The presently available requirements with regard to the tightness of pipe connections for flammable, highly inflammable and potentially explosive media and fluids are clearly requesting tightness.
Explosive and highly flammable liquid fuels are already defined with regard to their temperature riseup to its ignition point and above, in some cases also up to 10°C or less below the flash point (wording according to SOLAS). In some cases certain technical regulations the 'technical tightness' is requested.
However, a clear definition of this qualitative requirement and about acceptable leakage rates are not existing at all. Instead of a clear definition, one tries, by means of additional requirements for technical protective means and organizational measures, to safeguard the tightness before commissioning and in operation and to minimize the risk in case of potential leakages.