Fingering is one of the flame spreads in a narrow space. In this study, it is found that flame front circularity distinguishes fingering flame spread from uniform flame spread. When the radius of flame spread was 40 mm and the circularity decreases as flame spreads, it was defined as fingering flame spread. When the circularity is larger than 90 %, it was defined as uniform flame spread. Using data obtained from these, it was indicated there are stable and unstable regions of flame spread from the relationship between the flow velocity and the radius of the flame spread with the diffusion equation.

In a large parking lot and garage, the fire spreads between the parked cars after the adjacent car is ignited first, and there is a possibility that the fire spreads to the building. It is important for safety design of large-scale parking lots and garages to clarify the possibility of spreading fire to adjacent cars. In car arson cases, fire spread possibility to neighborhood buildings is often requested to be proven in order to make the arson crime be formed. In this study, we focused on radiative heat flux as the index for judging fire spread possibility. Car fire experiments with two 5-door hatchback cars arranged side by side were conducted, and the heat fluxes and spread possibility to the adjacent car were investigated. Ignition was initiated at the left front tire with 80 g of kerosene and 10 g of gasoline. A fire received car was paralleled on the right side of a fire originated car at a separation distance of 80 cm and 1 m, and then the car fire experiments were conducted. Heat flux meters were set up in surroundings of the experimental car, and the radiative heat fluxes were measured. In an experiment with a separation distance of 80 cm, it was observed that the fire spread to the adjacent car from the originated car. In an experiment of 1 m, the left front tire of the adjacent car was burst and the car body was burnly damaged, but the fire could not spread. The ignition characteristics of the tire and bumper of the experimental car were measured using a cone calorie meter. The flame of the burned car was modeled as a flat plate, and, the radiative heat fluxes at the lateral direction were calculated. The possibility of fire spread was predicted from the calculated radiant heat flux at the lateral direction of the burned car and the ignition characteristics of the tire, and the predictions were in agreement with the combustion experiment. Furthermore, the possibilities of fire spread at the front and rear direction were predicted from the measured radiant heat flux and the ignition characteristics of the bumper.

In order to clarify the positive influence of the density on the ignition propensity for cotton products, heat transfer and temperature distribution inside a radiation-transmitting solid are examined under radiative spot-heating. The temperature distribution is numerically calculated for a bare cotton block of 60 mm × 60 mm × 30 mm, which is heated from its top by a spot-heating lamp at the heating power of 1.12 W. The absorption coefficient of the cotton is assumed to be proportional to the density, and its coefficient is obtained experimentally. Heating experiments are also conducted; the spot temperature of the experiment does not agree quantitatively well with that of the simulation, however, qualitative agreement is confirmed in its time variation and the dependency on the density. The simulation shows clearly that the maximum temperature resides inside the block and increases with density until the density reaches 160 kg/m³, but it then decreases in the denser region, where experiments have not been done. These results infer that the radiative heat transfer inside the solid is the key factor of the density dependence of the ignition propensity of the cotton products.