Complex sentence: First, when the envelope was already inflated, it was found that the bottom of the envelope dangerously mingled with the ropes; a volunteer, someone Fyodor Tereschenko, climbed the rope and untied the knots.
Split into simpler sentences: First, when the envelope was already inflated, it was found that the bottom of the envelope dangerously mingled with the ropes. A volunteer, someone named Fyodor Tereschenko, climbed the ropes and untied the knots.