It was once thought that back fanged snakes were harmless to humans until someone was bitten by a Boomslang ( African Tree Snake) and unfortunately died. The only back fanged snakes which are deadly are the Boomslang and the African Vine Snake. These snakes have modifications that other back fanged snakes do not, such as grooved fangs and a venom sack as well as a potent venom. A lot of back fanged snakes which are completely harmless to man have now gained bad publicity( as venomous). A snake’s venom is designed to effect the prey that it eats, you will find that most back fanged snakes feed on frogs or lizards. Frogs and lizards do not pose a physical danger to the snake therefore the venom will be weaker as the prey does not need to be killed quickly and the back fanged snake simply chews the prey item, at the same time dripping venom into the preys body to subdue it. Therefore these snakes pose little or no danger to humans as it would take more venom than the snake can produce to harm you and it would have to be very toxic. You will notice that all the venomous snakes that eat mammals or birds have the strongest venom as these prey items have claws, beaks and teeth which could injure the snake. Rattlesnakes, Pit Vipers, Puff Adders, Gaboon Vipers, Cobras, Mambas, Taipans all feed on mammals and birds, do you see the point I am making.
Bellow are some Back Fanged Snakes which do have a medically significant effect on man.
Long Nosed Tree Snake
Olive Grass Snake
False Water Cobra