Airtight

A hermetic seal is the quality of something—a container, structure, etc.—being airtight (excluding passage of air, oxygen, or other gases). Used technically, it is stated in conjunction with a specific test method and conditions of use.

The word hermetic comes from the Greek god Hermes, via the vocabulary of alchemy. The alchemists invented a process for making an airtight glass tube, which they used for distillation. The process used a secret seal, whose invention was attributed to the legendary inspiration of alchemy, Hermes Trismegistus.

Some kinds of packaging must maintain a seal against flow of gases: foods, pharmaceuticals, some chemicals and some consumer goods. The term can describe food preservation practices, such as vacuum packing and canning. Barrier packaging includes containers such as glass, aluminum cans, metal foils, and high barrier plastics.

Buildings designed with sustainable architecture principles use airtight technologies to conserve energy. Under low energy building, passive house, low-energy house, self-sufficient homes, zero energy building, and superinsulation standards, structures must be more air-tight than previously. Air barriers, careful sealing of construction joints and service penetrations (holes for pipes, etc.) achieve this. Airtightness minimizes the amount of warm (or cool) air that can pass through the structure, so the mechanical ventilation system can recover the heat before discharging air externally. Green buildings may include windows that combine triple-pane insulated glazing with argon or krypton gas to reduce thermal conductivity and increase efficiency. In landscape and exterior construction projects, airtight seals protect general service and landscape lighting electrical connections and splices. Many other specific applications must meet airtight standards to be waterproof or vapor-proof for human safety and proper function.

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