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Positive Pressure Test <br />This test is very like the negative pressure test, and it has the same <br />advantages and limitations. It is conducted by closing off the exhalation <br />valve and exhaling gently into the facepiece. The fit is considered <br />satisfactory if slight positive pressure can be built up inside the facepiece <br />without any evidence of outward leakage. For some respirators, this method <br />requires that the wearer remove the exhalation valve cover and then carefullv <br />replace it after the test, often a difficult task. Removing and replacing <br />the exhalation valve cover often disturbs the respirator fit even more than <br />does the negative pressure test. Therefore, this test should be used <br />sparingly if it requires removing and replacing a valve cover. The test is <br />easy for respirators whose valve cover has a single small port that can be <br />closed by the palm or a finger. The wearer should perform this test (Figure <br />B-2) just before entering any hazardous atmosphere. <br />= .,: <br />-: ,.~ :~ <br />, ,~ . <br />. . ~,~^r ~ <br />~'. <br />i ~ ~ ~~~ <br />.~~" s,: <br />FIGURE B-3. Positive pressure test <br />-149- <br />