If the low pressure is at the vent (e.g. Bernoulli + windy day) the higher ambient air pressure at the drain will push the water through the trap and up the ven

If the low pressure is at the vent (e.g. Bernoulli + windy day) the higher ambient air pressure at the drain will push the water through the trap and up the vent pipe. This would only be temporary, but if gases have accumulated near the trap they could diffuse back through the trap and into the room. These would seem to be exceedingly temporary situations however and not likely a source of chronic exposure to pipe gas. The only exception here might be if some HVAC imbalance keeps the ambient pressure in the room at 3-5" of head pressure over the vent.