Complex sentence: Within the space of only a few years there were horrific explosions at Cwmbach pit in 1846 when 28 miners were killed followed by the deaths, within three weeks of 4 others who had been seriously injured in the incident.
Split into simpler sentences: Within the space of only a few years there were horrific explosions. At Cwmbach pit in 1846 28 miners were killed, followed by the deaths within three weeks of four others who had been seriously injured in the incident.