erupt / irrupt
To burst out versus to burst in.
To erupt is to burst out: a volcano erupts; laughter erupts. To irrupt is to burst in. Irrupt is rare. If you mean a sudden outburst, write erupt.
Examples
UseThe crowd erupted.
UseDeer irrupted into the yard.
AvoidThe crowd irrupted. (If you mean they burst out, not in.)