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Negative Pressure Test <br />The wearer can perform this test by himself in the field. The wearer should <br />use this test (Figure B-1) just before entering any toxic atmosphere. It <br />consists merely of closing off the inlet of the canister, cartridge(s), or <br />filter(s) by covering with the palm(s) or replacing the seal(s), or of <br />squeezing the breathing tube so that it does not pass air; inhaling gently so <br />that the facepiece collapses slightly; and holding the breath for 10 <br />seconds. If the facepiece remains slightly collapsed and no inward leakage <br />is detected, the respirator is probably tight enough. This test, of course, <br />can be used only on respirators with tight fitting facepieces. <br />`` 1 <br />,~~ <br />r <br />a <br />.~ <br />~ <br />FICURE B-2. Negative pressure test <br />-148- <br />