Recently, lethal disaster has often occurred in case of fire breakout. The toxicity of gases generated with fire has been highlighted. Such disasters are attributable to an increase in the number of sufferers to a fire due to an extensive scale of building constructions or a large quantity of transportation. In the future, the scale of buildings has a tendency to become larger, thereby increasing the number of sufferers proportionately with said tendency.

Fire casualties are classified in two types of a direct casualty due to fire, i.e. combustion fire and an indirect casualty due to smoke and gas which spread and fill up a building and inhibit an escaping behavior with resulting in deceases. In many cases men who stay on a floor on which a fire breaks out are often saved, but men on floors upper than said floor fail to escape and are caused to death. Namely, a man who starts a fire is saved for himself, although men unrelated with him suffer to serious damages.

The security of human lives in a fire of buildings must depend on the escaping behavior and the smoke and gas which are generated in case of fire breakout and the speed of their diffusion in a building. When appraising the security of building against a fire, of course, the fire-extinguishing action must be also taken into consideration from the view points of the security of lives and the protection of properties. It is ideal that buildings safe to fires are ones in which a fire never break out, or men need not escape entirely even if a fire breaks out.

However, this idea can not be realized from the view point that men live and work in a building because not only some combustibles in the building in accordance with the use of spaces therein but also various heat are directly or indirectly brought thereinto.

Accordingly, plans for smoke prevention are required so that a smoke load and gas load are decreased of to their threshold limit concentrations necessary for the scale and the fenants of a building when they diffuse in the building. These smoke load and gas load varies with the kind (chemical composition) of substances which are burning in a fire section and the opening condition (flow state of air). Therefore, a rational safety countermeasure can be achieved by providing means for decreasing the concentrations of smoke and gas and a means for preventing and shielding smoke which suits with this purpose.

Today, a term "smoke prevention" is often used. After all, the combustion products may be classified roughly as follows:

Anyone of them is a inhibiting factor to the human escape. In general, the smoke, described here, will be treated as a factor inhibiting the distance of vision, which is evaluated by an optical characteristic value (coefficient of light diminution). Studies in this field proceed well with establishing the logical system and clarifying the relation between the concentration of it and the effective distance of vision (threshold limit concentration).

On the contrary, as for gases, the history of studies is short, leaving many problems unsolved and not establishing an evaluating method concerning the toxicity of gases. As a result, the threshold limit concentration of gases is not found and it is difficult to establish plans for smoke prevention.