Before anyone enters a 12 ft deep sewer manhole classified as a permit-required confined space, the atmosphere is tested and the meter reads 19.2 percent oxygen. What is the correct interpretation, and in what order must the atmosphere be tested?

Giải thích

An acceptable atmosphere holds oxygen between 19.5 and 23.5 percent, so 19.2 percent is oxygen deficient and entry is prohibited until the space is ventilated and retested. Testing follows a fixed order of oxygen, then flammables, then toxics, because combustible gas sensors need oxygen to give a valid reading and a low oxygen result makes the flammability reading unreliable. An enriched atmosphere is above 23.5 percent, not below 19.5. A filtering facepiece only removes contaminants from the air; it cannot add oxygen, so it is never permitted in an oxygen-deficient space, which requires supplied air along with an attendant, a signed entry permit and a retrieval system.