In underground galleries being excavated where explosives are used, ventilation is carried out under the following conditions:
1° At least 200 litres of air per second per square metre of the largest section of the ventilated gallery are introduced at the working face by means of a mechanical ventilation system. The air introduced is taken far from any source of pollution;
2° After each blast, suction is applied as close as possible to the working face in order to eliminate suspended dust as far as possible;
3° If necessary, auxiliary ventilation is used to accelerate absorption of the blast plug.