1. In driving tunnels and other undergound projects by the single section technique or with an upper lead section, peripheral blasting may prevent overage if the work is done without bracing or with an anchor bracing. 2. Peripheral blasting should be used, depending on the strength of rocks: with a closer spacing of charges in stable rocks; with a preliminary cut-off in the unstable rocks. 3. In working the lower bench following the driving of the lead section—always prior to concreting—it is necessary to blast the preliminary cut-off by placing the charges in boreholes as in the open-cut. 4. In driving the proximate parallel cuts, only the preliminary cut-off will protect the barrier from the effects of peripheral blasting.