Complex sentence: Engineer boots are designed to protect the wearer from injury to the foot and leg: for motorcycle riders, in the case of an accident while riding and to prevent burns of the rider's legs and feet from the heat of the motorcycle parts while riding.
Split into simpler sentences: Engineer boots are designed to protect the wearer from injury to the foot and leg. For motorcycle riders, in the case of an accident while riding and to prevent burns of the rider's legs and feet from the heat of the motorcycle parts while riding.