For heat and products of combustion to exhaust during positive-pressure ventilation, where must there be an opening?

The correct answer is based on the principles of fire dynamics and ventilation strategies. For effective positive-pressure ventilation (PPV) to work, there needs to be a proper opening for the heat and products of combustion to exhaust. Placing the opening near the seat of the fire allows for the most efficient removal of superheated gases, smoke, and other combustion byproducts that are concentrated in that area.

When the opening is near the seat of the fire, it facilitates the upward movement of hot smoke and gases, which rise due to their lower density relative to cooler air. By allowing these products to exit close to where they are generated, PPV can create a strong airflow that helps to push fresh, cooler air into the space. This not only helps control the fire but also improves visibility and reduces the risk of flashover and backdraft scenarios.

In contrast, an opening located above the fire could lead to the heat and smoke escaping without effectively assisting in the fire suppression efforts, as it could draw air in from lower levels without addressing the immediate source of the heat. An opening below the fire would not help in exhausting the hot gases that rise, and having an opening only on the fire floor would not create the necessary pressure differential to push the heat and smoke