Abstract: A system for supervising and guiding workers at various places in a construction such as an underground substation, underground market, building, or tunnel is disclosed which includes a number of receivers arranged in a number of sections of the construction for receiving infrared radiation emitted from workers to produce a detection signal, a detection device arranged in a central control room for processing the detection signals supplied from the receivers to detect positions of workers in the construction, and communication devices provided in each section and the central control room for providing the workers with various kinds of instructions, commands and messages for preventing a disaster and escaping an emergency.

Abstract: An alkali metal salt of carboxymethyl cellulose ether is prepared by dissolving an alkali in a water-containing organic solvent, adding starting cellulose to the solution, stirring the mixture to form a slurry of the alkali cellulose and then reacting it with an etherifying agent. Alternatively, it is prepared by reacting the starting cellulose in a water-containing solvent with sodium monochloroacetate as an etherifying agent, in the presence of an alkali.