Short answer
Permeation is a behavior related to the ability of a fluid to pass through the hose material; it is not the same as a visible hole or a fitting leak. In gas transfer, the inner tube, gas type, pressure, temperature and ambient ventilation must be evaluated together.
Technical explanation
Manufacturer safety guides explain that some fluids can pass through the hose material and that accumulation in the surrounding environment can pose a risk. The chemical resistance of PTFE does not mean that permeation is negligible for every gas. If there is permeation data in the catalog, it is read together with the test conditions. Passing a liquid pressure test does not mean that gas permeation or gas tightness has been verified under all conditions of use.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Fluid | Gas type and mixture |
| Conditions | Pressure, temperature and duration |
| Environment | Ventilation and accumulation risk |
| Evidence | Product-specific permeation assessment |
How is it assessed in practice?
In a gas line assessment, record the identity of the fluid, operating and standstill conditions, enclosed volumes and possible accumulation points. If an odor or a detector alarm occurs around the line, do not attribute it solely to fitting tightness; ask for a competent inspection after safe isolation. Do not write 'PTFE is impermeable' in the specification without manufacturer data. When comparing alternative materials, use data under the same gas, pressure and temperature conditions.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Does a chemically resistant hose not let any gas through at all?
This conclusion cannot be drawn. Chemical resistance and permeation are separate properties.
Source coverage
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S017
Parker Safety Guide, Publication 4400-B.1 Parker Hannifin · accessed 2026-10-20 PDF page 2; 2.6 PermeationPDF page 2; 2.5 Fluid Compatibility | PDF page 2; 2.6 PermeationPDF page 2; 2.2 Pressure | PDF page 2; 2.6 Permeation
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S024
Hose and Flexible Tubing, MS-01-180 Swagelok · accessed 2026-10-19 PDF pages 4–5 / printed 253–254: Nomenclature; pages 8–9: selection, installation and use