How long should the first rescue breath last?

The first rescue breath should last about one second. This duration is crucial because it allows for enough time to deliver an effective breath that can enter the person's lungs without causing excessive pressure. A breath that lasts too long could over-inflate the lungs or lead to injury, while a breath that is too quick may not provide sufficient air, making it ineffective. Thus, the one-second timeframe is a standard practice in CPR and emergency response for ensuring that the breath is delivered properly to aid in resuscitation.