gastight

Gastight describes the ability of a container, enclosure, or joint to prevent the passage of gases under specified conditions. A gastight system relies on a combination of seals, gaskets, welds, and compatible materials to minimize permeation and leaks. The term is used across laboratory, industrial, and packaging contexts, and implies a level of containment suitable for maintaining inert atmospheres or preventing gas leaks.

Leak tightness is usually verified by leak testing, often using helium as a tracer and a mass spectrometer or by pressure decay methods. The performance is expressed as a leak rate, such as volume of gas per unit time per pressure difference (for example, mbar L/s or atm cm3/s). Acceptable limits depend on the application, with stricter requirements for inert atmosphere boxes and semiconductor processing equipment.

Common gastight applications include glove boxes and containment enclosures that maintain a controlled atmosphere; gas-tight packaging for sensitive products (MAP and vacuum-sealed items); glass ampoules and reactors designed to be sealed from the environment; and cryogenic dewars and vacuum-insulated vessels where gas entry must be minimized.

Materials selected for gastight designs balance low gas permeability with mechanical properties and chemical compatibility. Permeation through materials (like plastics) can occur over time or with temperature changes, so seals are chosen for compatibility and longevity. Repeated sealing cycles can degrade gaskets, increasing leak risk.

In practice, gastightness is assessed against the specific performance requirements of the intended use, and maintained through regular inspection, testing, and replacement of worn components.