A brake toggle entangling the prop can be fatal. Two fatalities have been caused by it, one captured on video. It’s most likely to happen right after launch, when thrust is pushing the motor towards the riser, and you let go of the brakes. It’s far more likely with low attachment machines because their geometry puts the top cage close to your risers and brake toggles. If you fly such a machine, it is best that the space between your first and second (or inner and outer) hoop have netting to reduce the possibility.
Normally, air friction against the long brake line (between pulley and trailing edge) pulls the brake toggles against their stops. But in some cases, letting go of a toggle without carefully putting it at the pulley, can allow it to flail and be sucked into the prop. Usually it just breaks the toggle off and you face the lesser emergency of having no brake on that side. However, if it wraps into the prop, you’re doomed into an irrecoverable spiral.
One possible fix is John Fetz idea with a lightweight bungee cord that prevents the toggle from going too far while allowing full brake travel.
This should only be done by experienced pilots or instructors who can anticipate possible side effects. Be extremely careful not to introduce more risk than you mitigate. For example, attaching a 2nd brake line to lower hand position, adds more material that can foul the prop.
Put a ring around your brake toggle, it may require untying the brake. A thick round ring would be best so the line doesn’t abrade. Run a 1/8″ bungee from the hook-in loop for the slip ring. If you incorporate a 2nd brake toggle (like in the diagram at right), rin The slip ring allows the primary brake to easily overpower the light bungee while still pulling the brake away from the prop..