The air valves provide double protection: prevent from evaporating potentially hazardous liquids and, as well, withhold dust and pollutants entering with air to the vessel. There is also available a fireproof version of all Safety Caps range.
When a Safety Cap is said to be suitable for PFAS (Poly- and Perflouroalkyl Substances) analysis, it means that the cap is designed for use in tests that aim to detect the presence of fluorine in a substance.