A Sealer Oil must be added to the surface of all National Foam foam concentrates, except the Vaporshield and High Expansion types, immediately after the concentrate is placed in a storage tank. Sealer Oil serves as a sealing barrier between the foam concentrate and air and reduces the effects of evaportation and concentrate deterioration. A depth of approximately ¼” (6.35 mm) is required to provide an adequate seal. This procedure is not recommended for apparatus concentrate tanks or tanks subjected to excessive vibration.
Sealer Oil is a technical or U.S.P. grade white mineral oil having a viscosity between 200 to 500 SSU (44-110 centistokes) at 100°F (38°C).
Use, Discharge, and Disposal of Firefighting Foam Products