An online time-based collaborative contribution system for the purchase of good or service includes a database, a server, a plurality of user devices, and a user interface provided at each user device. , and which thermally decomposes the waste gas to which the decomposition assist gas has been added; an acidic gas treating device for removing acidic gases from the thermally decomposed waste gas; and channels or lines for connecting these devices in sequence. The risk control matrix storage unit stores a risk control matrix in which a correspondence relation between the risks and the controls is described.