Abstract
The authors have identified the cause of an accident which occurred during the excavation work of a tunnel in a National Highway costruction in an area of Wakayama Prefecture to be a high concentration of CO2 and a marked O2 deficit in the air of the accident site. Furthermore, the mechanism of the O2 deficit and the generation of the high concentration of CO2 has been deduced to be such that the geological characteristics of the particular stratum called Itogawa-Butsuzo Line passing the site of the tunnel excavation were acting as a main factor, and that the physical and chemical actions of the shale absorb O2 and discharge CO2. Itogawa-Butsuzo Line is a well-known geological structural line like the Central Structural Line passing southwestern Japan and Mikabu Line. The danger of incidence of such an accident as stated above is, therefore, conceivable in this area and other areas having such a structural line. And, sufficient precautions must be taken for a construction work in such a stratum of the earth, or such a structural zone should be avoided as much as possible by a scrupulous geological survey before the construction. It is absolutely necessary to conduct complete ventilation in the tunnel during the excavation if the excavation in sush a stratum is unavoidable. As hygienic management measures, the personnel in charge of health supervision in such a construction site ought to be supplied with the necessary instruments, reagents, and birds ready for detecting various gases at regular intervals in order to guard against the disaster. The authors deeply acknowledge various assistances ext5ended by Wakayama Labor Standard Bureau from the outset of our investigation, the help of the Industrial Science Laboratory of Kao Soap Co., Ltd. which took up the precision gas analysers, and the kind advice given to our geological investigation by Mr. Tsutomu Iwahashi, Assistant Professor of the Geological Laboratory, School of Education of Wakayama University.
