Inflammable gas concentration monitoring is an important part of centralized monitoring system in coalmine. That assists safety mining operation without gas explosion or gas combustion in deeper gassy coal faces in Japanese coal mines. Experiencing serious inflammable gas related disasters, a lot of efforts had been paid on researches and developments of inflammable gas measurement systems. Considerable financial resources distributed to the installation of inflammable gas measurement system in underground coalmines. However, as Japanese mine safety management system has not employed probabilistic evaluation, the total effect of the measurement system and reliability had not been evaluated before.
Therefore, the question about excess of shortage of safety measure had caused. To derive the answer to the question, the authors investigated inflammable gas measurement system of a Japanese coalmine, and analyzed its reliability, especially in instantaneous failure rates.
The authors developed Fault Tree about gas explosion or combustion accidents in relation with detection failure of inflammable gases. Then, we identified failures of the measurement system using Failure Modes and Effective Analysis format.The authors collected failure frequency rates data by site measurements, interviews about error frequency, and questionnaires about humane errors.
As the result of those surveys and analysis, the authors obtained the following data; yearly drift error value and error rates of automatic inflammable gas alarms (detectors), error rates of the whole automatic methane detection system, human error rates of portable interferometer type methane detectors. Based on the data, the authors calculated the total instantaneous failure rates of whole automatic methane detection system. Then compare the present system with '60th and '80th system and discussed about potential surplus rule and over safety measurement devices installation in mines.
