²³While pure SF₆ gas is benign, it should be noted that one of the potential chemical byproducts of arcing in an SF₆-quenched circuit breaker is hydrofluoric acid (HF) which is extremely toxic. HF is formed when SF₆ gas arcs in the presence of water vapor (H₂O), the latter being nearly impossible to completely eliminate from the interior chambers of the circuit breaker. This means any maintenance work on an SF₆-quenched circuit breaker must take this chemical hazard into consideration.