Dead-air space is a term used to describe an unventilated area where no air circulates. The term can be used in different contexts, including:

• Construction: Dead-air space can refer to the spaces between panes of glass in insulated glazing. It can also refer to an area in a structure that has no ventilation and where air does not circulate.

• Physiology: Dead space can represent the volume of ventilated air that does not participate in gas exchange in the lungs. There are two types of dead space: anatomical dead space and physiological dead space. Anatomical dead space is the volume of air that fills the conducting zone of respiration, while physiological dead space is equal to anatomical plus alveolar dead space.

• Smoke alarms: Dead air space can also be a problem for smoke alarms. It is an unventilated space where air doesn’t circulate, often occurring where corners meet, like in the apex of a cathedral ceiling, in between exposed floor joists in the ceiling, or where the ceiling meets the wall. When a room fills with smoke, the smoke won’t penetrate dead air spaces because the trapped air and lack of circulation keeps the smoke out of that pocket. If a smoke alarm happens to be mounted in a dead air space, it won’t detect smoke properly because a pocket of air is keeping the smoke away from the alarm’s sensors.

In summary, dead-air space refers to an unventilated area where no air circulates, and the term can be used in different contexts, including construction, physiology, and smoke alarms.