Before a worker enters a permit-required confined space, the employer must FIRST:

Explanation

Section 5157(d)(5) requires the internal atmosphere to be tested with a calibrated direct-reading instrument BEFORE entry - oxygen first, then combustible gases and vapours, then toxic air contaminants - and the results are recorded on the permit. Testing comes first because it determines everything after it. Ventilating first (a) is the usual control once the atmosphere is known, and blind ventilation can make things worse, drawing in engine exhaust or sweeping a flammable mixture through its explosive range. An attendant and a retrieval line (c) are required for the entry and tell nobody whether the space is safe to enter. And a supplied-air respirator (d) presumes the answer: if the testing shows an atmosphere immediately dangerous to life, the entry does not proceed unless the space is made safe or entered under the rescue provisions.