15.
It is a sudden combustion process of great intensity accompanied by release of large quantities of heat energy and in which original gas or solid substance converted instantaniously in to gasious products . . . . . . . .

18.
The ventilation of drives exceeding 50 m length to be such as to dilute the nitrous fumes produced by blasting to . . . . . . . . and CO to . . . . . . . . within a period of . . . . . . . . min in long tunnel.