This part of ISO 17491 specifies a method to be performed either at minimum test settings (Method 1) or at more rigorous test settings (Method 2), for assessing the resistance of a gas-tight suit to outward leakage of air through, for example, essential openings, fastenings, seams, interface areas between items, pores and any imperfections in the construction materials. This test does not simulate penetration by gases in an inward direction. Although the danger to the wearer arises from leakage in an inward direction, this test method assesses the outward leakage of air after the gas-tight suit has been inflated so as to stretch the construction material, thereby enabling the test method to detect very small imperfections, such as holes, splits or tears.