Fire experiments were repeatedly conducted in a fire resistant 2-story house to investigate the toxicity of atmosphere in its 2nd floor room, using one of the 1st floor rooms as the burn room. Only the size of the opening to the 2nd floor room was varied in each fire experiment. Toxicity was found to become sufficiently high to cause death to rabbits exposed to gases taken from any location in the 2nd floor room, even when the doorway to the 2nd floor room was almost invisibly narrow. Major toxicants were limited to CO and HCN, as in our earlier work. Although the blood cyanide level was always below 2.0μg/ml, it is considered that HCN considerably contributed to incapacitation or death to the rabbits, because the COHb level mostly remained below 50% and, because the concentration of other toxic species was negligible.

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Within today's advanced information society, it has become more and more important to prevent fires in cable tunnels where power cables and telecommunications cables are housed. Despite the existing technologies for fire-retardant treatments for cable sheathing, prevention of a cable tunnel fire is still a major issue because fire-retardant cables are quite expensive, because considerable time and money are required to replace the conventional cables with fire-retardant ones, and bccause even fire-retardant cables can burn under certain conditions.
The authors have made a miniature simulation of a cable tunnel carefully designed so that it reflects the conditions of an actual cable tunnel to study fire behavior in cable tunnels. The study clarified the following:
(1) Polyethylene cables, which are highly combustible, generate a large quantity of dark smoke. When they burn in a tunnel, the temperature in the tunnel rises to more than 300 °C. It is possible to forecast the rise of temperature and smoke density inside the tunnel by using an approximate function.
(2) Fire-retardant vinyl cables are highly self-extinguishing even when they are forcibly ignited. As a result they hardly cause fire to spread. However, if these cables are loosely bundled so that air can flow among them, the cables could keep burning depending on the air flow speed.
(3) With a bundle of both polyethylene cables and fire-retardant vinyl cables, the polyethylene cables keep burning if the air flow speed is more than 0.4 m/s, and the heat generated by the burning polyethylene cables helps the fire-retardant vinyl cables burn, causing the fire to spread.
(4) Temperature sensors and smoke sensors are both effective in the detection of the early stages of a tunnel fire. However, temperature sensors, especially of the spread type, are more effective in locating the fire source.
(5) The detection of a cable tunnel fire may be effectively carried out with a gas sensor for CO and/or H₂ in addition to a temperature sensor and a smoke sensor.

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An experimental study has been performed to examine the effects of opening position on room fire characteristics, using a small-scale model room. The model room is a 50 cm-cube chamber with an opening of variable position and area. A circular fuel vessel of 10 cm in diam. and 2 cm in depth is installed at the center of the floor, and fuel used is ethanol.
It has been elucidated that the effects of the opening position on room fire characteristics are as significant as those of the ventilation parameter. Even if the opening configuration is fixed, i. e., the ventilation parameter is constant, the temperature distribution and gas flow field in the chamber change in wide ranges.
When the ventilation parameter A√H is small, extinction occurs, and as A√H increases, combustion becomes oscillatory and then stable. The limiting values at the transitions between these states depend largely on the distance h from the floor to the opening center. For larger values of A√H, the dependence of mass burning rate of ethanol on h is significant. For a certain case, the rate of the maximum to minimum at a constant values of A√H exceeds 1.8.

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