Loss of Lemmings: Zero
Jump one out, and Glue, thus covering the gaps. Rope from the second glue bridge to the concavity in the pipework, just left of and below the green and white block. Let it walk up the rope and reflect, making it Bomb while standing on the rope hook, just as it has turned to go left - this will ensure it continues to go left when it lands stunned, which isn't important for this bomb but is for subsequent ones. Let it come back and walk up the remnant of the rope, then Rope from the top of it to the top left corner of the block. Scoop right while actually standing on the block, then immediately convert the scooper to a Roper, and rope up to the concave elbow of the next pipe. Bomb the pipe, again ensuring the Lemming is facing left. When it comes back, Rope horizontally to the grenn stuff, so the rope is placed not far above the steel, and so the top of the hook is a few pixels removed from the rope. Bomb once more. When it returns, Rope a final time to complete the path to the exit. Use a Glue Pourer to create a step, releasing the horde.