduces by more than 30% compared with those in the same unstimulating smoke density (see Fig. 4 and Fig. 5). In stimulating smoke, especially high in density, it is more difficult to observe a sign because of lachrymation and irritation. Therefore, the apparent brightness contrasts of the distinguishable threshold of color and of the legible threshold of letters of the sign require large value compared with that in the same unstimulating smoke density (see Fig. 6 and Fig. 7). That is the reason why visibility in stimulating smoke is small.
Both the visibilities at the obscuration threshold of sign in stimulating and unstimulating smokes are about the same, because the apparent brightness contrast of obscuration threshold is little affected by stimulating smoke (see Fig. 3, Fig. 6 and Fig. 7).

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A piece of filter paper was rolled several turns to form a circular rod of 3.8 mm radius. When this rod was kept vertically and was kindled at its top, a flame proceeded downward.
Heat is transferred to an unburnt part by both the conduction through paper rod and the radiation from the flame. When the heat quantity given to the part comes up to a certain value, combustion reaction begins in this part resulting in the flame propagation to this layer. The study reported in this paper is concerned with the ratio of heat quantities transferred in both ways.
In order to observe heat radiation from the flame, we used a small square (2 mm × 2 mm) aluminum foil (thickness = 0.075 mm), on a surface of which the junction of a thermocouple of copper-constantan (dia = 0.12 mm) was stuck to form a radiometer of small size. Both surfaces of the foil were blacked out to make the radiometer more sensitive to the incident radiation. Its sensitivity was calibrated by a conventional thermopile-type standard radiometer.
The intensity of radiation on the radiometer, placed as close to the rod-surface as possible, was observed when the flame front attained to a point adjacent to the radiometer. From these reults, the incident radiation per unit time on the side of the disk, supposed in the rod just under the flame front, was calculated. On the other hand, heat gains by conduction per unit time of this disk was calculated from the temperature distribution in the rod and the conductivity of the filter paper.
Comparing both values, it has been found that the ratio of radiation intensity to the conductive heat gains is as small as 6.2/180. In setting up a theory of flame propagation along a vertical rod, therefore, one can ignore the effect of heat radiation, as a first approximation, compared with the heat conducted through the rod.

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Properties of water sprays injected into compressed atmospheres were studied in order to design an effective fixed spray system for use in a hyperbaric chamber. With the ambient pressure and the vertical distance from the nozzle, a contraction of the spray and an increase of droplet size becomes noticeable because the spray is decelerated more rapidly, commences to drop by the gravity at the higher position, and is transferred more easily toward nozzle axis by the entrained air and consequently the coalescence among spray droplets becomes remarkable. The entrained air velocity becomes a maximum at the spray axis mainly due to the inertia of induced air and so the diffusion of entrained air in the spray is smaller than that of air jet. As ambient pressure increases, the entrained air velocity generally decreases, but is approximately constant in the case of the swirl nozzle. The following spray characteristics are recommended for the extinguishment of fires in hyperbaric chambers :
(1) coarse spray ;
(2) low velocity or the homogeneous distribution of the entrained gas ;
(3) little contraction in the downward stream ;
(4) large flow rate.

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