Complex sentence: The biggest danger was that the safety lamps showed combustible gas within a short distance, these gasses were firedamp and afterdamp mixed with the black smoke emurging from the shafts, this meant that there was a serious treath for a second and even bigger explosion.
Split into simpler sentences: The biggest danger was that the safety lamps showed combustible gas within a short distance; these gasses were firedamp and afterdamp mixed with the black smoke emerging from the shafts. This meant that there was a serious threat for a second and even bigger explosion.