Sausages are a ground meat therefore need to be cooked thoroughly. On a BBQ the heat of the flames will quickly bring the juices of the sausage past boiling point, causing the sausage to split, losing their flavoursome juices. A better way to BBQ sausages is to give them 1 to 2 minutes over high heat to colour and char the meat. Then turn down the heat or move to a cooler part of the grill and allow them to cook slowly until done.